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Confusing parser error in 8.6

    • Open Issue created by Iavor S. Diatchki @yav

    Consider the following example:

    f x =
  case x of
    A -> 'a'
   B -> 'b'

    The problem here is that B is misaligned, which is quite a common mistake, especially in a bigger case block.

    GHC reports the following error:

        Unexpected case expression in function application:
        case x of { A -> 'a' }
    You could write it with parentheses
    Or perhaps you meant to enable BlockArguments?

    This is quite confusing, especially since the program won't parse, BlockArguments or not. My guess is that we are being a bit too eager with reporting the BlockArguments issue.

    One way to work around this would be to just remember if we used BlockArguments while parsing, but only do the check that the extension is enabled after a successful parse.

    Trac metadata
    Trac field Value
    Version 8.6.1
    Type Bug
    TypeOfFailure OtherFailure
    Priority normal
    Resolution Unresolved
    Component Compiler (Parser)
    Test case
    Differential revisions
    BlockedBy
    Related
    Blocking
    CC
    Operating system
    Architecture
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