Re: [Haskell-beginners] Re: multreplace

I think your first attempt using list comprehension is nearly ok but is in fact a fold: multRepl str ss rs = foldl (uncurry . replace) str (zip ss rs) or something similar. On Thu, 2010-07-01 at 23:58 -0700, prad wrote:

On Thu, 1 Jul 2010 22:31:28 -0700 prad wrote:

...

so back to the drawing board!

here's what emerged:

====== #!/usr/bin/env runghc

module Main where

import Useful as U

main = do

let str = "This is original string" let ss = ["orig","ing"] let rs = ["very orig","ucture"]

putStrLn $ head (multRepl str ss rs)

--multRepl :: String -> [String] -> [String] -> [String] multRepl [] _ _ = [] multRepl str (s:ss) (r:rs) = do let newStr = U.replace str s r if (length ss) == 0 then return newStr else multRepl newStr ss rs =======

this does produce the correct output: This is very original structure

and here are my questions:

1. the type *Main Useful> :t multRepl multRepl :: (Eq t) => [t] -> [[t]] -> [[t]] -> [[t]]

but i have it returning newStr which equals U.replace str s r and the type of U.replace is String as shown below *Main Useful> :t Useful.replace Useful.replace :: (Eq a) => [a] -> [a] -> [a] -> [a]

so why is it returning [String] when newStr isn't a list of strings?

2. is the way i've done it proper haskellian? it took me quite some time to think this out trying to find my way through the fog of imperative programming.

(my apologies for replying to my own posts - as well as my appreciation for your assistance)