[Haskell-cafe] Text.Regex.matchRegex: Success is empty?

[Kiss Csongor]

Hi Jeffrey,

It returns ‘Just’, because the pattern was found.

The list is empty, because no capture groups are defined in the regex.

matchRegex (mkRegex “(a)”)  “abracadabra"
returns Just [“a”]

Csongor

> On 5 Apr 2016, at 22:16, Jeffrey Brown <jeffbrown.the at gmail.com> wrote:
> 
> Esteemed Haskellers,
> 
> It is working for me, but I am puzzled by the matchRegex function:
> 
>     > import Text.Regex
>     > :i matchRegex
>     matchRegex :: Regex -> String -> Maybe [String]
>             -- Defined in ‘Text.Regex’
> 
> Searches that fail return Nothing:
> 
>     > matchRegex (mkRegex "z") "abracadabra"
>     Nothing
> 
> which makes sense. But why do searches that succeed return an empty list of Strings?
> 
>     > matchRegex (mkRegex "a") "abracadabra"
>     Just []
>     > 
> 
> -- 
> Jeffrey Benjamin Brown
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