|
|
For instance, consider this inductive type:
Inductive Ind := A | B | C | D.
For detecting "match" on this type, one was forced earlier to write code
in Ltac using "match goal" and/or "context [...]" and long patterns such as:
match _ with A => _ | B => _ | C => _ | D => _ end
After this patch, this pattern can be shortened in many alternative ways:
match _ with A => _ | _ => _ end
match _ with B => _ | _ => _ end
match _ in Ind with _ => _ end
Indeed, if we want to detect a "match" of a given type, we can either
leave at least one branch where a constructor is explicit, or use a "in"
annotation.
Now, we can also detect any "match" regardless of its type:
match _ with _ => _ end
Note : this will even detect "match" over empty inductive types.
Compatibility should be preserved, since "match _ with end" will
continue to correspond only to empty inductive types.
Internally, the constr_pattern PCase has changed quite a lot, a few elements
are now grouped into a case_info_pattern record, while branches are now
lists of given sub-patterns.
NB: writing "match" with missing last branches in a constr pattern was actually
tolerated by Pattern.pattern_of_glob_constr earlier, since the number of
constructor per inductive is unknown there. And this was triggering an uncaught
exception in a array_fold_left_2 in Matching later. Oups. At least this patch
fixes this issue...
Btw: the code in Pattern.pattern_of_glob_constr was quadratic in the number
of branch in a match pattern. I doubt this was really a problem, but having now
linear code instead cannot harm ;-)
git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@14644 85f007b7-540e-0410-9357-904b9bb8a0f7
|
letouzey