[Haskell-cafe] function terms

[Ian Childs]

Yes they are Haskell expressions - I called them terms because  
actually they are GADTs of type Term a and Term b. I can't use type  
'b -> c' as they are part of a larger pattern.

I have a function that returns a witness to 's :: Term a' and 't ::  
Term b' having the same type, if they do, but I am wondering how to  
extend this to the first argument of an arrow type.

Thanks

On 6 Jul 2011, at 10:23, Henning Thielemann wrote:

>
> On Wed, 6 Jul 2011, Ian Childs wrote:
>
>> Suppose I have two terms s and t of type "a" and "b" respectively,  
>> and I want
>> to write a function that returns s applied to t if "a" is an arrow  
>> type of
>> form "b -> c", and nothing otherwise. How do i convince the  
>> compiler to
>> accept the functional application only in the correct instance?
>
> Why can't 's' simply have type 'b -> c'? With "term" do you mean a  
> Haskell
> expression?