[GHC] #12376: Allow function definitions in record syntax

[GHC]

#12376: Allow function definitions in record syntax
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        Reporter:  Iceland_jack      |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by nomeata):

 Replying to [comment:3 Iceland_jack]:
 > A hypothetical `\case2` may be better
 >
 > {{{#!hs
 > eqList a = MkEq
 >   { (==) = \case2
 >       ([],   [])   -> True
 >       (x:xs, y:ys) -> ...
 >       (_,    _)    -> False
 >   , (/=) = neqDef (eqList a)
 >   }
 > }}}
 >
 > Given an extension that allows user to omit tuple parentheses when un-
 ambiguous (similar to Agda's `_,_` constructor which looks like `a , b`
 when applied to two arguments) this looks even better
 >
 > {{{#!hs
 > eqList a = MkEq
 >   { (==) = \case2
 >       [],   []   -> True
 >       x:xs, y:ys -> ...
 >       _,    _    -> False
 >   , (/=) = neqDef (eqList a)
 >   }
 > }}}

 Why not go all the way and allow the full syntax of function definitions
 here, just as in a module scope, in an instance declaration, in a where
 clause or in a let clause:

 {{{#!hs
 eqList a = MkEq
   { []     ==        = True
     (x:xs) == (y:ys) = …
      _     == _      = False
   , (/=) = neqDef (eqList a)
   }
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12376#comment:5>
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