print (FunExpr _ id as fs) = printFunCall id as fs
print (EmptyListExpr _) = ["[]"]
print (TupleExpr _ (e1, e2)) = ["(":print e1] ++ [",":print e2] ++ [")"]
+ print (LambdaExpr _ args e) = ["\\":args] ++ ["->": print e]
instance toString Expr where
toString e = concat $ print e