[GHC] #10751: Implement Phase 1 of MonadFail Proposal (MFP)

[GHC]

#10751: Implement Phase 1 of MonadFail Proposal (MFP)
-------------------------------------+-------------------------------------
        Reporter:  hvr               |                   Owner:  quchen
            Type:  task              |                  Status:  patch
        Priority:  highest           |               Milestone:  8.0.1
       Component:  Compiler          |                 Version:  7.10.2
      Resolution:                    |                Keywords:  report-
                                     |  impact
Operating System:  Unknown/Multiple  |            Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:  Phab:D1248
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Comment (by ekmett):

 My sense is that support within the committee or this proposal is very
 high, based on various discussions.

 I will however, take a moment to formally poll for objections within the
 committee just to make absolutely sure before I commit to signing off.

 That said, would it be possible to move the proposal from a github page to
 the Haskell Wiki for posterity?

 That would make it easier to express questions about minor points, e.g.
 whether `ViewPatterns`/`PatternSynonyms` should always be considered
 failable or if they should only be considered failable if their right hand
 side is.

 e.g.

 {{{
 pattern Foo = ((),())
 }}}

 is clearly an unfailable pattern.

 as is

 {{{
 foo (snd -> x) = ...
 }}}

 as 'x' is unfailable.

 These compose for useful patterns like

 {{{
 pattern Polar x y <- (magnitude &&& phase -> (x,y)) where
   Polar x y = mkPolar x y
 }}}

 Those items there are probably the primary sticking point I have
 personally, but in broad strokes I personally absolutely adore this
 proposal.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10751#comment:12>
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