I would be inclined to add type annotations as an extra constructor of
the expression representation type.
data Exp
= IntExp Integer
| VarExp Symbol
| AssignExp Symbol Exp
| IfExp Exp Exp (Maybe Exp)
| CallExp Symbol [Exp]
| LetExp [Dec] Exp
| Exp `HasType` Ty
This is particularly useful if the source language allows arbitrary
type annotations on expressions, because it can cover both the user-
supplied annotations, and the compiler-inferred ones. Also, your type
inference phase is free to add as many or as few annotations into the
AST as it wishes - they are not required everywhere.
Regards,
Malcolm
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