Commit a262ea49 authored by Simon Peyton Jones's avatar Simon Peyton Jones

Significant refactor of Lint

This refactoring of Lint was triggered by #17923, which is
fixed by this patch.

The main change is this.  Instead of
   lintType :: Type -> LintM LintedKind
we now have
   lintType :: Type -> LintM LintedType

Previously, all of typeKind was effectively duplicate in lintType.
Moreover, since we have an ambient substitution, we still had to
apply the substition here and there, sometimes more than once. It
was all very tricky, in the end, and made my head hurt.

Now, lintType returns a fully linted type, with all substitutions
performed on it.  This is much simpler.

The same thing is needed for Coercions.  Instead of
  lintCoercion :: OutCoercion
               -> LintM (LintedKind, LintedKind,
                         LintedType, LintedType, Role)
we now have
  lintCoercion :: Coercion -> LintM LintedCoercion

Much simpler!  The code is shorter and less bug-prone.

There are a lot of knock on effects.  But life is now better.
parent 6d172e63
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