Re: [Haskell-cafe] Re: [Haskell] Trying to get a Composite design pattern to work

Chris Kuklewicz wrote:

Neil Mitchell wrote:

...

...

How's this? What about ++, in Haskell thats just an ordinary function, yet you are using the library one in this case.

(++) a b = foldr (:) b a

or

(++) = flip (foldr (:))

so

concat = foldr (flip (foldr (:))) []

also

map = (\f -> foldr ((:).f) [])

thus

concatMap = (\f -> (foldr (flip (foldr (:))) []) . (foldr ((:).f) []))

No recursive definitions in sight...all built with foldr

Of course, I should only need one [] in the optimal definition: concatMap = (\f -> (foldr (flip (foldr (:)).f) [])) Which lambdabot can make "pointless" by eliminating the \f-> concatMap = flip foldr [] . (flip (foldr (:)) .) -- Chris