Trying a hack to support {'pat|P} without breaking compatibility.

Concretely, we bypass the following limitation: The notation
"{ ' pat | P }" broke the parsing of expressions of the form
"{ forall x, P } + { Q }". Indeed the latter works thanks to a
tolerance of Camlp5 in parsing "forall x, P" at level 200 while the
rule asks to actually parse the interior of "{ ... }" at level 99 (the
reason for 99 is to be below the rule for "M : T" which is at level
100, so that "{ x : A | P }" does not see "x : A" as a cast). Adding
an extra "'"; pat = pattern in parallel to c = constr LEVEL "99" broke
the tolerance for constr at level 200.

We fix this by adding an ad hoc rule for "{ binder_constr }" in the
native grammar (g_constr.ml4).

Actually, this is inconsistent with having a rule for "{ constr at level 99 }"
in Notations.v. We should have both rules in Notations.v or both rules
hard-wired in the native grammar. But I still don't know what is the best
decision to take, so leaving as it at the current time.

Advantages of hard-wiring both rules in g_constr.ml4: a bit simpler in
metasyntax.ml (no need to ensure that the rule exist). Disadvantages:
if one wants a different initial state without the business needing
the "{ }" for sumbool, sumor, sig, sigT, one still have the rules
there.

Advantages of having them in Notations.v: more modular, we can change
the initial state. Disadvantages: one would need a new kind of
modifier, something like "x at level 99 || binder_constr", with all
the difficulty to find a nice, intuitive, name for "binder_constr",
and the difficulty of understanding if there is a generality to this
"||" disjunction operator, and whether it should be documented or not.

1 files changed, 2 insertions, 0 deletions

diff --git a/parsing/g_constr.ml4 b/parsing/g_constr.ml4
index c2ce003f1..9f12db649 100644
--- a/parsing/g_constr.ml4
+++ b/parsing/g_constr.ml4
@@ -219,6 +219,8 @@ GEXTEND Gram
                 CAst.make ~loc:(!@loc) @@ CNotation("( _ )",([c],[],[],[]))
             | _ -> c)
       | "{|"; c = record_declaration; "|}" -> c
+      | "{"; c = binder_constr ; "}" ->
+          CAst.make ~loc:(!@loc) @@ CNotation(("{ _ }"),([c],[],[],[]))
       | "`{"; c = operconstr LEVEL "200"; "}" ->
 	  CAst.make ~loc:(!@loc) @@ CGeneralization (Implicit, None, c)
       | "`("; c = operconstr LEVEL "200"; ")" ->