#984: Syntax error shows in the wrong position
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Reporter: guest | Owner:
Type: bug | Status: new
Priority: low | Milestone: _|_
Component: Compiler (Parser) | Version: 6.4.2
Severity: minor | Resolution:
Keywords: syntax parse case do | Difficulty: Unknown
Testcase: | Architecture: Multiple
Os: Multiple |
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Changes (by simonmar):
* architecture: x86 => Multiple
* milestone: => _|_
* severity: normal => minor
* priority: normal => low
* os: Linux => Multiple
Comment:
In a sense, GHC is telling you something completely sensible here, but it
wasn't what you were expecting. Let me add some parentheses to your code:
{{{
f _ = do
x <- computation
(case () of
_ ->
result) <- computation
case () of () -> undefined
}}}
See now? You've written a binding statement (`pattern <- expr`), where
the pattern is in fact a case expression, so GHC complains that the case
expression is not a valid pattern. Indeed, if you use `-ferror-spans`,
you'll see that the span of the error covers the parenthesised case
expression.
It might be difficult for us to do anything better here. We kind-of want
the case expression to eliminate the possibility of a binding statement
from the parser, but there's no easy way to do that in GHC's parser.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/984>
GHC <http://www.haskell.org/ghc/>
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