[Haskell-cafe] regular expression sub-expression matching

[Nicolas Bock]

Hi Roman and Bob,

thanks a lot for the help. I ended up using getAllTextSubmatches as
explained by Bob, since I had that package already installed on my system.
Works great!

Thanks,

nick



On Fri, Jan 18, 2013 at 5:52 PM, Bob Ippolito <bob at redivi.com> wrote:

> Note that Haskell doesn't convert "\(" to "\\(" like Python does, so the
> regex string has been changed. It's not so easy to figure out how to use
> this library from the documentation because of all the typeclass trickery.
>
> h> import Text.Regexp.Posix (getAllTextSubmatches, (=~))
> h> getAllTextSubmatches ("M(1,2) = 0.1e-3;" =~ "M\\(([0-9]+),([0-9]+)\\)
> *= *([0-9.eE-]+);") :: [String]
> ["M(1,2) = 0.1e-3;","1","2","0.1e-3"]
>
> If it doesn't match, you'll get an empty list. You can join the tail of
> the match list together with Data.List.intercalate, and print it out with
> putStrLn. The if null case would just return ().
>
> To demonstrate some of the typeclass trickery going on here, you could ask
> for the results as an Array with Int indexes of String.
>
> h> import Text.Regexp.Posix (getAllTextSubmatches, (=~))
> h> import Data.Array ((!), Array)
> h> let matches = getAllTextSubmatches ("M(1,2) = 0.1e-3;" =~
> "M\\(([0-9]+),([0-9]+)\\) *= *([0-9.eE-]+);") :: Array Int String
> h> matches
> array (0,3) [(0,"M(1,2) = 0.1e-3;"),(1,"1"),(2,"2"),(3,"0.1e-3")]
> h> map (matches !) [1..3]
> ["1","2","0.1e-3"]
>
> -bob
>
> On Fri, Jan 18, 2013 at 3:25 PM, Nicolas Bock <nicolasbock at gmail.com>wrote:
>
>> Hello list,
>>
>> I was wondering whether there is a way to do what the following python
>> code does in haskell:
>>
>> import re
>>
>> result = re.compile("M\(([0-9]+),([0-9]+)\) *=
>> *([0-9.eE-]+);").search("M(1,2) = 0.1e-3;")
>> if result:
>>   print(result.group(1), result.group(2), result.group(3))
>>
>> Basically I would like to pattern match parts of a string and return the
>> matches. I have looked at Text.Regex.Posix but (of course I might just not
>> have understood the functions in there properly) it seems as if it does not
>> provide anything like python's re module.
>>
>> Thanks already,
>>
>> nick
>>
>>
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>>
>>
>
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