[Chicken-hackers] [PATCH 5] Fix compiler-typecase trail restore

[megane]

Hi,

Here's a small fix.

Consider this example:

(compiler-typecase (list 2 'a)
  ((forall (x) (list x x)) 1)
  (else #t))

Trying to compile this causes an error in the compiler:

Error: (cdr) bad argument type: #f

In this typecase the first case fails (cannot match/unify 2 and 'a). The
failed match however leaves type variable 'x' in the trail.

The call (trail-restore trail0 typeenv) tries to restore the trail. But
it uses the typeenv from '(list 2 'a)', which doesn't contain the type
variable 'x'. It should instead use the typeenv used in the match-types
call, the combination of typeenvs for '(forall (x) (list x x))' and
'(list 2 'a)'.


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