[GHC] #7071: Refactoring arrows

[GHC]

#7071: Refactoring arrows
---------------------------------+------------------------------------------
    Reporter:  simonpj           |       Owner:                  
        Type:  bug               |      Status:  new             
    Priority:  normal            |   Milestone:                  
   Component:  Compiler          |     Version:  7.4.2           
    Keywords:                    |          Os:  Unknown/Multiple
Architecture:  Unknown/Multiple  |     Failure:  None/Unknown    
  Difficulty:  Unknown           |    Testcase:                  
   Blockedby:                    |    Blocking:                  
     Related:                    |  
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Comment(by simonpj):

 Daniel asks what kind of `Stmts` can occur in arrow commands.  Here's a
 table that expresses what can occur where.
 {{{
            -------- HsStmtContext -----------------
            Pattern       List  PArr
 Stmt       guards   GHCi comp  comp   do  mdo  arrow
 -------------------------------------------------------
 LastStmt                   x     x     x   x    ??
 BindStmt    x        x     x     x     x   x    x
 ExprStmt    x        x     x     x     x   x    x
 LetStmt     x        x     x     x     x   x    x
 ParStmt                    x
 TransStmt                  x
 RecStmt                                x   x    x
 }}}
 Once we are sure it's right, it'd be good to add it to `HsExpr`.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7071#comment:4>
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