Hi, you can make every function being an instance of class Show, this works for me: instance Show (a -> b) where show _ = "FUNCTION" data Element = Int Int | Float Float | Func (Machine -> Machine) deriving Show David Johan Grönqvist wrote:
I am a haskell-beginner and I wish to write a Forth-like interpreter. (Only for practice, no usefulness.)
I would like use a list (as stack) that can contain several kinds of values.
data Element = Int Int | Float Float | Func : Machine -> Machine | ...
Now I would like to have this type be an instance of the class Show, so that I can see what the stack contains in ghci.
"deriving Show" is impossible as Func is not instance of Show. Can I make it instance of Show? I just want to define something like
show (Func _) = "Function, cannot show"
and I am not interested in actually displaying any information about the function, but I am interested in getting information about elements of other kinds.
So far I have just guessed, but failed to produce anything that does not give an error stating that my function is not of the form (T a b c) where T is not an alias and a b c are simple type variables (or so).
Any help appreciated!
Johan
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