[Git][ghc/ghc][wip/T23051] Wibble

[Simon Peyton Jones (@simonpj)]

Simon Peyton Jones pushed to branch wip/T23051 at Glasgow Haskell Compiler / GHC


Commits:
c2817f5a by Simon Peyton Jones at 2023-03-15T22:15:51+00:00
Wibble

- - - - -


1 changed file:

- compiler/GHC/Tc/Utils/TcMType.hs


Changes:

=====================================
compiler/GHC/Tc/Utils/TcMType.hs
=====================================
@@ -1444,13 +1444,16 @@ collect_cand_qtvs orig_ty is_dep cur_lvl bound dvs ty
                     -- See Note [Use level numbers for quantification]
 
       | case tcTyVarDetails tv of
-          SkolemTv {} -> True  -- lvl > pushTcLevel cur_lvl
-          _           -> False
+          SkolemTv _ lvl _ -> lvl > pushTcLevel cur_lvl
+          _                -> False
       = return dv  -- Skip inner skolems
         -- This only happens for erroneous program with bad telescopes
         -- e.g. BadTelescope2:  forall a k (b :: k). SameKind a b
         --      We have (a::k), and at the outer we don't want to quantify
         --      over the already-quantified skolem k.
+        -- (Apparently we /do/ want to quantify over skolems whose level sk_lvl is
+        -- sk_lvl > cur_lvl, but we definitely do; you get lots of failures otherwise.
+        -- A battle for another day.)
 
       | tv `elemDVarSet` kvs
       = return dv  -- We have met this tyvar already



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/c2817f5a630dfb10a5352c40a2da3beef218eddd

-- 
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/c2817f5a630dfb10a5352c40a2da3beef218eddd
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