Re: [Haskell-cafe] Re: Function composition

Adapting my previous class sample with these ideas, we have: class Multicompose t1 t2 t3 | t1 t2 -> t3 where infixr 9 +. (+.)::t1 -> t2 -> t3 instance Multicompose t1 t2 t3 => Multicompose t1 (a -> t2) (a -> t3) where (+.) = (.).(+.) instance Multicompose (b -> c) (a -> b) (a -> c) where (+.) = (.) The only advantage is having the compiler calculate the number of compositions. Cheers, Jorge. Stuart Cook escreveu:

On 10/4/07, Dominic Steinitz wrote:

...

Look at the type of (.).(.).(.)

Indeed, this generalizes to functions of any arity on the "RHS":

Prelude> :t (.) (.) :: (b -> c) -> (a -> b) -> a -> c

Prelude> :t (.).(.) (.).(.) :: (b -> c) -> (a -> a1 -> b) -> a -> a1 -> c

Prelude> :t (.).(.).(.) (.).(.).(.) :: (b -> c) -> (a -> a1 -> a2 -> b) -> a -> a1 -> a2 -> c

Prelude> :t (.).(.).(.).(.) (.).(.).(.).(.) :: (b -> c) -> (a -> a1 -> a2 -> a3 -> b) -> a -> a1 -> a2 -> a3 -> c

Of course, if you want higher-arity functions anywhere *other* than the head of your composition chain, you'll have to resort to tupling and uncurrying.

Stuart _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

Jorge M. Pelizzoni ICMC - Universidade de São Paulo