types

type Array struct {
	Elem Type
}

type Bool struct {
}

type Env struct {
	// Types for declarations. This is referred by type variables to resolve
	// type variables' actual types
	//
	// XXX:
	// Currently nested identifiers don't work. Example:
	//   let
	//     x = 42
	//   in
	//     let x = true in print_bool (x);
	//     print_int (x)
	// We need alpha transform before type inference in order to ensure
	// all symbol names are unique.
	DeclTable map[string]Type
	// External variable names which are referred but not defined.
	// External variables are exposed as external symbols in other object files.
	Externals map[string]*External
	// GoCaml uses let-polymorphic type inference. It means that instantiation occurs when new
	// symbol is introduced. So instantiation only occurs at variable reference.
	RefInsts map[string]*Instantiation
	// Mappings from generic type to instantiated types for each declarations.
	// e.g.
	//   'a -> 'a => {int -> int, bool -> bool, float -> float}
	//
	// Note: This is set in sema/deref.go
	PolyTypes map[Type][]*Instantiation
}

type External struct {
	Type  Type
	CName string
}

type Float struct {
}

type Fun struct {
	Ret    Type
	Params []Type
}

type Instantiation struct {
	// From is a generic type variable instantiated.
	From Type
	// To is a type variable instantiated from generic type variable.
	To Type
	// Mapping from ID of generic type variable to actual instantiated type variable
	Mapping []*VarMapping
}

type Int struct {
}

type Option struct {
	Elem Type
}

type String struct {
}

type Tuple struct {
	Elems []Type
}

type Type interface {
	String() string
}

type Unit struct {
}

type Var struct {
	Ref   Type
	Level int
	ID    VarID
}

type VarID uint64

type VarMapping struct {
	ID   VarID
	Type Type
}

type Visitor interface {
	// VisitTopdown defines the process when a type is visited. This method is called before
	// children are visited.
	// Returned value is a next visitor to use for succeeding visit. When wanting to stop
	// visiting, please return nil.
	// A visitor visits in depth-first order.
	VisitTopdown(t Type) Visitor
	// VisitBottomup defines the process when a type is visited. This method is called after
	// children were visited. When VisitTopdown returned nil, this method won't be caled for the type.
	VisitBottomup(t Type)
}