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

[Adam Bergmark]

The regex-compat docs say "

Returns: 

https://hackage.haskell.org/packages/archive/base/4.5.0.0/doc/html/Data-Maybe.html#v:Just

 strs

 if the match succeeded (and 

strs

 is the list of subexpression matches), or 

https://hackage.haskell.org/packages/archive/base/4.5.0.0/doc/html/Data-Maybe.html#v:Nothing

 otherwise.

”

.

Adam Bergmark

On Tue 05 Apr 2016 at 22:16 Jeffrey Brown

<
mailto: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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