diff options
| -rw-r--r-- | compiler/typecheck/TcHsType.hs | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/compiler/typecheck/TcHsType.hs b/compiler/typecheck/TcHsType.hs index 274fd3998d..5635b2d7b7 100644 --- a/compiler/typecheck/TcHsType.hs +++ b/compiler/typecheck/TcHsType.hs @@ -1787,7 +1787,7 @@ Note [Promotion in signatures] If an unsolved metavariable in a signature is not generalized (because we're not generalizing the construct -- e.g., pattern sig -- or because the metavars are constrained -- see kindGeneralizeSome) -we need to promote to maintain (MetaTvInv) of Note [TcLevel and untouchable type variables] +we need to promote to maintain (WantedTvInv) of Note [TcLevel and untouchable type variables] in TcType. Note that promotion is identical in effect to generalizing and the reinstantiating with a fresh metavariable at the current level. So in some sense, we generalize *all* variables, but then re-instantiate @@ -1804,7 +1804,7 @@ than the surrounding context.) This kappa cannot be solved for while checking the pattern signature (which is not kind-generalized). When we are checking the *body* of foo, though, we need to unify the type of x with the argument type of bar. At this point, the ambient TcLevel is 1, and spotting a -matavariable with level 2 would violate the (MetaTvInv) invariant of +matavariable with level 2 would violate the (WantedTvInv) invariant of Note [TcLevel and untouchable type variables]. So, instead of kind-generalizing, we promote the metavariable to level 1. This is all done in kindGeneralizeNone. |