// val-defs.h

// Syntax class definitions for compile-time values.

// A compile-time integer (may not have a specific concrete value)
ABSTRACT_SYNTAX_CLASS(IntVal, Val)
END_SYNTAX_CLASS()

// Trivial case of a value that is just a constant integer
SYNTAX_CLASS(ConstantIntVal, IntVal)
    FIELD(IntegerLiteralValue, value)

    RAW(
    ConstantIntVal()
    {}
    ConstantIntVal(IntegerLiteralValue value)
        : value(value)
    {}

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

// The logical "value" of a rererence to a generic value parameter
SYNTAX_CLASS(GenericParamIntVal, IntVal)
    DECL_FIELD(DeclRef<VarDeclBase>, declRef)

    RAW(
    GenericParamIntVal()
    {}
    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;
)
END_SYNTAX_CLASS()

// A witness to the fact that some proposition is true, encoded
// at the level of the type system.
//
// Given a generic like:
//
//     void example<L>(L light)
//          where L : ILight
//     { ... }
//
// a call to `example()` needs two things for us to be sure
// it is valid:
//
// 1. We need a type `X` to use as the argument for the
//    parameter `L`. We might supply this explicitly, or
//    via inference.
//
// 2. We need a *proof* that whatever `X` we chose conforms
//    to the `ILight` interface.
//
// The easiest way to make such a proof is by construction,
// and a `Witness` represents such a constructive proof.
// Conceptually a proposition like `X : ILight` can be
// seen as a type, and witness prooving that proposition
// is a value of that type.
//
// We construct and store witnesses explicitly during
// semantic checking because they can help us with
// generating downstream code. By following the structure
// of a witness (the structure of a proof) we can, e.g.,
// navigate from the knowledge that `X : ILight` to
// the concrete declarations that provide the implementation
// of `ILight` for `X`.
// 
ABSTRACT_SYNTAX_CLASS(Witness, Val)
END_SYNTAX_CLASS()

// A witness that one type is a subtype of another
// (where by "subtype" we include both inheritance
// relationships and type-conforms-to-interface relationships)
//
// TODO: we may need to tease those apart.
ABSTRACT_SYNTAX_CLASS(SubtypeWitness, Witness)
    FIELD(RefPtr<Type>, sub)
    FIELD(RefPtr<Type>, sup)
END_SYNTAX_CLASS()

// A witness that one type is a subtype of another
// because some in-scope declaration says so
SYNTAX_CLASS(DeclaredSubtypeWitness, SubtypeWitness)
    FIELD(DeclRef<Decl>, declRef);
RAW(
    virtual bool EqualsVal(Val* val) override;
    virtual String ToString() override;
    virtual int GetHashCode() override;
)
END_SYNTAX_CLASS()

// A value that is used as a proxy when we need to
// put an IR-level value into AST types
SYNTAX_CLASS(IRProxyVal, Val)
    FIELD(IRValue*, inst)
RAW(
    virtual bool EqualsVal(Val* val) override;
    virtual String ToString() override;
    virtual int GetHashCode() override;
)
END_SYNTAX_CLASS()