At 14:24 07/07/04 +0200, Henning Thielemann wrote:

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 :-)

Of course! And your answer makes me notice an important touchstone when dealing with such questions: "what happens with an infinite list?". Thanks! #g ------------ Graham Klyne For email: http://www.ninebynine.org/#Contact