[GHC] #8769: Minor refactoring of Maybe.lhs

[GHC]

#8769: Minor refactoring of Maybe.lhs
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        Reporter:  Iceland_jack       |            Owner:
            Type:  bug                |           Status:  patch
        Priority:  lowest             |        Milestone:
       Component:  libraries (other)  |          Version:  7.7
      Resolution:                     |         Keywords:
Operating System:  Unknown/Multiple   |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown       |       Difficulty:  Unknown
       Test Case:                     |       Blocked By:
        Blocking:                     |  Related Tickets:
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Comment (by Iceland_jack):

 I removed `mapCatMaybes`, `allMaybes` and `maybeToBool` completely from
 `Maybes`, I decided to keep `firstJust` since the name is clearer than
 `msum` (should `orElse` be moved to `Data.Maybe`? it seems to be the sole
 reason for importing `Maybes` much of the time).

 Did you have any other modules in mind that needed cleanup?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8769#comment:5>
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