Re: [Haskell-beginners] wrapping text in a multiline string

Thank you for this important detail. Following the advice in this thread I tried to rewrite the function in terms of the lower-level interface instead of using =~~ -- qualified import to avoid clashes in main program import qualified Text.Regex.PCRE as RE regexReplace' :: String -> (String -> String) -> String -> String regexReplace' regex replace text = go text where regex' :: RE.Regex regex' = RE.makeRegexOpts RE.defaultCompOpt RE.defaultExecOpt regex replace' :: RE.MatchText String -> String replace' = undefined go text = case RE.matchOnceText regex' text of Just (before, match, after) -> before ++ replace' match ++ go after _ -> text Did you mean something like this? (besides that the replace' function still has to be filled in) If this is correct ... I am still a little lost though. I cannot come up with a way of matching the actual String out of the MatchText returned by matchOnceText ... http://hackage.haskell.org/packages/archive/regex-base/latest/doc/html/Text-... If I should structure the entire function differently, I would be very grateful to receive some pointers how. Best regards, rico On Wed, Jun 6, 2012 at 7:50 PM, Chaddaï Fouché wrote:

On Wed, Jun 6, 2012 at 10:39 AM, Rico Moorman wrote:

...

Now I am wondering how I would integrate this in the replacement function or how to rewrite it properly.

Looking at the type signature of =~~ (with my limited knowledge) it seems that I would have to "use" RegexMaker adding up the CompOptions needed?

(=~~) :: (RegexMaker Regex CompOption ExecOption source, RegexContext Regex source1 target, Monad m) => source1 -> source -> m target

What's non-obvious and trip a lot of people when they try to use regexes in Haskell is that most regex libraries use the same interface, which is specified in the regex-base and consists of several typeclasses that offers a very high degree of flexibility. =~and =~~ are only the simplified front-ends to this and are pretty inadequate for advanced usages (for instance compile and use multiple time the same regex, you should really avoid =~ in this case, or additional regex compilation options). To see the basic interface, look at Text.Regex.Base.RegexLike : http://hackage.haskell.org/packages/archive/regex-base/latest/doc/html/Text-... . In particular, what you want to do should be done with makeRegexOpts and match (or matchM), note that the available compilation and execution options can vary depending on the regex library you use and for regex-pcre, they're documented there : http://hackage.haskell.org/packages/archive/regex-pcre/latest/doc/html/Text-...

-- Jedaï