[GHC] #12178: Allow inline pragmas on pattern synonyms

[GHC]

#12178: Allow inline pragmas on pattern synonyms
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        Reporter:  mpickering        |                Owner:  (none)
            Type:  feature request   |               Status:  new
        Priority:  high              |            Milestone:  8.8.1
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
                                     |  PatternSynonyms, newcomer
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 simonpj):

 > Why would a pattern synonym not get inlined by default, always?

 The only disadvantage to inlining is code size; and that applies equally
 to all inlining decisions, whether for pattern synonyms or any other
 function.  Consider
 {{{
 pattern P a = [[[[a]]]]
 f x = P (x+1)
 g y = P (y-1)
 }}}
 Here's what it compiles to, without inlining
 {{{
 $bP x = (:) ((:) ((:) ((:) x []) []) []) []
 f x = $bP (x+1)
 g y = $bP (y-1)
 }}}
 Yes, we could inline `$bP`:
 {{{
 f x = (:) ((:) ((:) ((:) (x+1) []) []) []) []
 g y = (:) ((:) ((:) ((:) (y-1) []) []) []) []
 }}}
 But really nothing much was gained by inlining the builder `$bp`.

 It's the same for matching.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12178#comment:11>
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