[GHC] #1222: Add the "optionMaybe" combinator to Parsec

[GHC]

#1222: Add the "optionMaybe" combinator to Parsec
-------------------------------------------------+--------------------------
    Reporter:  Maxime Henrion <mux at FreeBSD.org>  |       Owner:         
        Type:  proposal                          |      Status:  new    
    Priority:  normal                            |   Milestone:         
   Component:  libraries (other)                 |     Version:  6.6    
    Severity:  minor                             |    Keywords:         
  Difficulty:  Easy (1 hr)                       |    Testcase:         
Architecture:  Unknown                           |          Os:  Unknown
-------------------------------------------------+--------------------------
This patch adds a new combinator named 'optionMaybe' that is just a
 specialized version of the existing 'option' combinator: it wraps the
 result into a Maybe type with the expected semantics.  That is,
 intuitively, if the parser fails, 'Nothing' is returned, and if the parser
 succeeds, 'Just a' is returned (with 'a' being the type of the parser).

 It seems generally useful, and has received positive feedback from the
 haskell-cafe mailing list and on the #haskell IRC channel, where several
 people have already written something similar a few times.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1222>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler