Function composition and currying

[Dr Mark H Phillips]

Thanks to all the people who responded to my question!

The solution from Wolfgang Jeltsch:

  (f.).g

was what I was after.  But the other responses were
useful also.

Thanks!

Mark.

On Thu, 2003-07-17 at 09:57, Dr Mark H Phillips wrote:
> Hi,
> 
> Hopefully this is a simple question.  I am wanting to know good ways
> of using ".", the function composition operator, when dealing with
> currying functions.
> 
> Suppose I have the following functions defined:
> 
>   f :: Int -> Int
>   f x = x*x
> 
>   g :: Int -> Int -> Int
>   g a b = a + b
> 
> If I wish to add 1 and 2 together and then square them I can do:
> 
>   f (g 1 2) = 9
> 
> but what if I wish to use function composition in the process?
> 
> I can't do 
> 
>   (f.g) 1 2
> 
> because the 2 doesn't get passed in till too late.
> 
> I could do
> 
>   (f.(g 1)) 2
> 
> or even
> 
>   (f.(uncurry g)) (1,2)
> 
> But what I really want is a function with signature Int -> Int -> Int.
> The answer is probably:
> 
>   (curry (f.(uncurry g))) 1 2
> 
> but this seems awfully messy just to do f (g 1 2).
> 
> And what if g were a function with three curried arguments?  Then
> uncurry and curry wouldn't apply.  What then?
> 
> Is there a better way?
> 
> Thanks,
> 
> Mark.
> 
> 
> -- 
> Dr Mark H Phillips
> Research Analyst (Mathematician)
> 
> AUSTRICS - smarter scheduling solutions - www.austrics.com
> 
> Level 2, 50 Pirie Street, Adelaide SA 5000, Australia
> Phone +61 8 8226 9850
> Fax   +61 8 8231 4821
> Email mark@austrics.com.au
> 
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-- 
Dr Mark H Phillips
Research Analyst (Mathematician)

AUSTRICS - smarter scheduling solutions - www.austrics.com

Level 2, 50 Pirie Street, Adelaide SA 5000, Australia
Phone +61 8 8226 9850
Fax   +61 8 8231 4821
Email mark@austrics.com.au