Commits on Sep 20, 2021

1. [minor] switch.ml: distinguish types for arguments, tests and actions …

   Before this change, Switch will use 'make_if' either with tests
   explicitly constructed from the provided primitives, or with
   a matching scrutinee/argument directly to check that it is
   non-zero. (Arguments are expected to be implicitly coercible to
   booleans for the 'make_if' functions.)
   
   This assumption may not always hold, for example if we tried to define
   a switch construct on tagged integers in
   asmcomp/cmm_helpers.ml. (I have a followup commit doing just that.)
   The comparison primitives of Cmm return untagged booleans, the
   conditional test is untagged, but a tagged integer cannot be tested
   for non-zeroness by just using untagged 'if' directly.
   
   The present commit clarifies the matter by separating the type of
   actions, tests and arguments at the Switch level. It does not change
   behavior in any way, but it makes it much easier to follow these
   distinctions. (In particular, it the new typing discipline
   demonstrates that the dangerous use of 'make_if' only happens exactly
   once in the Switch functor.)

   

   gasche committed Sep 20, 2021
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