CODEWITHSUNDEEP
regexhaskell
Alexey Orlov
Alexey Orlov

Reputation: 2814

Haskell, Regex: reduce a string to a list of matches

How am I supposed, say, to create a list of matches:

> "aa2gg3tt41u" =~ "\\d+" :: [String]

produces an error no matter how I fool with the type annotation. I expect something like ["2","3","41"].

Upvotes: 0

Views: 363

Answers (1)

Zeta
Zeta

Reputation: 105915

You want to use instance RegexLike a b => RegexContext a b [[b]]:

> "aa2gg3tt41u" =~ "[0-9]+" :: [[String]]
[["2"],["3"],["41"]]

I hear you say, "why the [[String]]?" Well, keep in mind that regexes support grouping:

> "aa2gg3tt41u" =~ "([a-z]+)[0-9]" :: [[String]]
[["aa2","aa"],["gg3","gg"],["tt4","tt"]]

The first element in a list will always be the complete match, followed by the sub-matches. If you're just interested in the complete match, use map head or provide your own operator:

(?=~) :: String -> String -> [String]
str ?=~ re = map head (str =~ re)

Upvotes: 2

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