[GHC] #9042: List indenting in case fails

[GHC]

#9042: List indenting in case fails
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        Reporter:  laar              |            Owner:
            Type:  bug               |           Status:  closed
        Priority:  normal            |        Milestone:
       Component:  Compiler          |          Version:  7.8.2
      Resolution:  invalid           |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Changes (by goldfire):

 * status:  new => closed
 * resolution:   => invalid


Comment:

 I would say GHC's behavior in this case is correct. According to (my
 understanding of) the layout rule, the first character after a layout
 herald (the `of`, in your case) sets the new indentation level (provided
 it is not too far left!). So, your open-bracket sets the indentation
 level. Then, your comma is at the same level of indentation, so GHC
 inserts a `;` before the comma, causing the parse error.

 So, that syntax ''is'' available in patterns, as witness by the following
 (accepted) code:

 {{{
 t = case Just [1..2] of
         Just [ 1
              , 2
              ] -> True
         _ -> False
 }}}

 In this example, the `J` of the `Just` in the pattern sets the indentation
 level, so there's no problem laying out the list vertically.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9042#comment:1>
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