#ifndef RASTER_RENDERER_SYNTAX_H
#define RASTER_RENDERER_SYNTAX_H

#include "../core/basic.h"
#include "Lexer.h"
#include "Profile.h"

#include "../../Slang.h"

#include <assert.h>

namespace Slang
{
    class SyntaxVisitor;
    class FunctionSyntaxNode;

    class SyntaxNodeBase : public RefObject
    {
    public:
        CodePosition Position;
    };




    //
    // Other modifiers may have more elaborate data, and so
    // are represented as heap-allocated objects, in a linked
    // list.
    //
    class Modifier : public SyntaxNodeBase
    {
    public:
        // Next modifier in linked list of modifiers on same piece of syntax
        RefPtr<Modifier> next;

        // The token that was used to name this modifier.
        Token nameToken;
    };

#define SIMPLE_MODIFIER(NAME) \
    class NAME##Modifier : public Modifier {}

    SIMPLE_MODIFIER(Uniform);
    SIMPLE_MODIFIER(In);
    SIMPLE_MODIFIER(Out);
    SIMPLE_MODIFIER(Const);
    SIMPLE_MODIFIER(Instance);
    SIMPLE_MODIFIER(Builtin);
    SIMPLE_MODIFIER(Inline);
    SIMPLE_MODIFIER(Public);
    SIMPLE_MODIFIER(Require);
    SIMPLE_MODIFIER(Param);
    SIMPLE_MODIFIER(Extern);
    SIMPLE_MODIFIER(Input);
    SIMPLE_MODIFIER(Transparent);
    SIMPLE_MODIFIER(FromStdLib);
    SIMPLE_MODIFIER(Prefix);
    SIMPLE_MODIFIER(Postfix);

#undef SIMPLE_MODIFIER

    enum class IntrinsicOp
    {
        Unknown = 0,
#define INTRINSIC(NAME) NAME,
#include "intrinsic-defs.h"
    };

    IntrinsicOp findIntrinsicOp(char const* name);

    // Base class for modifiers that mark something as "intrinsic"
    // and thus lacking a direct implementation in the language.
    class IntrinsicModifierBase : public Modifier
    {
    };

    // A modifier that marks something as one of a small set of
    // truly intrinsic operations that the compiler knows about
    // directly.
    class IntrinsicOpModifier : public IntrinsicModifierBase
    {
    public:
        // token that names the intrinsic op
        Token opToken;

        // The opcode for the intrinsic operation
        IntrinsicOp op = IntrinsicOp::Unknown;
    };

    // A modifier that marks something as an intrinsic function,
    // for some subset of targets.
    class TargetIntrinsicModifier : public IntrinsicModifierBase
    {
    public:
        // Token that names the target that the operation
        // is an intrisic for.
        Token targetToken;

        // A custom definition for the operation
        Token definitionToken;
    };



    class InOutModifier : public OutModifier {};

    // This is a special sentinel modifier that gets added
    // to the list when we have multiple variable declarations
    // all sharing the same modifiers:
    //
    //     static uniform int a : FOO, *b : register(x0);
    //
    // In this case both `a` and `b` share the syntax
    // for part of their modifier list, but then have
    // their own modifiers as well:
    //
    //     a: SemanticModifier("FOO") --> SharedModifiers --> StaticModifier --> UniformModifier
    //                                 /
    //     b: RegisterModifier("x0")  /
    //
    class SharedModifiers : public Modifier {};

    // A GLSL `layout` modifier
    //
    // We use a distinct modifier for each key that
    // appears within the `layout(...)` construct,
    // and each key might have an optional value token.
    //
    // TODO: We probably want a notion of  "modifier groups"
    // so that we can recover good source location info
    // for modifiers that were part of the same vs.
    // different constructs.
    class GLSLLayoutModifier : public Modifier
    {
    public:
        // THe token used to introduce the modifier is stored
        // as the `nameToken` field.

        // TODO: may want to accept a full expression here
        Token valToken;
    };

    // We divide GLSL `layout` modifiers into those we have parsed
    // (in the sense of having some notion of their semantics), and
    // those we have not.
    class GLSLParsedLayoutModifier      : public GLSLLayoutModifier {};
    class GLSLUnparsedLayoutModifier    : public GLSLLayoutModifier {};

    // Specific cases for known GLSL `layout` modifiers that we need to work with
    class GLSLConstantIDLayoutModifier  : public GLSLParsedLayoutModifier {};
    class GLSLBindingLayoutModifier     : public GLSLParsedLayoutModifier {};
    class GLSLSetLayoutModifier         : public GLSLParsedLayoutModifier {};
    class GLSLLocationLayoutModifier    : public GLSLParsedLayoutModifier {};

    // A catch-all for single-keyword modifiers
    class SimpleModifier : public Modifier {};

    // Some GLSL-specific modifiers
    class GLSLBufferModifier    : public SimpleModifier {};
    class GLSLWriteOnlyModifier : public SimpleModifier {};
    class GLSLReadOnlyModifier  : public SimpleModifier {};
    class GLSLPatchModifier     : public SimpleModifier {};

    // Indicates that this is a variable declaration that corresponds to
    // a parameter block declaration in the source program.
    class ImplicitParameterBlockVariableModifier    : public Modifier {};

    // Indicates that this is a type that corresponds to the element
    // type of a parameter block declaration in the source program.
    class ImplicitParameterBlockElementTypeModifier : public Modifier {};

    // An HLSL semantic
    class HLSLSemantic : public Modifier
    {
    public:
        Token name;
    };


    // An HLSL semantic that affects layout
    class HLSLLayoutSemantic : public HLSLSemantic
    {
    public:
        Token registerName;
        Token componentMask;
    };

    // An HLSL `register` semantic
    class HLSLRegisterSemantic : public HLSLLayoutSemantic
    {
    };

    // TODO(tfoley): `packoffset`
    class HLSLPackOffsetSemantic : public HLSLLayoutSemantic
    {
    };

    // An HLSL semantic that just associated a declaration with a semantic name
    class HLSLSimpleSemantic : public HLSLSemantic
    {
    };

    // GLSL

    // Directives that came in via the preprocessor, but
    // that we need to keep around for later steps
    class GLSLPreprocessorDirective : public Modifier
    {
    };

    // A GLSL `#version` directive
    class GLSLVersionDirective : public GLSLPreprocessorDirective
    {
    public:
        // Token giving the version number to use
        Token versionNumberToken;

        // Optional token giving the sub-profile to be used
        Token glslProfileToken;
    };

    // A GLSL `#extension` directive
    class GLSLExtensionDirective : public GLSLPreprocessorDirective
    {
    public:
        // Token giving the version number to use
        Token extensionNameToken;

        // Optional token giving the sub-profile to be used
        Token dispositionToken;
    };

    class ParameterBlockReflectionName : public Modifier
    {
    public:
        Token nameToken;
    };

    // Helper class for iterating over a list of heap-allocated modifiers
    struct ModifierList
    {
        struct Iterator
        {
            Modifier* current;

            Modifier* operator*()
            {
                return current;
            }

            void operator++()
            {
                current = current->next.Ptr();
            }

            bool operator!=(Iterator other)
            {
                return current != other.current;
            };

            Iterator()
                : current(nullptr)
            {}

            Iterator(Modifier* modifier)
                : current(modifier)
            {}
        };

        ModifierList()
            : modifiers(nullptr)
        {}

        ModifierList(Modifier* modifiers)
            : modifiers(modifiers)
        {}

        Iterator begin() { return Iterator(modifiers); }
        Iterator end() { return Iterator(nullptr); }

        Modifier* modifiers;
    };

    // Helper class for iterating over heap-allocated modifiers
    // of a specific type.
    template<typename T>
    struct FilteredModifierList
    {
        struct Iterator
        {
            Modifier* current;

            T* operator*()
            {
                return (T*)current;
            }

            void operator++()
            {
                current = Adjust(current->next.Ptr());
            }

            bool operator!=(Iterator other)
            {
                return current != other.current;
            };

            Iterator()
                : current(nullptr)
            {}

            Iterator(Modifier* modifier)
                : current(modifier)
            {}
        };

        FilteredModifierList()
            : modifiers(nullptr)
        {}

        FilteredModifierList(Modifier* modifiers)
            : modifiers(Adjust(modifiers))
        {}

        Iterator begin() { return Iterator(modifiers); }
        Iterator end() { return Iterator(nullptr); }

        static Modifier* Adjust(Modifier* modifier)
        {
            Modifier* m = modifier;
            for (;;)
            {
                if (!m) return m;
                if (dynamic_cast<T*>(m)) return m;
                m = m->next.Ptr();
            }
        }

        Modifier* modifiers;
    };

    // A set of modifiers attached to a syntax node
    struct Modifiers
    {
        // The first modifier in the linked list of heap-allocated modifiers
        RefPtr<Modifier> first;

        template<typename T>
        FilteredModifierList<T> getModifiersOfType() { return FilteredModifierList<T>(first.Ptr()); }

        // Find the first modifier of a given type, or return `nullptr` if none is found.
        template<typename T>
        T* findModifier()
        {
            return *getModifiersOfType<T>().begin();
        }

        template<typename T>
        bool hasModifier() { return findModifier<T>() != nullptr; }

        FilteredModifierList<Modifier>::Iterator begin() { return FilteredModifierList<Modifier>::Iterator(first.Ptr()); }
        FilteredModifierList<Modifier>::Iterator end() { return FilteredModifierList<Modifier>::Iterator(nullptr); }
    };


    enum class BaseType
    {
        // Note(tfoley): These are ordered in terms of promotion rank, so be vareful when messing with this

        Void = 0,
        Bool,
        Int,
        UInt,
        UInt64,
        Float,
#if 0
        Texture2D = 48,
        TextureCube = 49,
        Texture2DArray = 50,
        Texture2DShadow = 51,
        TextureCubeShadow = 52,
        Texture2DArrayShadow = 53,
        Texture3D = 54,
        SamplerState = 4096, SamplerComparisonState = 4097,
        Error = 16384,
#endif
    };

    class Decl;
    class StructSyntaxNode;
    class BasicExpressionType;
    class ArrayExpressionType;
    class TypeDefDecl;
    class DeclRefType;
    class NamedExpressionType;
    class TypeType;
    class GenericDeclRefType; 
    class VectorExpressionType;
    class MatrixExpressionType;
    class ArithmeticExpressionType;
    class GenericDecl;
    class Substitutions;
    class TextureType;
    class SamplerStateType;

    // A compile-time constant value (usually a type)
    class Val : public RefObject
    {
    public:
        // construct a new value by applying a set of parameter
        // substitutions to this one
        RefPtr<Val> Substitute(Substitutions* subst);

        // Lower-level interface for substition. Like the basic
        // `Substitute` above, but also takes a by-reference
        // integer parameter that should be incremented when
        // returning a modified value (this can help the caller
        // decide whether they need to do anything).
        virtual RefPtr<Val> SubstituteImpl(Substitutions* subst, int* ioDiff);

        virtual bool EqualsVal(Val* val) = 0;
        virtual String ToString() = 0;
        virtual int GetHashCode() = 0;
        bool operator == (const Val & v)
        {
            return EqualsVal(const_cast<Val*>(&v));
        }
    };

    // A compile-time integer (may not have a specific concrete value)
    class IntVal : public Val
    {
    };

    // Try to extract a simple integer value from an `IntVal`.
    // This fill assert-fail if the object doesn't represent a literal value.
    int GetIntVal(RefPtr<IntVal> val);

    // Trivial case of a value that is just a constant integer
    class ConstantIntVal : public IntVal
    {
    public:
        int value;

        ConstantIntVal(int value)
            : value(value)
        {}

        virtual bool EqualsVal(Val* val) override;
        virtual String ToString() override;
        virtual int GetHashCode() override;
    };

    // TODO(tfoley): classes for more general compile-time integers,
    // including references to template parameters

    // A type, representing a classifier for some term in the AST.
    //
    // Types can include "sugar" in that they may refer to a
    // `typedef` which gives them a good name when printed as
    // part of diagnostic messages.
    //
    // In order to operation on types, though, we often want
    // to look past any sugar, and operate on an underlying
    // "canonical" type. The reprsentation caches a pointer to
    // a canonical type on every type, so we can easily
    // operate on the raw representation when needed.
    class ExpressionType : public Val
    {
    public:
        static RefPtr<ExpressionType> Error;
        static RefPtr<ExpressionType> initializerListType;
        static RefPtr<ExpressionType> Overloaded;

        static Dictionary<int, RefPtr<ExpressionType>> sBuiltinTypes;
        static Dictionary<String, Decl*> sMagicDecls;

        // Note: just exists to make sure we can clean up
        // canonical types we create along the way
        static List<RefPtr<ExpressionType>> sCanonicalTypes;



        static ExpressionType* GetBool();
        static ExpressionType* GetFloat();
        static ExpressionType* GetInt();
        static ExpressionType* GetUInt();
        static ExpressionType* GetVoid();
        static ExpressionType* getInitializerListType();
        static ExpressionType* GetError();

    public:
        virtual String ToString() = 0;

        bool Equals(ExpressionType * type);
        bool Equals(RefPtr<ExpressionType> type);

        bool IsVectorType() { return As<VectorExpressionType>() != nullptr; }
        bool IsArray() { return As<ArrayExpressionType>() != nullptr; }

        template<typename T>
        T* As()
        {
            return dynamic_cast<T*>(GetCanonicalType());
        }

        // Convenience/legacy wrappers for `As<>`
        ArithmeticExpressionType * AsArithmeticType() { return As<ArithmeticExpressionType>(); }
        BasicExpressionType * AsBasicType() { return As<BasicExpressionType>(); }
        VectorExpressionType * AsVectorType() { return As<VectorExpressionType>(); }
        MatrixExpressionType * AsMatrixType() { return As<MatrixExpressionType>(); }
        ArrayExpressionType * AsArrayType() { return As<ArrayExpressionType>(); }

        DeclRefType* AsDeclRefType() { return As<DeclRefType>(); }

        NamedExpressionType* AsNamedType();

        bool IsTextureOrSampler();
        bool IsTexture() { return As<TextureType>() != nullptr; }
        bool IsSampler() { return As<SamplerStateType>() != nullptr; }
        bool IsStruct();
        bool IsClass();
        static void Init();
        static void Finalize();
        ExpressionType* GetCanonicalType();

        virtual RefPtr<Val> SubstituteImpl(Substitutions* subst, int* ioDiff) override;

        virtual bool EqualsVal(Val* val) override;
    protected:
        virtual bool EqualsImpl(ExpressionType * type) = 0;

        virtual ExpressionType* CreateCanonicalType() = 0;
        ExpressionType* canonicalType = nullptr;
    };

    // A substitution represents a binding of certain
    // type-level variables to concrete argument values
    class Substitutions : public RefObject
    {
    public:
        // The generic declaration that defines the
        // parametesr we are binding to arguments
        GenericDecl*	genericDecl;

        // The actual values of the arguments
        List<RefPtr<Val>> args;

        // Any further substitutions, relating to outer generic declarations
        RefPtr<Substitutions> outer;

        // Apply a set of substitutions to the bindings in this substitution
        RefPtr<Substitutions> SubstituteImpl(Substitutions* subst, int* ioDiff);

        // Check if these are equivalent substitutiosn to another set
        bool Equals(Substitutions* subst);
        bool operator == (const Substitutions & subst)
        {
            return Equals(const_cast<Substitutions*>(&subst));
        }
        int GetHashCode() const
        {
            int rs = 0;
            for (auto && v : args)
            {
                rs ^= v->GetHashCode();
                rs *= 16777619;
            }
            return rs;
        }
    };

    class SyntaxNode : public SyntaxNodeBase
    {
    public:
        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) = 0;
    };

    class ContainerDecl;
    class SpecializeModifier;

    // Represents how much checking has been applied to a declaration.
    enum class DeclCheckState : uint8_t
    {
        // The declaration has been parsed, but not checked
        Unchecked,

        // We are in the process of checking the declaration "header"
        // (those parts of the declaration needed in order to
        // reference it)
        CheckingHeader,

        // We are done checking the declaration header.
        CheckedHeader,

        // We have checked the declaration fully.
        Checked,
    };

    // A syntax node which can have modifiers appled
    class ModifiableSyntaxNode : public SyntaxNode
    {
    public:
        Modifiers modifiers;

        template<typename T>
        FilteredModifierList<T> GetModifiersOfType() { return FilteredModifierList<T>(modifiers.first.Ptr()); }

        // Find the first modifier of a given type, or return `nullptr` if none is found.
        template<typename T>
        T* FindModifier()
        {
            return *GetModifiersOfType<T>().begin();
        }

        template<typename T>
        bool HasModifier() { return FindModifier<T>() != nullptr; }
    };

    void addModifier(
        RefPtr<ModifiableSyntaxNode>    syntax,
        RefPtr<Modifier>                modifier);


    // An intermediate type to represent either a single declaration, or a group of declarations
    class DeclBase : public ModifiableSyntaxNode
    {
    public:
    };

    class Decl : public DeclBase
    {
    public:
        ContainerDecl*  ParentDecl = nullptr;

        Token Name;
        String const& getName() { return Name.Content; }
        Token const& getNameToken() { return Name; }


        DeclCheckState checkState = DeclCheckState::Unchecked;

        // The next declaration defined in the same container with the same name
        Decl* nextInContainerWithSameName = nullptr;

        bool IsChecked(DeclCheckState state) { return checkState >= state; }
        void SetCheckState(DeclCheckState state)
        {
            assert(state >= checkState);
            checkState = state;
        }
    };

    struct QualType
    {
        RefPtr<ExpressionType>	type;
        bool					IsLeftValue;

        QualType()
            : IsLeftValue(false)
        {}

        QualType(RefPtr<ExpressionType> type)
            : type(type)
            , IsLeftValue(false)
        {}

        QualType(ExpressionType* type)
            : type(type)
            , IsLeftValue(false)
        {}

        void operator=(RefPtr<ExpressionType> t)
        {
            *this = QualType(t);
        }

        void operator=(ExpressionType* t)
        {
            *this = QualType(t);
        }

        ExpressionType* Ptr() { return type.Ptr(); }

        operator RefPtr<ExpressionType>() { return type; }
        RefPtr<ExpressionType> operator->() { return type; }
    };

    class ExpressionSyntaxNode : public SyntaxNode
    {
    public:
        QualType Type;
        ExpressionSyntaxNode()
        {}
    };




    // A reference to a declaration, which may include
    // substitutions for generic parameters.
    struct DeclRefBase
    {
        typedef Decl DeclType;

        // The underlying declaration
        Decl* decl = nullptr;
        Decl* getDecl() const { return decl; }

        // Optionally, a chain of substititions to perform
        RefPtr<Substitutions> substitutions;

        DeclRefBase()
        {}

        DeclRefBase(Decl* decl, RefPtr<Substitutions> substitutions)
            : decl(decl)
            , substitutions(substitutions)
        {}

        // Apply substitutions to a type or ddeclaration
        RefPtr<ExpressionType> Substitute(RefPtr<ExpressionType> type) const;

        DeclRefBase Substitute(DeclRefBase declRef) const;

        // Apply substitutions to an expression
        RefPtr<ExpressionSyntaxNode> Substitute(RefPtr<ExpressionSyntaxNode> expr) const;

        // Apply substitutions to this declaration reference
        DeclRefBase SubstituteImpl(Substitutions* subst, int* ioDiff);

        // Check if this is an equivalent declaration reference to another
        bool Equals(DeclRefBase const& declRef) const;
        bool operator == (const DeclRefBase& other) const
        {
            return Equals(other);
        }

        // Convenience accessors for common properties of declarations
        String const& GetName() const;
        DeclRefBase GetParent() const;

        int GetHashCode() const;
    };

    template<typename T>
    struct DeclRef : DeclRefBase
    {
        typedef T DeclType;

        DeclRef()
        {}

        DeclRef(T* decl, RefPtr<Substitutions> substitutions)
            : DeclRefBase(decl, substitutions)
        {}

        template <typename U>
        DeclRef(DeclRef<U> const& other,
            typename EnableIf<IsConvertible<T*, U*>::Value, void>::type* = 0)
            : DeclRefBase(other.decl, other.substitutions)
        {
        }

        // "dynamic cast" to a more specific declaration reference type
        template<typename T>
        DeclRef<T> As() const
        {
            DeclRef<T> result;
            result.decl = dynamic_cast<T*>(decl);
            result.substitutions = substitutions;
            return result;
        }

        T* getDecl() const
        {
            return (T*)decl;
        }

        operator T*() const
        {
            return getDecl();
        }

        //
        static DeclRef<T> unsafeInit(DeclRefBase const& declRef)
        {
            return DeclRef<T>((T*) declRef.decl, declRef.substitutions);
        }

        RefPtr<ExpressionType> Substitute(RefPtr<ExpressionType> type) const
        {
            return DeclRefBase::Substitute(type);
        }
        RefPtr<ExpressionSyntaxNode> Substitute(RefPtr<ExpressionSyntaxNode> expr) const
        {
            return DeclRefBase::Substitute(expr);
        }

        // Apply substitutions to a type or ddeclaration
        template<typename U>
        DeclRef<U> Substitute(DeclRef<U> declRef) const
        {
            return DeclRef<U>::unsafeInit(DeclRefBase::Substitute(declRef));
        }

        // Apply substitutions to this declaration reference
        DeclRef<T> SubstituteImpl(Substitutions* subst, int* ioDiff)
        {
            return DeclRef<T>::unsafeInit(DeclRefBase::SubstituteImpl(subst, ioDiff));
        }

        DeclRef<ContainerDecl> GetParent() const
        {
            return DeclRef<ContainerDecl>::unsafeInit(DeclRefBase::GetParent());
        }

    };

    // The type of a reference to an overloaded name
    class OverloadGroupType : public ExpressionType
    {
    public:
        virtual String ToString() override;

    protected:
        virtual bool EqualsImpl(ExpressionType * type) override;
        virtual ExpressionType* CreateCanonicalType() override;
        virtual int GetHashCode() override;
    };

    // The type of an initializer-list expression (before it has
    // been coerced to some other type)
    class InitializerListType : public ExpressionType
    {
    public:
        virtual String ToString() override;

    protected:
        virtual bool EqualsImpl(ExpressionType * type) override;
        virtual ExpressionType* CreateCanonicalType() override;
        virtual int GetHashCode() override;
    };

    // The type of an expression that was erroneous
    class ErrorType : public ExpressionType
    {
    public:
        virtual String ToString() override;

    protected:
        virtual bool EqualsImpl(ExpressionType * type) override;
        virtual ExpressionType* CreateCanonicalType() override;
        virtual int GetHashCode() override;
    };

    // A type that takes the form of a reference to some declaration
    class DeclRefType : public ExpressionType
    {
    public:
        DeclRef<Decl> declRef;

        virtual String ToString() override;
        virtual RefPtr<Val> SubstituteImpl(Substitutions* subst, int* ioDiff) override;

        static DeclRefType* Create(DeclRef<Decl> declRef);

    protected:
        DeclRefType()
        {}
        DeclRefType(DeclRef<Decl> declRef)
            : declRef(declRef)
        {}
        virtual int GetHashCode() override;
        virtual bool EqualsImpl(ExpressionType * type) override;
        virtual ExpressionType* CreateCanonicalType() override;
    };

    // Base class for types that can be used in arithmetic expressions
    class ArithmeticExpressionType : public DeclRefType
    {
    public:
        virtual BasicExpressionType* GetScalarType() = 0;
    };

    class FunctionDeclBase;

    class BasicExpressionType : public ArithmeticExpressionType
    {
    public:
        BaseType BaseType;

        BasicExpressionType()
        {
            BaseType = Slang::BaseType::Int;
        }
        BasicExpressionType(Slang::BaseType baseType)
        {
            BaseType = baseType;
        }
        virtual Slang::String ToString() override;
    protected:
        virtual BasicExpressionType* GetScalarType() override;
        virtual bool EqualsImpl(ExpressionType * type) override;
        virtual ExpressionType* CreateCanonicalType() override;
    };


    class TextureTypeBase : public DeclRefType
    {
    public:
        // The type that results from fetching an element from this texture
        RefPtr<ExpressionType> elementType;

        // Bits representing the kind of texture type we are looking at
        // (e.g., `Texture2DMS` vs. `TextureCubeArray`)
        typedef uint16_t Flavor;
        Flavor flavor;

        enum
        {
            // Mask for the overall "shape" of the texture
            ShapeMask		= SLANG_RESOURCE_BASE_SHAPE_MASK,

            // Flag for whether the shape has "array-ness"
            ArrayFlag		= SLANG_TEXTURE_ARRAY_FLAG,

            // Whether or not the texture stores multiple samples per pixel
            MultisampleFlag	= SLANG_TEXTURE_MULTISAMPLE_FLAG,

            // Whether or not this is a shadow texture
            //
            // TODO(tfoley): is this even meaningful/used?
            // ShadowFlag		= 0x80, 
        };

        enum Shape : uint8_t
        {
            Shape1D			= SLANG_TEXTURE_1D,
            Shape2D			= SLANG_TEXTURE_2D,
            Shape3D			= SLANG_TEXTURE_3D,
            ShapeCube		= SLANG_TEXTURE_CUBE,

            Shape1DArray	= Shape1D | ArrayFlag,
            Shape2DArray	= Shape2D | ArrayFlag,
            // No Shape3DArray
            ShapeCubeArray	= ShapeCube | ArrayFlag,
        };
            

        Shape GetBaseShape() const { return Shape(flavor & ShapeMask); }
        bool isArray() const { return (flavor & ArrayFlag) != 0; }
        bool isMultisample() const { return (flavor & MultisampleFlag) != 0; }
//            bool isShadow() const { return (flavor & ShadowFlag) != 0; }

        SlangResourceShape getShape() const { return flavor & 0xFF; }
        SlangResourceAccess getAccess() const { return (flavor >> 8) & 0xFF; }

        TextureTypeBase(
            Flavor flavor,
            RefPtr<ExpressionType> elementType)
            : elementType(elementType)
            , flavor(flavor)
        {}
    };

    class TextureType : public TextureTypeBase
    {
    public:
        TextureType(
            Flavor flavor,
            RefPtr<ExpressionType> elementType)
            : TextureTypeBase(flavor, elementType)
        {}
    };

    // This is a base type for texture/sampler pairs,
    // as they exist in, e.g., GLSL
    class TextureSamplerType : public TextureTypeBase
    {
    public:
        TextureSamplerType(
            Flavor flavor,
            RefPtr<ExpressionType> elementType)
            : TextureTypeBase(flavor, elementType)
        {}
    };

    // This is a base type for `image*` types, as they exist in GLSL
    class GLSLImageType : public TextureTypeBase
    {
    public:
        GLSLImageType(
            Flavor flavor,
            RefPtr<ExpressionType> elementType)
            : TextureTypeBase(flavor, elementType)
        {}
    };

    class SamplerStateType : public DeclRefType
    {
    public:
        // What flavor of sampler state is this
        enum class Flavor : uint8_t
        {
            SamplerState,
            SamplerComparisonState,
        };
        Flavor flavor;
    };

    // Other cases of generic types known to the compiler
    class BuiltinGenericType : public DeclRefType
    {
    public:
        RefPtr<ExpressionType> elementType;
    };

    // Types that behave like pointers, in that they can be
    // dereferenced (implicitly) to access members defined
    // in the element type.
    class PointerLikeType : public BuiltinGenericType
    {};

    // Generic types used in existing Slang code
    // TODO(tfoley): check that these are actually working right...
    class PatchType : public PointerLikeType {};
    class StorageBufferType : public BuiltinGenericType {};
    class UniformBufferType : public PointerLikeType {};
    class PackedBufferType : public BuiltinGenericType {};

    // HLSL buffer-type resources

    class HLSLBufferType : public BuiltinGenericType {};
    class HLSLRWBufferType : public BuiltinGenericType {};
    class HLSLStructuredBufferType : public BuiltinGenericType {};
    class HLSLRWStructuredBufferType : public BuiltinGenericType {};

    class UntypedBufferResourceType : public DeclRefType {};
    class HLSLByteAddressBufferType : public UntypedBufferResourceType {};
    class HLSLRWByteAddressBufferType : public UntypedBufferResourceType {};

    class HLSLAppendStructuredBufferType : public BuiltinGenericType {};
    class HLSLConsumeStructuredBufferType : public BuiltinGenericType {};

    class HLSLPatchType : public DeclRefType
    {
    public:
        ExpressionType* getElementType();
        IntVal*         getElementCount();
    };

    class HLSLInputPatchType : public HLSLPatchType {};
    class HLSLOutputPatchType : public HLSLPatchType {};

    // HLSL geometry shader output stream types

    class HLSLStreamOutputType : public BuiltinGenericType {};
    class HLSLPointStreamType : public HLSLStreamOutputType {};
    class HLSLLineStreamType : public HLSLStreamOutputType {};
    class HLSLTriangleStreamType : public HLSLStreamOutputType {};

    //
    class GLSLInputAttachmentType : public DeclRefType {};

    // Base class for types used when desugaring parameter block
    // declarations, includeing HLSL `cbuffer` or GLSL `uniform` blocks.
    class ParameterBlockType : public PointerLikeType {};

    class UniformParameterBlockType : public ParameterBlockType {};
    class VaryingParameterBlockType : public ParameterBlockType {};

    // Type for HLSL `cbuffer` declarations, and `ConstantBuffer<T>`
    // ALso used for GLSL `uniform` blocks.
    class ConstantBufferType : public UniformParameterBlockType {};

    // Type for HLSL `tbuffer` declarations, and `TextureBuffer<T>`
    class TextureBufferType : public UniformParameterBlockType {};

    // Type for GLSL `in` and `out` blocks
    class GLSLInputParameterBlockType : public VaryingParameterBlockType {};
    class GLSLOutputParameterBlockType : public VaryingParameterBlockType {};

    // Type for GLLSL `buffer` blocks
    class GLSLShaderStorageBufferType : public UniformParameterBlockType {};

    class ArrayExpressionType : public ExpressionType
    {
    public:
        RefPtr<ExpressionType> BaseType;
        RefPtr<IntVal> ArrayLength;
        virtual Slang::String ToString() override;
    protected:
        virtual bool EqualsImpl(ExpressionType * type) override;
        virtual ExpressionType* CreateCanonicalType() override;
        virtual int GetHashCode() override;
    };

    // The "type" of an expression that resolves to a type.
    // For example, in the expression `float(2)` the sub-expression,
    // `float` would have the type `TypeType(float)`.
    class TypeType : public ExpressionType
    {
    public:
        TypeType(RefPtr<ExpressionType> type)
            : type(type)
        {}

        // The type that this is the type of...
        RefPtr<ExpressionType> type;


        virtual String ToString() override;

    protected:
        virtual bool EqualsImpl(ExpressionType * type) override;
        virtual ExpressionType* CreateCanonicalType() override;
        virtual int GetHashCode() override;
    };

    class GenericDecl;

    // A vector type, e.g., `vector<T,N>`
    class VectorExpressionType : public ArithmeticExpressionType
    {
    public:
#if 0
        VectorExpressionType(
            RefPtr<ExpressionType>	elementType,
            RefPtr<IntVal>			elementCount)
            : elementType(elementType)
            , elementCount(elementCount)
        {}
#endif

        // The type of vector elements.
        // As an invariant, this should be a basic type or an alias.
        RefPtr<ExpressionType>	elementType;

        // The number of elements
        RefPtr<IntVal>			elementCount;

        virtual String ToString() override;

    protected:
        virtual BasicExpressionType* GetScalarType() override;
    };

    // A matrix type, e.g., `matrix<T,R,C>`
    class MatrixExpressionType : public ArithmeticExpressionType
    {
    public:
        // TODO: consider adding these back for convenience,
        // with a way to initialize them on-demand from the
        // real storage (which is in the `DeclRefType`
#if 0
        // The type of vector elements.
        // As an invariant, this should be a basic type or an alias.
        RefPtr<ExpressionType>			elementType;

        // The type of the matrix rows
        RefPtr<VectorExpressionType>	rowType;

        // The number of rows and columns
        RefPtr<IntVal>					rowCount;
        RefPtr<IntVal>					colCount;
#endif
        ExpressionType* getElementType();
        IntVal*         getRowCount();
        IntVal*         getColumnCount();


        virtual String ToString() override;

    protected:
        virtual BasicExpressionType* GetScalarType() override;
    };

    inline BaseType GetVectorBaseType(VectorExpressionType* vecType) {
        return vecType->elementType->AsBasicType()->BaseType;
    }

    inline int GetVectorSize(VectorExpressionType* vecType)
    {
        auto constantVal = vecType->elementCount.As<ConstantIntVal>();
        if (constantVal)
            return constantVal->value;
        // TODO: what to do in this case?
        return 0;
    }

    class ContainerDecl;


    // A group of declarations that should be treated as a unit
    class DeclGroup : public DeclBase
    {
    public:
        List<RefPtr<Decl>> decls;

        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    template<typename T>
    struct FilteredMemberList
    {
        typedef RefPtr<Decl> Element;

        FilteredMemberList()
            : mBegin(NULL)
            , mEnd(NULL)
        {}

        explicit FilteredMemberList(
            List<Element> const& list)
            : mBegin(Adjust(list.begin(), list.end()))
            , mEnd(list.end())
        {}

        struct Iterator
        {
            Element* mCursor;
            Element* mEnd;

            bool operator!=(Iterator const& other)
            {
                return mCursor != other.mCursor;
            }

            void operator++()
            {
                mCursor = Adjust(mCursor + 1, mEnd);
            }

            RefPtr<T>& operator*()
            {
                return *(RefPtr<T>*)mCursor;
            }
        };

        Iterator begin()
        {
            Iterator iter = { mBegin, mEnd };
            return iter;
        }

        Iterator end()
        {
            Iterator iter = { mEnd, mEnd };
            return iter;
        }

        static Element* Adjust(Element* cursor, Element* end)
        {
            while (cursor != end)
            {
                if ((*cursor).As<T>())
                    return cursor;
                cursor++;
            }
            return cursor;
        }

        // TODO(tfoley): It is ugly to have these.
        // We should probably fix the call sites instead.
        RefPtr<T>& First() { return *begin(); }
        int Count()
        {
            int count = 0;
            for (auto iter : (*this))
            {
                (void)iter;
                count++;
            }
            return count;
        }

        List<RefPtr<T>> ToArray()
        {
            List<RefPtr<T>> result;
            for (auto element : (*this))
            {
                result.Add(element);
            }
            return result;
        }

        Element* mBegin;
        Element* mEnd;
    };

    struct TransparentMemberInfo
    {
        // The declaration of the transparent member
        Decl*	decl;
    };

    // A "container" decl is a parent to other declarations
    class ContainerDecl : public Decl
    {
    public:
        List<RefPtr<Decl>> Members;

        template<typename T>
        FilteredMemberList<T> getMembersOfType()
        {
            return FilteredMemberList<T>(Members);
        }


        // Dictionary for looking up members by name.
        // This is built on demand before performing lookup.
        Dictionary<String, Decl*> memberDictionary;

        // Whether the `memberDictionary` is valid.
        // Should be set to `false` if any members get added/remoed.
        bool memberDictionaryIsValid = false;

        // A list of transparent members, to be used in lookup
        // Note: this is only valid if `memberDictionaryIsValid` is true
        List<TransparentMemberInfo> transparentMembers;
    };

    template<typename T>
    struct FilteredMemberRefList
    {
        List<RefPtr<Decl>> const&	decls;
        RefPtr<Substitutions>		substitutions;

        FilteredMemberRefList(
            List<RefPtr<Decl>> const&	decls,
            RefPtr<Substitutions>		substitutions)
            : decls(decls)
            , substitutions(substitutions)
        {}

        int Count() const
        {
            int count = 0;
            for (auto d : *this)
                count++;
            return count;
        }

        List<DeclRef<T>> ToArray() const
        {
            List<DeclRef<T>> result;
            for (auto d : *this)
                result.Add(d);
            return result;
        }

        struct Iterator
        {
            FilteredMemberRefList const* list;
            RefPtr<Decl>* ptr;
            RefPtr<Decl>* end;

            Iterator() : list(nullptr), ptr(nullptr) {}
            Iterator(
                FilteredMemberRefList const* list,
                RefPtr<Decl>* ptr,
                RefPtr<Decl>* end)
                : list(list)
                , ptr(ptr)
                , end(end)
            {}

            bool operator!=(Iterator other)
            {
                return ptr != other.ptr;
            }

            void operator++()
            {
                ptr = list->Adjust(ptr + 1, end);
            }

            DeclRef<T> operator*()
            {
                return DeclRef<T>((T*) ptr->Ptr(), list->substitutions);
            }
        };

        Iterator begin() const { return Iterator(this, Adjust(decls.begin(), decls.end()), decls.end()); }
        Iterator end() const { return Iterator(this, decls.end(), decls.end()); }

        RefPtr<Decl>* Adjust(RefPtr<Decl>* ptr, RefPtr<Decl>* end) const
        {
            while (ptr != end)
            {
                DeclRef<Decl> declRef(ptr->Ptr(), substitutions);
                if (declRef.As<T>())
                    return ptr;
                ptr++;
            }
            return end;
        }
    };

    inline FilteredMemberRefList<Decl> getMembers(DeclRef<ContainerDecl> const& declRef)
    {
        return FilteredMemberRefList<Decl>(declRef.getDecl()->Members, declRef.substitutions);
    }

    template<typename T>
    inline FilteredMemberRefList<T> getMembersOfType(DeclRef<ContainerDecl> const& declRef)
    {
        return FilteredMemberRefList<T>(declRef.getDecl()->Members, declRef.substitutions);
    }

    //
    // Type Expressions
    //

    // A "type expression" is a term that we expect to resolve to a type during checking.
    // We store both the original syntax and the resolved type here.
    struct TypeExp
    {
        TypeExp() {}
        TypeExp(TypeExp const& other)
            : exp(other.exp)
            , type(other.type)
        {}
        explicit TypeExp(RefPtr<ExpressionSyntaxNode> exp)
            : exp(exp)
        {}
        TypeExp(RefPtr<ExpressionSyntaxNode> exp, RefPtr<ExpressionType> type)
            : exp(exp)
            , type(type)
        {}

        RefPtr<ExpressionSyntaxNode> exp;
        RefPtr<ExpressionType> type;

        bool Equals(ExpressionType* other) {
            return type->Equals(other);
        }
        bool Equals(RefPtr<ExpressionType> other) {
            return type->Equals(other.Ptr());
        }
        ExpressionType* Ptr() { return type.Ptr(); }
        operator RefPtr<ExpressionType>()
        {
            return type;
        }
        ExpressionType* operator->() { return Ptr(); }

        TypeExp Accept(SyntaxVisitor* visitor);
    };


    //
    // Declarations
    //

    // Base class for all variable-like declarations
    class VarDeclBase : public Decl
    {
    public:
        // Type of the variable
        TypeExp Type;

        ExpressionType* getType() { return Type.type.Ptr(); }

        // Initializer expression (optional)
        RefPtr<ExpressionSyntaxNode> Expr;
    };

    inline RefPtr<ExpressionType> GetType(DeclRef<VarDeclBase> const& declRef)
    {
        return declRef.Substitute(declRef.getDecl()->Type);
    }

    inline RefPtr<ExpressionSyntaxNode> getInitExpr(DeclRef<VarDeclBase> const& declRef)
    {
        return declRef.Substitute(declRef.getDecl()->Expr);
    }

    // A field of a `struct` type
    class StructField : public VarDeclBase
    {
    public:
        StructField()
        {}
        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    // An `AggTypeDeclBase` captures the shared functionality
    // between true aggregate type declarations and extension
    // declarations:
    //
    // - Both can container members (they are `ContainerDecl`s)
    // - Both can have declared bases
    // - Both expose a `this` variable in their body
    //
    class AggTypeDeclBase : public ContainerDecl
    {
    public:
    };

    // An extension to apply to an existing type
    class ExtensionDecl : public AggTypeDeclBase
    {
    public:
        TypeExp targetType;

        // next extension attached to the same nominal type
        ExtensionDecl* nextCandidateExtension = nullptr;


        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };


    inline RefPtr<ExpressionType> GetTargetType(DeclRef<ExtensionDecl> const& declRef)
    {
        return declRef.Substitute(declRef.getDecl()->targetType);
    }

    // Declaration of a type that represents some sort of aggregate
    class AggTypeDecl : public AggTypeDeclBase
    {
    public:

        // extensions that might apply to this declaration
        ExtensionDecl* candidateExtensions = nullptr;
        FilteredMemberList<StructField> GetFields()
        {
            return getMembersOfType<StructField>();
        }
        StructField* FindField(String name)
        {
            for (auto field : GetFields())
            {
                if (field->Name.Content == name)
                    return field.Ptr();
            }
            return nullptr;
        }
        int FindFieldIndex(String name)
        {
            int index = 0;
            for (auto field : GetFields())
            {
                if (field->Name.Content == name)
                    return index;
                index++;
            }
            return -1;
        }
    };

    inline ExtensionDecl* GetCandidateExtensions(DeclRef<AggTypeDecl> const& declRef)
    {
        return declRef.getDecl()->candidateExtensions;
    }

    class StructSyntaxNode : public AggTypeDecl
    {
    public:
        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    inline FilteredMemberRefList<StructField> GetFields(DeclRef<StructSyntaxNode> const& declRef)
    {
        return getMembersOfType<StructField>(declRef);
    }

    class ClassSyntaxNode : public AggTypeDecl
    {
    public:
        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    // An interface which other types can conform to
    class InterfaceDecl : public AggTypeDecl
    {
    public:
        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    // A kind of pseudo-member that represents an explicit
    // or implicit inheritance relationship.
    //
    class InheritanceDecl : public Decl
    {
    public:
        // The type expression as written
        TypeExp base;

        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    inline RefPtr<ExpressionType> getBaseType(DeclRef<InheritanceDecl> const& declRef)
    {
        return declRef.Substitute(declRef.getDecl()->base.type);
    }

    // TODO: may eventually need sub-classes for explicit/direct vs. implicit/indirect inheritance


    // A declaration that represents a simple (non-aggregate) type
    class SimpleTypeDecl : public Decl
    {
    };

    // A `typedef` declaration
    class TypeDefDecl : public SimpleTypeDecl
    {
    public:
        TypeExp Type;

        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    inline RefPtr<ExpressionType> GetType(DeclRef<TypeDefDecl> const& declRef)
    {
        return declRef.Substitute(declRef.getDecl()->Type);
    }

    // A type alias of some kind (e.g., via `typedef`)
    class NamedExpressionType : public ExpressionType
    {
    public:
        NamedExpressionType(DeclRef<TypeDefDecl> declRef)
            : declRef(declRef)
        {}

        DeclRef<TypeDefDecl> declRef;

        virtual String ToString() override;

    protected:
        virtual bool EqualsImpl(ExpressionType * type) override;
        virtual ExpressionType* CreateCanonicalType() override;
        virtual int GetHashCode() override;
    };


    class StatementSyntaxNode : public ModifiableSyntaxNode
    {
    public:
    };

    // A scope for local declarations (e.g., as part of a statement)
    class ScopeDecl : public ContainerDecl
    {
    public:
        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    class ScopeStmt : public StatementSyntaxNode
    {
    public:
        RefPtr<ScopeDecl> scopeDecl;
    };

    class BlockStatementSyntaxNode : public ScopeStmt
    {
    public:
        List<RefPtr<StatementSyntaxNode>> Statements;
        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    class UnparsedStmt : public StatementSyntaxNode
    {
    public:
        // The tokens that were contained between `{` and `}`
        List<Token> tokens;

        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    class ParameterSyntaxNode : public VarDeclBase
    {
    public:
        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    // Base class for things that have parameter lists and can thus be applied to arguments ("called")
    class CallableDecl : public ContainerDecl
    {
    public:
        FilteredMemberList<ParameterSyntaxNode> GetParameters()
        {
            return getMembersOfType<ParameterSyntaxNode>();
        }
        TypeExp ReturnType;
    };

    inline RefPtr<ExpressionType> GetResultType(DeclRef<CallableDecl> const& declRef)
    {
        return declRef.Substitute(declRef.getDecl()->ReturnType.type.Ptr());
    }

    inline FilteredMemberRefList<ParameterSyntaxNode> GetParameters(DeclRef<CallableDecl> const& declRef)
    {
        return getMembersOfType<ParameterSyntaxNode>(declRef);
    }

    // Base class for callable things that may also have a body that is evaluated to produce their result
    class FunctionDeclBase : public CallableDecl
    {
    public:
        RefPtr<StatementSyntaxNode> Body;
    };

    // Function types are currently used for references to symbols that name
    // either ordinary functions, or "component functions."
    // We do not directly store a representation of the type, and instead
    // use a reference to the symbol to stand in for its logical type
    class FuncType : public ExpressionType
    {
    public:
        DeclRef<CallableDecl> declRef;

        virtual String ToString() override;
    protected:
        virtual bool EqualsImpl(ExpressionType * type) override;
        virtual ExpressionType* CreateCanonicalType() override;
        virtual int GetHashCode() override;
    };

    // A constructor/initializer to create instances of a type
    class ConstructorDecl : public FunctionDeclBase
    {
    public:
        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    // A subscript operation used to index instances of a type
    class SubscriptDecl : public CallableDecl
    {
    public:
        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    // An "accessor" for a subscript or property
    class AccessorDecl : public FunctionDeclBase
    {
    public:
        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    class GetterDecl : public AccessorDecl
    {
    };

    class SetterDecl : public AccessorDecl
    {
    };

    //

    class FunctionSyntaxNode : public FunctionDeclBase
    {
    public:
        String InternalName;
        bool IsInline() { return HasModifier<InlineModifier>(); }
        bool IsExtern() { return HasModifier<ExternModifier>(); }
        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
        FunctionSyntaxNode()
        {
        }
    };

    struct Scope : public RefObject
    {
        // The parent of this scope (where lookup should go if nothing is found locally)
        RefPtr<Scope>           parent;

        // The next sibling of this scope (a peer for lookup)
        RefPtr<Scope>           nextSibling;

        // The container to use for lookup
        //
        // Note(tfoley): This is kept as an unowned pointer
        // so that a scope can't keep parts of the AST alive,
        // but the opposite it allowed.
        ContainerDecl*          containerDecl;
    };

    // Base class for expressions that will reference declarations
    class DeclRefExpr : public ExpressionSyntaxNode
    {
    public:
        // The scope in which to perform lookup
        RefPtr<Scope>   scope;

        // The declaration of the symbol being referenced
        DeclRef<Decl> declRef;

        // The name of the symbol being referenced
        String name;
    };

    class VarExpressionSyntaxNode : public DeclRefExpr
    {
    public:
        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    // Masks to be applied when lookup up declarations
    enum class LookupMask : uint8_t
    {
        Type = 0x1,
        Function = 0x2,
        Value = 0x4,

        All = Type | Function | Value,
    };

    // Represents one item found during lookup
    struct LookupResultItem
    {
        // Sometimes lookup finds an item, but there were additional
        // "hops" taken to reach it. We need to remember these steps
        // so that if/when we consturct a full expression we generate
        // appropriate AST nodes for all the steps.
        //
        // We build up a list of these "breadcrumbs" while doing
        // lookup, and store them alongside each item found.
        class Breadcrumb : public RefObject
        {
        public:
            enum class Kind
            {
                Member, // A member was references
                Deref, // A value with pointer(-like) type was dereferenced
            };

            Kind kind;
            DeclRef<Decl> declRef;
            RefPtr<Breadcrumb> next;

            Breadcrumb(Kind kind, DeclRef<Decl> declRef, RefPtr<Breadcrumb> next)
                : kind(kind)
                , declRef(declRef)
                , next(next)
            {}
        };

        // A properly-specialized reference to the declaration that was found.
        DeclRef<Decl> declRef;

        // Any breadcrumbs needed in order to turn that declaration
        // reference into a well-formed expression.
        //
        // This is unused in the simple case where a declaration
        // is being referenced directly (rather than through
        // transparent members).
        RefPtr<Breadcrumb> breadcrumbs;

        LookupResultItem() = default;
        explicit LookupResultItem(DeclRef<Decl> declRef)
            : declRef(declRef)
        {}
        LookupResultItem(DeclRef<Decl> declRef, RefPtr<Breadcrumb> breadcrumbs)
            : declRef(declRef)
            , breadcrumbs(breadcrumbs)
        {}
    };


    // Result of looking up a name in some lexical/semantic environment.
    // Can be used to enumerate all the declarations matching that name,
    // in the case where the result is overloaded.
    struct LookupResult
    {
        // The one item that was found, in the smple case
        LookupResultItem item;

        // All of the items that were found, in the complex case.
        // Note: if there was no overloading, then this list isn't
        // used at all, to avoid allocation.
        List<LookupResultItem> items;

        // Was at least one result found?
        bool isValid() const { return item.declRef.getDecl() != nullptr; }

        bool isOverloaded() const { return items.Count() > 1; }
    };

    class SemanticsVisitor;

    struct LookupRequest
    {
        SemanticsVisitor*   semantics   = nullptr;

        RefPtr<Scope>       scope       = nullptr;
        RefPtr<Scope>       endScope    = nullptr;

        LookupMask          mask        = LookupMask::All;
    };

    // An expression that references an overloaded set of declarations
    // having the same name.
    class OverloadedExpr : public ExpressionSyntaxNode
    {
    public:
        // Optional: the base expression is this overloaded result
        // arose from a member-reference expression.
        RefPtr<ExpressionSyntaxNode> base;

        // The lookup result that was ambiguous
        LookupResult lookupResult2;

        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    typedef double FloatingPointLiteralValue;

    class ConstantExpressionSyntaxNode : public ExpressionSyntaxNode
    {
    public:
        enum class ConstantType
        {
            Int, Bool, Float
        };
        ConstantType ConstType;
        union
        {
            int IntValue;
            FloatingPointLiteralValue FloatValue;
        };
        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    enum class Operator
    {
        Neg, Not, BitNot, PreInc, PreDec, PostInc, PostDec,
        Mul, Div, Mod,
        Add, Sub,
        Lsh, Rsh,
        Eql, Neq, Greater, Less, Geq, Leq,
        BitAnd, BitXor, BitOr,
        And,
        Or,
        Sequence,
        Select,
        Assign = 200, AddAssign, SubAssign, MulAssign, DivAssign, ModAssign,
        LshAssign, RshAssign, OrAssign, AndAssign, XorAssign,
    };
    String GetOperatorFunctionName(Operator op);
    String OperatorToString(Operator op);

    // An initializer list, e.g. `{ 1, 2, 3 }`
    class InitializerListExpr : public ExpressionSyntaxNode
    {
    public:
        List<RefPtr<ExpressionSyntaxNode>> args;

        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    // A base expression being applied to arguments: covers
    // both ordinary `()` function calls and `<>` generic application
    class AppExprBase : public ExpressionSyntaxNode
    {
    public:
        RefPtr<ExpressionSyntaxNode> FunctionExpr;
        List<RefPtr<ExpressionSyntaxNode>> Arguments;
    };


    class InvokeExpressionSyntaxNode : public AppExprBase
    {
    public:
        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    class OperatorExpressionSyntaxNode : public InvokeExpressionSyntaxNode
    {
    public:
//            Operator Operator;
//            void SetOperator(RefPtr<Scope> scope, Slang::Operator op);
        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    class InfixExpr   : public OperatorExpressionSyntaxNode {};
    class PrefixExpr  : public OperatorExpressionSyntaxNode {};
    class PostfixExpr : public OperatorExpressionSyntaxNode {};

    class IndexExpressionSyntaxNode : public ExpressionSyntaxNode
    {
    public:
        RefPtr<ExpressionSyntaxNode> BaseExpression;
        RefPtr<ExpressionSyntaxNode> IndexExpression;
        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    class MemberExpressionSyntaxNode : public DeclRefExpr
    {
    public:
        RefPtr<ExpressionSyntaxNode> BaseExpression;
        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    class SwizzleExpr : public ExpressionSyntaxNode
    {
    public:
        RefPtr<ExpressionSyntaxNode> base;
        int elementCount;
        int elementIndices[4];

        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    // A dereference of a pointer or pointer-like type
    class DerefExpr : public ExpressionSyntaxNode
    {
    public:
        RefPtr<ExpressionSyntaxNode> base;

        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    class TypeCastExpressionSyntaxNode : public ExpressionSyntaxNode
    {
    public:
        TypeExp TargetType;
        RefPtr<ExpressionSyntaxNode> Expression;
        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    class SelectExpressionSyntaxNode : public OperatorExpressionSyntaxNode
    {
    public:
    };


    class EmptyStatementSyntaxNode : public StatementSyntaxNode
    {
    public:
        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    class DiscardStatementSyntaxNode : public StatementSyntaxNode
    {
    public:
        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    struct Variable : public VarDeclBase
    {
        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    class VarDeclrStatementSyntaxNode : public StatementSyntaxNode
    {
    public:
        RefPtr<DeclBase> decl;
        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    // A "module" of code (essentiately, a single translation unit)
    // that provides a scope for some number of declarations.
    class ProgramSyntaxNode : public ContainerDecl
    {
    public:
        // Access members of specific types
        FilteredMemberList<FunctionSyntaxNode> GetFunctions()
        {
            return getMembersOfType<FunctionSyntaxNode>();
        }

        FilteredMemberList<ClassSyntaxNode> GetClasses()
        {
            return getMembersOfType<ClassSyntaxNode>();
        }
        FilteredMemberList<StructSyntaxNode> GetStructs()
        {
            return getMembersOfType<StructSyntaxNode>();
        }
        FilteredMemberList<TypeDefDecl> GetTypeDefs()
        {
            return getMembersOfType<TypeDefDecl>();
        }

        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

            class ImportDecl : public Decl
    {
    public:
        // The name of the module we are trying to import
        Token nameToken;

        // The scope that we want to import into
        RefPtr<Scope> scope;

        // The module that actually got imported
        RefPtr<ProgramSyntaxNode>   importedModuleDecl;

        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };


    class IfStatementSyntaxNode : public StatementSyntaxNode
    {
    public:
        RefPtr<ExpressionSyntaxNode> Predicate;
        RefPtr<StatementSyntaxNode> PositiveStatement;
        RefPtr<StatementSyntaxNode> NegativeStatement;
        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    // A statement that can be escaped with a `break`
    class BreakableStmt : public ScopeStmt
    {};

    class SwitchStmt : public BreakableStmt
    {
    public:
        RefPtr<ExpressionSyntaxNode> condition;
        RefPtr<StatementSyntaxNode> body;

        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    // A statement that is expected to appear lexically nested inside
    // some other construct, and thus needs to keep track of the
    // outer statement that it is associated with...
    class ChildStmt : public StatementSyntaxNode
    {
    public:
        StatementSyntaxNode* parentStmt = nullptr;
    };

    // a `case` or `default` statement inside a `switch`
    //
    // Note(tfoley): A correct AST for a C-like language would treat
    // these as a labelled statement, and so they would contain a
    // sub-statement. I'm leaving that out for now for simplicity.
    class CaseStmtBase : public ChildStmt
    {
    public:
    };

    // a `case` statement inside a `switch`
    class CaseStmt : public CaseStmtBase
    {
    public:
        RefPtr<ExpressionSyntaxNode> expr;

        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    // a `default` statement inside a `switch`
    class DefaultStmt : public CaseStmtBase
    {
    public:
        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    // A statement that represents a loop, and can thus be escaped with a `continue`
    class LoopStmt : public BreakableStmt
    {};

    class ForStatementSyntaxNode : public LoopStmt
    {
    public:
        RefPtr<StatementSyntaxNode> InitialStatement;
        RefPtr<ExpressionSyntaxNode> SideEffectExpression, PredicateExpression;
        RefPtr<StatementSyntaxNode> Statement;
        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    class WhileStatementSyntaxNode : public LoopStmt
    {
    public:
        RefPtr<ExpressionSyntaxNode> Predicate;
        RefPtr<StatementSyntaxNode> Statement;
        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    class DoWhileStatementSyntaxNode : public LoopStmt
    {
    public:
        RefPtr<StatementSyntaxNode> Statement;
        RefPtr<ExpressionSyntaxNode> Predicate;
        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    // The case of child statements that do control flow relative
    // to their parent statement.
    class JumpStmt : public ChildStmt
    {
    public:
        StatementSyntaxNode* parentStmt = nullptr;
    };

    class BreakStatementSyntaxNode : public JumpStmt
    {
    public:
        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    class ContinueStatementSyntaxNode : public JumpStmt
    {
    public:
        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    class ReturnStatementSyntaxNode : public StatementSyntaxNode
    {
    public:
        RefPtr<ExpressionSyntaxNode> Expression;
        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    class ExpressionStatementSyntaxNode : public StatementSyntaxNode
    {
    public:
        RefPtr<ExpressionSyntaxNode> Expression;
        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    // Note(tfoley): Moved this further down in the file because it depends on
    // `ExpressionSyntaxNode` and a forward reference just isn't good enough
    // for `RefPtr`.
    //
    class GenericAppExpr : public AppExprBase
    {
    public:
        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    // An expression representing re-use of the syntax for a type in more
    // than once conceptually-distinct declaration
    class SharedTypeExpr : public ExpressionSyntaxNode
    {
    public:
        // The underlying type expression that we want to share
        TypeExp base;

        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };


    // A modifier that indicates a built-in base type (e.g., `float`)
    class BuiltinTypeModifier : public Modifier
    {
    public:
        BaseType tag;
    };

    // A modifier that indicates a built-in type that isn't a base type (e.g., `vector`)
    //
    // TODO(tfoley): This deserves a better name than "magic"
    class MagicTypeModifier : public Modifier
    {
    public:
        String name;
        uint32_t tag;
    };

    // Modifiers that affect the storage layout for matrices
    class MatrixLayoutModifier : public Modifier {};

    // Modifiers that specify row- and column-major layout, respectively
    class RowMajorLayoutModifier : public MatrixLayoutModifier {};
    class ColumnMajorLayoutModifier : public MatrixLayoutModifier {};

    // The HLSL flavor of those modifiers
    class HLSLRowMajorLayoutModifier : public RowMajorLayoutModifier {};
    class HLSLColumnMajorLayoutModifier : public ColumnMajorLayoutModifier {};

    // The GLSL flavor of those modifiers
    //
    // Note(tfoley): The GLSL versions of these modifiers are "backwards"
    // in the sense that when a GLSL programmer requests row-major layout,
    // we actually interpret that as requesting column-major. This makes
    // sense because we interpret matrix conventions backwards from how
    // GLSL specifies them.
    class GLSLRowMajorLayoutModifier : public ColumnMajorLayoutModifier {};
    class GLSLColumnMajorLayoutModifier : public RowMajorLayoutModifier {};

    // More HLSL Keyword

    // HLSL `nointerpolation` modifier
    class HLSLNoInterpolationModifier : public Modifier {};

    // HLSL `linear` modifier
    class HLSLLinearModifier : public Modifier {};

    // HLSL `sample` modifier
    class HLSLSampleModifier : public Modifier {};

    // HLSL `centroid` modifier
    class HLSLCentroidModifier : public Modifier {};

    // HLSL `precise` modifier
    class HLSLPreciseModifier : public Modifier {};

    // HLSL `shared` modifier (which is used by the effect system,
    // and shouldn't be confused with `groupshared`)
    class HLSLEffectSharedModifier : public Modifier {};

    // HLSL `groupshared` modifier
    class HLSLGroupSharedModifier : public Modifier {};

    // HLSL `static` modifier (probably doesn't need to be
    // treated as HLSL-specific)
    class HLSLStaticModifier : public Modifier {};

    // HLSL `uniform` modifier (distinct meaning from GLSL
    // use of the keyword)
    class HLSLUniformModifier : public Modifier {};

    // HLSL `volatile` modifier (ignored)
    class HLSLVolatileModifier : public Modifier {};

    // An HLSL `[name(arg0, ...)]` style attribute.
    class HLSLAttribute : public Modifier
    {
    public:
        Token nameToken;
        List<RefPtr<ExpressionSyntaxNode>> args;
    };
        
    // An HLSL `[name(...)]` attribute that hasn't undergone
    // any semantic analysis.
    // After analysis, this might be transformed into a more specific case.
    class HLSLUncheckedAttribute : public HLSLAttribute
    {
    public:
    };

    // An HLSL `[numthreads(x,y,z)]` attribute
    class HLSLNumThreadsAttribute : public HLSLAttribute
    {
    public:
        // The number of threads to use along each axis
        int32_t x;
        int32_t y;
        int32_t z;
    };

    // HLSL modifiers for geometry shader input topology
    class HLSLGeometryShaderInputPrimitiveTypeModifier : public Modifier {};
    class HLSLPointModifier         : public HLSLGeometryShaderInputPrimitiveTypeModifier {};
    class HLSLLineModifier          : public HLSLGeometryShaderInputPrimitiveTypeModifier {};
    class HLSLTriangleModifier      : public HLSLGeometryShaderInputPrimitiveTypeModifier {};
    class HLSLLineAdjModifier       : public HLSLGeometryShaderInputPrimitiveTypeModifier {};
    class HLSLTriangleAdjModifier   : public HLSLGeometryShaderInputPrimitiveTypeModifier {};

    //

    // A generic declaration, parameterized on types/values
    class GenericDecl : public ContainerDecl
    {
    public:
        // The decl that is genericized...
        RefPtr<Decl> inner;

        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    inline Decl* GetInner(DeclRef<GenericDecl> const& declRef)
    {
        // TODO: Should really return a `DeclRef<Decl>` for the inner
        // declaration, and not just a raw pointer
        return declRef.getDecl()->inner.Ptr();
    }

    // The "type" of an expression that names a generic declaration.
    class GenericDeclRefType : public ExpressionType
    {
    public:
        GenericDeclRefType(DeclRef<GenericDecl> declRef)
            : declRef(declRef)
        {}

        DeclRef<GenericDecl> declRef;
        DeclRef<GenericDecl> const& GetDeclRef() const { return declRef; }

        virtual String ToString() override;

    protected:
        virtual bool EqualsImpl(ExpressionType * type) override;
        virtual int GetHashCode() override;
        virtual ExpressionType* CreateCanonicalType() override;
    };



    class GenericTypeParamDecl : public SimpleTypeDecl
    {
    public:
        // The bound for the type parameter represents a trait that any
        // type used as this parameter must conform to
//            TypeExp bound;

        // The "initializer" for the parameter represents a default value
        TypeExp initType;

        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    // A constraint placed as part of a generic declaration
    class GenericTypeConstraintDecl : public Decl
    {
    public:
        // A type constraint like `T : U` is constraining `T` to be "below" `U`
        // on a lattice of types. This may not be a subtyping relationship
        // per se, but it makes sense to use that terminology here, so we
        // think of these fields as the sub-type and sup-ertype, respectively.
        TypeExp sub;
        TypeExp sup;

        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    inline RefPtr<ExpressionType> GetSub(DeclRef<GenericTypeConstraintDecl> const& declRef)
    {
        return declRef.Substitute(declRef.getDecl()->sub);
    }

    inline RefPtr<ExpressionType> GetSup(DeclRef<GenericTypeConstraintDecl> const& declRef)
    {
        return declRef.Substitute(declRef.getDecl()->sup);
    }

    class GenericValueParamDecl : public VarDeclBase
    {
    public:
        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    // The logical "value" of a rererence to a generic value parameter
    class GenericParamIntVal : public IntVal
    {
    public:
        DeclRef<VarDeclBase> declRef;

        GenericParamIntVal(DeclRef<VarDeclBase> declRef)
            : declRef(declRef)
        {}

        virtual bool EqualsVal(Val* val) override;
        virtual String ToString() override;
        virtual int GetHashCode() override;
        virtual RefPtr<Val> SubstituteImpl(Substitutions* subst, int* ioDiff) override;
    };

    // Declaration of a user-defined modifier
    class ModifierDecl : public Decl
    {
    public:
        // The name of the C++ class to instantiate
        // (this is a reference to a class in the compiler source code,
        // and not the user's source code)
        Token classNameToken;

        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    // An empty declaration (which might still have modifiers attached).
    //
    // An empty declaration is uncommon in HLSL, but
    // in GLSL it is often used at the global scope
    // to declare metadata that logically belongs
    // to the entry point, e.g.:
    //
    //     layout(local_size_x = 16) in;
    //
    class EmptyDecl : public Decl
    {
    public:
        virtual RefPtr<SyntaxNode> Accept(SyntaxVisitor * visitor) override;
    };

    //

    class SyntaxVisitor
    {
    protected:
        DiagnosticSink * sink = nullptr;
        DiagnosticSink* getSink() { return sink; }

        SourceLanguage sourceLanguage = SourceLanguage::Unknown;
    public:
        void setSourceLanguage(SourceLanguage language)
        {
            sourceLanguage = language;
        }

        SyntaxVisitor(DiagnosticSink * sink)
            : sink(sink)
        {}
        virtual ~SyntaxVisitor()
        {
        }

        virtual RefPtr<ProgramSyntaxNode> VisitProgram(ProgramSyntaxNode* program)
        {
            for (auto & m : program->Members)
                m = m->Accept(this).As<Decl>();
            return program;
        }

        virtual void visitImportDecl(ImportDecl * decl) = 0;

        virtual RefPtr<FunctionSyntaxNode> VisitFunction(FunctionSyntaxNode* func)
        {
            func->ReturnType = func->ReturnType.Accept(this);
            for (auto & member : func->Members)
                member = member->Accept(this).As<Decl>();
            if (func->Body)
                func->Body = func->Body->Accept(this).As<BlockStatementSyntaxNode>();
            return func;
        }
        virtual RefPtr<ScopeDecl> VisitScopeDecl(ScopeDecl* decl)
        {
            // By default don't visit children, because they will always
            // be encountered in the ordinary flow of the corresponding statement.
            return decl;
        }
        virtual RefPtr<StructSyntaxNode> VisitStruct(StructSyntaxNode * s)
        {
            for (auto & f : s->Members)
                f = f->Accept(this).As<Decl>();
            return s;
        }
        virtual RefPtr<ClassSyntaxNode> VisitClass(ClassSyntaxNode * s)
        {
            for (auto & f : s->Members)
                f = f->Accept(this).As<Decl>();
            return s;
        }
        virtual RefPtr<GenericDecl> VisitGenericDecl(GenericDecl * decl)
        {
            for (auto & m : decl->Members)
                m = m->Accept(this).As<Decl>();
            decl->inner = decl->inner->Accept(this).As<Decl>();
            return decl;
        }
        virtual RefPtr<TypeDefDecl> VisitTypeDefDecl(TypeDefDecl* decl)
        {
            decl->Type = decl->Type.Accept(this);
            return decl;
        }
        virtual RefPtr<StatementSyntaxNode> VisitDiscardStatement(DiscardStatementSyntaxNode * stmt)
        {
            return stmt;
        }
        virtual RefPtr<StructField> VisitStructField(StructField * f)
        {
            f->Type = f->Type.Accept(this);
            return f;
        }
        virtual RefPtr<StatementSyntaxNode> VisitBlockStatement(BlockStatementSyntaxNode* stmt)
        {
            for (auto & s : stmt->Statements)
                s = s->Accept(this).As<StatementSyntaxNode>();
            return stmt;
        }
        virtual RefPtr<StatementSyntaxNode> VisitBreakStatement(BreakStatementSyntaxNode* stmt)
        {
            return stmt;
        }
        virtual RefPtr<StatementSyntaxNode> VisitContinueStatement(ContinueStatementSyntaxNode* stmt)
        {
            return stmt;
        }

        virtual RefPtr<StatementSyntaxNode> VisitDoWhileStatement(DoWhileStatementSyntaxNode* stmt)
        {
            if (stmt->Predicate)
                stmt->Predicate = stmt->Predicate->Accept(this).As<ExpressionSyntaxNode>();
            if (stmt->Statement)
                stmt->Statement = stmt->Statement->Accept(this).As<StatementSyntaxNode>();
            return stmt;
        }
        virtual RefPtr<StatementSyntaxNode> VisitEmptyStatement(EmptyStatementSyntaxNode* stmt)
        {
            return stmt;
        }
        virtual RefPtr<StatementSyntaxNode> VisitForStatement(ForStatementSyntaxNode* stmt)
        {
            if (stmt->InitialStatement)
                stmt->InitialStatement = stmt->InitialStatement->Accept(this).As<StatementSyntaxNode>();
            if (stmt->PredicateExpression)
                stmt->PredicateExpression = stmt->PredicateExpression->Accept(this).As<ExpressionSyntaxNode>();
            if (stmt->SideEffectExpression)
                stmt->SideEffectExpression = stmt->SideEffectExpression->Accept(this).As<ExpressionSyntaxNode>();
            if (stmt->Statement)
                stmt->Statement = stmt->Statement->Accept(this).As<StatementSyntaxNode>();
            return stmt;
        }
        virtual RefPtr<StatementSyntaxNode> VisitIfStatement(IfStatementSyntaxNode* stmt)
        {
            if (stmt->Predicate)
                stmt->Predicate = stmt->Predicate->Accept(this).As<ExpressionSyntaxNode>();
            if (stmt->PositiveStatement)
                stmt->PositiveStatement = stmt->PositiveStatement->Accept(this).As<StatementSyntaxNode>();
            if (stmt->NegativeStatement)
                stmt->NegativeStatement = stmt->NegativeStatement->Accept(this).As<StatementSyntaxNode>();
            return stmt;
        }
        virtual RefPtr<SwitchStmt> VisitSwitchStmt(SwitchStmt* stmt)
        {
            if (stmt->condition)
                stmt->condition = stmt->condition->Accept(this).As<ExpressionSyntaxNode>();
            if (stmt->body)
                stmt->body = stmt->body->Accept(this).As<BlockStatementSyntaxNode>();
            return stmt;
        }
        virtual RefPtr<CaseStmt> VisitCaseStmt(CaseStmt* stmt)
        {
            if (stmt->expr)
                stmt->expr = stmt->expr->Accept(this).As<ExpressionSyntaxNode>();
            return stmt;
        }
        virtual RefPtr<DefaultStmt> VisitDefaultStmt(DefaultStmt* stmt)
        {
            return stmt;
        }
        virtual RefPtr<StatementSyntaxNode> VisitReturnStatement(ReturnStatementSyntaxNode* stmt)
        {
            if (stmt->Expression)
                stmt->Expression = stmt->Expression->Accept(this).As<ExpressionSyntaxNode>();
            return stmt;
        }
        virtual RefPtr<StatementSyntaxNode> VisitVarDeclrStatement(VarDeclrStatementSyntaxNode* stmt)
        {
            stmt->decl = stmt->decl->Accept(this).As<DeclBase>();
            return stmt;
        }
        virtual RefPtr<StatementSyntaxNode> VisitWhileStatement(WhileStatementSyntaxNode* stmt)
        {
            if (stmt->Predicate)
                stmt->Predicate = stmt->Predicate->Accept(this).As<ExpressionSyntaxNode>();
            if (stmt->Statement)
                stmt->Statement = stmt->Statement->Accept(this).As<StatementSyntaxNode>();
            return stmt;
        }
        virtual RefPtr<StatementSyntaxNode> VisitExpressionStatement(ExpressionStatementSyntaxNode* stmt)
        {
            if (stmt->Expression)
                stmt->Expression = stmt->Expression->Accept(this).As<ExpressionSyntaxNode>();
            return stmt;
        }

        virtual RefPtr<ExpressionSyntaxNode> VisitOperatorExpression(OperatorExpressionSyntaxNode* expr)
        {
            for (auto && child : expr->Arguments)
                child->Accept(this);
            return expr;
        }
        virtual RefPtr<ExpressionSyntaxNode> VisitConstantExpression(ConstantExpressionSyntaxNode* expr)
        {
            return expr;
        }
        virtual RefPtr<ExpressionSyntaxNode> VisitIndexExpression(IndexExpressionSyntaxNode* expr)
        {
            if (expr->BaseExpression)
                expr->BaseExpression = expr->BaseExpression->Accept(this).As<ExpressionSyntaxNode>();
            if (expr->IndexExpression)
                expr->IndexExpression = expr->IndexExpression->Accept(this).As<ExpressionSyntaxNode>();
            return expr;
        }
        virtual RefPtr<ExpressionSyntaxNode> VisitMemberExpression(MemberExpressionSyntaxNode * stmt)
        {
            if (stmt->BaseExpression)
                stmt->BaseExpression = stmt->BaseExpression->Accept(this).As<ExpressionSyntaxNode>();
            return stmt;
        }
        virtual RefPtr<ExpressionSyntaxNode> VisitSwizzleExpression(SwizzleExpr * expr)
        {
            if (expr->base)
                expr->base->Accept(this);
            return expr;
        }
        virtual RefPtr<ExpressionSyntaxNode> VisitInvokeExpression(InvokeExpressionSyntaxNode* stmt)
        {
            stmt->FunctionExpr->Accept(this);
            for (auto & arg : stmt->Arguments)
                arg = arg->Accept(this).As<ExpressionSyntaxNode>();
            return stmt;
        }
        virtual RefPtr<ExpressionSyntaxNode> VisitTypeCastExpression(TypeCastExpressionSyntaxNode * stmt)
        {
            if (stmt->Expression)
                stmt->Expression = stmt->Expression->Accept(this).As<ExpressionSyntaxNode>();
            return stmt->Expression;
        }
        virtual RefPtr<ExpressionSyntaxNode> VisitVarExpression(VarExpressionSyntaxNode* expr)
        {
            return expr;
        }

        virtual RefPtr<ParameterSyntaxNode> VisitParameter(ParameterSyntaxNode* param)
        {
            return param;
        }
        virtual RefPtr<ExpressionSyntaxNode> VisitGenericApp(GenericAppExpr* type)
        {
            return type;
        }

        virtual RefPtr<Variable> VisitDeclrVariable(Variable* dclr)
        {
            if (dclr->Expr)
                dclr->Expr = dclr->Expr->Accept(this).As<ExpressionSyntaxNode>();
            return dclr;
        }

        virtual TypeExp VisitTypeExp(TypeExp const& typeExp)
        {
            TypeExp result = typeExp;
            result.exp = typeExp.exp->Accept(this).As<ExpressionSyntaxNode>();
            if (auto typeType = result.exp->Type.type.As<TypeType>())
            {
                result.type = typeType->type;
            }
            return result;
        }

        virtual void VisitExtensionDecl(ExtensionDecl* /*decl*/)
        {}

        virtual void VisitConstructorDecl(ConstructorDecl* /*decl*/)
        {}

        virtual void visitSubscriptDecl(SubscriptDecl* decl) = 0;

        virtual void visitAccessorDecl(AccessorDecl* decl) = 0;

        virtual void visitInterfaceDecl(InterfaceDecl* /*decl*/) = 0;

        virtual void visitInheritanceDecl(InheritanceDecl* /*decl*/) = 0;

        virtual RefPtr<ExpressionSyntaxNode> VisitSharedTypeExpr(SharedTypeExpr* typeExpr)
        {
            return typeExpr;
        }

        virtual void VisitDeclGroup(DeclGroup* declGroup)
        {
            for (auto decl : declGroup->decls)
            {
                decl->Accept(this);
            }
        }

        virtual RefPtr<ExpressionSyntaxNode> visitInitializerListExpr(InitializerListExpr* expr) = 0;
    };

    // Note(tfoley): These logically belong to `ExpressionType`,
    // but order-of-declaration stuff makes that tricky
    //
    // TODO(tfoley): These should really belong to the compilation context!
    //
    void RegisterBuiltinDecl(
        RefPtr<Decl>                decl,
        RefPtr<BuiltinTypeModifier> modifier);
    void RegisterMagicDecl(
        RefPtr<Decl>                decl,
        RefPtr<MagicTypeModifier>   modifier);

    // Look up a magic declaration by its name
    RefPtr<Decl> findMagicDecl(
        String const& name);

    // Create an instance of a syntax class by name
    SyntaxNodeBase* createInstanceOfSyntaxClassByName(
        String const&   name);

} // namespace Slang

#endif