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| author | Richard Eisenberg <richard.eisenberg@tweag.io> | 2022-05-13 15:15:10 -0400 |
|---|---|---|
| committer | Richard Eisenberg <rae@richarde.dev> | 2022-05-26 02:42:57 +0000 |
| commit | f2814d14b32f7fd732691cd1c1f682692ca8c0fc (patch) | |
| tree | 5de06187b03c4507ea2a2be8a3dea1e85e82aa6f /compiler/GHC/Tc/Solver/InertSet.hs | |
| parent | 5678f017a69dc758d0edabbdaad755bd5efef465 (diff) | |
| download | haskell-wip/T21515.tar.gz | |
Generalize breakTyVarCycle to work with TyFamLHSwip/T21515
The function breakTyVarCycle_maybe has been installed
in a dark corner of GHC to catch some gremlins (a.k.a.
occurs-check failures) who lurk
there. But it previously only caught gremlins of the
form (a ~ ... F a ...), where some of our intrepid users
have spawned gremlins of the form (G a ~ ... F (G a) ...).
This commit improves breakTyVarCycle_maybe (and renames
it to breakTyEqCycle_maybe) to catch the new gremlins.
Happily, the change is remarkably small.
The gory details are in Note [Type equality cycles].
Test cases: typecheck/should_compile/{T21515,T21473}.
Diffstat (limited to 'compiler/GHC/Tc/Solver/InertSet.hs')
| -rw-r--r-- | compiler/GHC/Tc/Solver/InertSet.hs | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/compiler/GHC/Tc/Solver/InertSet.hs b/compiler/GHC/Tc/Solver/InertSet.hs index f7d0eb0701..4de3ca8d1f 100644 --- a/compiler/GHC/Tc/Solver/InertSet.hs +++ b/compiler/GHC/Tc/Solver/InertSet.hs @@ -240,7 +240,7 @@ type CycleBreakerVarStack = NonEmpty [(TcTyVar, TcType)] -- first element in the stack corresponds to current implication; -- later elements correspond to outer implications -- used to undo the cycle-breaking needed to handle - -- Note [Type variable cycles] in GHC.Tc.Solver.Canonical + -- Note [Type equality cycles] in GHC.Tc.Solver.Canonical -- Why store the outer implications? For the use in mightEqualLater (only) data InertSet @@ -1693,7 +1693,7 @@ This is best understood by example. where cbv = F a The cbv is a cycle-breaker var which stands for F a. See - Note [Type variable cycles] in GHC.Tc.Solver.Canonical. + Note [Type equality cycles] in GHC.Tc.Solver.Canonical. This is just like case 6, and we say "no". Saying "no" here is essential in getting the parser to type-check, with its use of DisambECP. |