[plt-scheme] Typed scheme: Cannot apply expression of type Procedure, since it is not a function type

> 
> You might want polymorphism here, or variable arity polymorphism, but
> I'd have to be sure of what you were trying to do.


I'm just looking for a way to represent functions - so I have this 'Fun' type storing the function's name, return type and arguments (up till now I have a number type and a string type only, represented by symbols N and S), and the action it's supposed to execute, which would be the scheme function if an appropriate one exists or a lambda expression otherwise.
Then I really just want to extract the code from this representation and apply it to some given object... just like in the made-up example I posted.

And this should work for every kind of function, so yes it should be variable arity, but also variable return types - just some general possibility to apply "anything at all" to anything - like if I had

(define-struct: Fun ((name : Symbol) (proc : Procedure) (args : (Listof Symbol)) (ret : Symbol))) 

(define f1 (make-Fun 'plus + '(N N) 'N)) 
((Fun-proc f1) 1 2) 


(define f2 (make-Fun 'substr substring '(S  N N) 'S)) 
((Fun-proc f2) "astring" 2 4) 


and it worked...
I don't know if this sounds silly, but I wouldn't know how I could represent functions in another way.

Ciao,
Sigrid

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