[GHC] #13302: Let in do-notation with braces does not parse

19 Feb 2017

      #13302: Let in do-notation with braces does not parse
-------------------------------------+-------------------------------------
           Reporter:  rem            |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.2
           Keywords:  do-notation,   |  Operating System:  MacOS X
  let, parse                         |
       Architecture:                 |   Type of failure:  GHC rejects
  Unknown/Multiple                   |  valid program
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 According to the the syntax at
 https://www.haskell.org/onlinereport/haskell2010/haskellch10.html the
 following do-notation should parse:

 {{{#!hs
 do {let x = 4; print x}
 }}}

 But it doesn't.

 {{{#!hs
 do {let x = 4 in print x}
 }}}

 parses OK. Doesn't look like a new bug, I tried with GHC 7.8 and same
 result. Googling "haskell do {let ds; es} =  let ds in do {es}" also shows
 quite a lot of people taught Haskell that way, so maybe it once worked?

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13302
GHC http://www.haskell.org/ghc/
The Glasgow Haskell Compiler