[wg-camlp4] Changes to the Parsetree

[Alain Frisch]

Dear all,

Here is a list of the most important recent changes I've applied to the 
Parsetree in the extension_points branch.  The primary goals are to 
reduce the number of implicit invariants (not represented in the data 
structure itself) and make the Parsetree more user-friendly.

  - Splitting Pexp_constraint into two constructors, one to represent 
type constraints (e : t), another one to represent type coercion (e : t1 
:> t2) or (e :> t).

  - Splitting Pexp_function into two constructors, one for "function P1 
-> E1 | ... | Pn -> En", another for "fun P -> E / fun ~l:P -> E / fun 
?l:P -> E / fun ?l:(P = E) -> E".  (And removing support for "fun P when 
E -> E".)

  - Merging Pexp_assertfalse into Pexp_assert.

  - Keeping an explicit representation of interval patterns.

  - Explicit representation of "when" guards for function/match/try in a 
new "case" record type {pc_lhs: pattern; pc_guard: expression option; 
pc_rhs: expression}, instead of Pexp_when.

  - And a few more, listed in extension_points.txt.


Don't hesitate to comment on those changes, or to suggest other ones.

Also, the Parsetree module now documents all constructions and tries to 
list required invariants.


Alain