defaultGamma = extend "print" (Forall ["a"] ((IdType "a") ->> VoidType))
$ extend "isEmpty" (Forall ["a"] ((ListType (IdType "a")) ->> BoolType))
$ extend "read" (Forall [] (FuncType CharType))
+ $ extend "1printchar" (Forall [] (CharType ->> VoidType))
+ $ extend "1printint" (Forall [] (IntType ->> VoidType))
+ $ extend "1printbool" (Forall [] (BoolType ->> VoidType))
zero
sem :: AST -> Either [SemError] AST