• Simon Peyton Jones's avatar
    Fix a bad error in tcMatchTy · 1e2e82aa
    Simon Peyton Jones authored
    This patch fixes #17395, a very subtle and hard-to-trigger
    bug in tcMatchTy.  It's all explained in
      Note [Matching in the presence of casts (2)]
    I have not added a regression test because it is very hard
    to trigger it, until we have the upcoming mkAppTyM patch,
    after which lacking this patch means you can't even compile
    the libraries.
Unify.hs 60.9 KB