[Haskell-cafe] How does one use Text.Regex.Base.RegexLike?

[Daniel Fischer]

Am Dienstag, 23. Dezember 2008 21:09 schrieb Lyle Kopnicky:
> Yes, sort of. It enables me to get some simple examples working with (=~).
> But I still don't know how to get makeRegex to work. You need it to specify
> options like case insensitivity, or to use functions like matchAllText.
>

Your problem is that GHC can't know which instance to choose. You can help it 
by giving a type signature, e.g.

rx :: Regex
rx = makeRegex "a(.*)A"

HTH,
Daniel

> > At Tue, 23 Dec 2008 11:21:41 -0800,
> >
> > Lyle Kopnicky wrote:
> > > I'm trying to migrate code from using the old Text.Regex to the new
> > > Text.Regex.Base. But, I'm getting type errors. I can't even create a
> >
> > regex.
> >
> > > Looking at the docs, it seems like this should print "bcd":
> > >
> > > import Data.Array
> > > import Text.Regex.Base
> > > import Text.Regex.Posix
> > >
> > > rx = makeRegex "a(.*)A"
> > >
> > > Just (_, mt, _) = matchOnceText rx "abcdA"
> > >
> > > main = putStrLn (fst (mt ! 0))
> > >
> > >
> > > But I get an error:
> > >
> > > src\regex.hs:5:5:
> > >     No instance for (RegexMaker regex compOpt execOpt [Char])
> > >       arising from a use of `makeRegex' at src\regex.hs:5:5-22
> > >     Possible fix:
> > >       add an instance declaration for
> > >       (RegexMaker regex compOpt execOpt [Char])
> > >     In the expression: makeRegex "a(.*)A"
> > >     In the definition of `rx': rx = makeRegex "a(.*)A"
> > >
> > > src\regex.hs:7:18:
> > >     No instance for (RegexLike regex [Char])
> > >       arising from a use of `matchOnceText' at src\regex.hs:7:18-41
> > >     Possible fix:
> > >       add an instance declaration for (RegexLike regex [Char])
> > >     In the expression: matchOnceText rx "abcdA"
> > >     In a pattern binding: Just (_, mt, _) = matchOnceText rx "abcdA"
> > >
> > > Why does it say there is no instance? Isn't the instance imported by
> > > Text.Regex.Posix?
> > >
> > > Why in the world is it so complicated just to get a matched substring
> > > out
> >
> > of
> >
> > > the text? Is there an easier way?
> > >
> > > Thanks,
> > > Lyle
> > > [1.2  <text/html; ISO-8859-1 (7bit)>]
> > >
> > > [2  <text/plain; us-ascii (7bit)>]
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