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  • Simon Peyton Jones's avatar
    [project @ 2003-12-17 11:29:40 by simonpj] · ca0b7c66
    Simon Peyton Jones authored
      Fix a subtle loop in the context-reduction machinery
    This bug was provoked by a recent change: when trying to prove
    a constraint C, TcSimplify.reduce now adds C to the database before
    trying to prove C, thus building recursive dictionaries.
    Two bugs
    a) If we add C's superclasses (which we were) we can now build a
       bogusly-recursive dictionary (see Note [SUPERCLASS-LOOP]).
       Solution: in reduce, add C only (via addIrred NoSCs) and then
       later use addWanted to add its definition plus SCs.
    b) Since we can have recursive definitions, the superclass-loop
       handling machinery (findAllDeps) must carry its visited-set
       with it (which it was not doing before)
    The main file is TcSimplify; but I modified a bunch of others to
    take advantage of new function extendVarSetList