[Haskell-cafe] Folding function composition: L or R?

[Henning Thielemann]

On Wed, 7 Jul 2004, Graham Klyne wrote:

> [[
> sss :: [ShowS]
> sss = map (++) ["abc","def","ghi","jkl"]
> 
> ssr = foldr (.) id sss
> ssl = foldl (.) id sss
> 
> sr = ssr ""
> sl = ssl ""
> 
> -- sl == sr == "abcdefghijkl"
> -- is there any efficiency difference?
> ]]
> 
> Conventional wisdom suggests that foldr is better, but I'm not sure if it 
> really matters in this case.

foldl performs worse, e.g. for infinite lists it will need infinite
time :-)