Poor parse error

Given the fragment:

f x = do case x of
            Just foo -> do
                stmt1
                stmt2
                stmt3
                stmt4
                stmt5
                stmt6
            Nothing -> 
                a <- var
                stmt1
                stmt2
                stmt3

There is a parse error after the Nothing, I should have included a do.

GHC says:

bug.hs:1:9: Parse error in pattern

This error message can be made to be arbitrarily far away from the point at which the error actually occurs.

Haskell-src-exts does far better with:

bug.hs:10:19: Parse error in pattern

Reporting <- binding errors against the arrow, rather than the (assumed) start of the pattern seems to be a better choice.

Trac metadata

Trac field	Value
Version	6.10.4
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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