On 08 February 2005 12:33, Thomas Jäger wrote:
First of all
-- Cale Gibbard comparing :: (Ord a) => (b -> a) -> b -> b -> Ordering comparing p x y = compare (p x) (p y) fits nicely with the ...By functions from Data.List.
sortBy (comparing fst) is just too cute not to have. Any objections?
readM :: (Monad m, Read a) => String -> m a readM s = case [x | (x,t) <- reads s, ("","") <- lex t] of [x] -> return x [] -> fail "Prelude.readM: no parse" _ -> fail "Prelude.readM: ambiguous parse"
Since there's no easy way to catch failure of read operations, this function seems to be quite natural.
Also subsumes System.IO.readIO. Looks useful to me.
Finally,
-- Koen Claessen selections :: [a] -> [(a,[a])] selections [] = [] selections (x:xs) = (x,xs) : [ (y,x:ys) | (y,ys) <- selections xs ]
permutations :: [a] -> [[a]] permutations [] = [[]] permutations xs = [ y : zs | (y,ys) <- selections xs , zs <- permutations ys ] are quite useful (maybe they should be named select and permute since most Data.List names seem to be imperatives).
Both look reasonable. Not all the names in Data.List are imperative (eg. inits, tails, lines, words). I think the names are fine. Cheers, Simon