#1189: Add First and Last wrappers around Maybe to Data.Monoid
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Reporter: jyasskin | Owner:
Type: proposal | Status: new
Priority: normal | Milestone: Not GHC
Component: libraries/base | Version: 6.6
Severity: normal | Resolution:
Keywords: | Difficulty: Unknown
Testcase: | Architecture: Unknown
Os: Unknown |
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Comment (by jyasskin):
Ross Paterson suggested that the "obvious" instance directly on Maybe was
to combine two Just's using a Monoid instance on their contents and set
mempty==Nothing. David House, Stefan O'Rear, and Jan-Willem Maessen agreed
so I added it.
John Meacham objected to the location of all of the types currently in
Data.Monoid, but that's a broader discussion than this patch, and nobody
expressed agreement anyway.
David Menendez and Spencer Janssen suggested that Maybe's Monoid instance
should match its MonadPlus instance, but neither provided an argument
supporting that.
The thread is archived at http://www.haskell.org/pipermail/libraries/2007-
March/006950.html
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1189>
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