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  • #9415

Closed
Open
Opened Aug 06, 2014 by Richard Eisenberg@raeDeveloper

Superclass cycle with ambiguous type causes loop

If I say

class D a => C a where
  meth :: D a => ()
class C a => D a

I get a loop in the typechecker.

I know what's going on here: the error for the superclass cycle is added during the validity check, but then we go on to do ambiguity checks. Unfortunately, the ambiguity check never finishes. We just need to bail when there are superclass errors before doing the ambiguity check.

Patch on the way.

Trac metadata
Trac field Value
Version 7.9
Type Bug
TypeOfFailure OtherFailure
Priority normal
Resolution Unresolved
Component Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture
Assignee
Assign to
7.8.4
Milestone
7.8.4 (Past due)
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None
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Reference: ghc/ghc#9415