#5236: Circular functional dependencies cause loop in typechecker
---------------------------------+------------------------------------------
Reporter: dimitris | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler (Type checker)
Version: 7.0.3 | Keywords:
Testcase: | Blockedby:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: None/Unknown
---------------------------------+------------------------------------------
In the attached file, a dictionary (Id A B) is rewritten with two
functional dependencies (A -> B, B -> A) and two errors are added in our
constraint bag (rightfully so), but the new workitem is symmetric (Id B
A), goes back in the worklist and in the new iteration of the solver we
have exactly the same process repeated.
This is a solveInteractWithDepth loop, not a solve_wanteds loop.
I think the right thing to do is in doTopReact: (1) first try to apply
functional dependencies, (2) then check if an instance matches, and (3) do
a ContinueWith or a Stop but never throw the workitem back in the worklist
as happens now. I have to discuss
this with Simon.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5236>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
_______________________________________________
Glasgow-haskell-bugs mailing list
[email protected]
http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
