Good afternoon,

Pursuing my goal of making a lisp syntax for Ocaml, I began to take a
close look at the AST (Ocaml-3.09.3/parsing/parsetree.mli). I don't
understand some of the constructors in the type expression_desc:


| Pexp_function of label * expression option * (pattern * expression) list
What is the "expression option" for?

| Pexp_construct of Longident.t * expression option * bool

What is the boolean for?

| Pexp_variant of label * expression option

What is a "variant"? (Does not seem to be related to variant types, as
"Pexp_construct" is used for them)

| Pexp_record of (Longident.t * expression) list * expression option
What is the "expression option" for?

| Pexp_constraint of expression * core_type option * core_type option
Why two "core_type option", instead of just a "core_type"?

| Pexp_when of expression * expression
Why not "pattern * expression"?

| Pexp_send of expression * string
What does "Pexp_send" stand for?

| Pexp_new of Longident.t
What does "Pexp_new" stand for?

| Pexp_setinstvar of string * expression
What does "Pexp_setinstvar" stand for?

| Pexp_override of (string * expression) list
What does "Pexp_override" stand for?

| Pexp_lazy of expression
Why does this constructor even exist? Are some specific optimizations made?

| Pexp_poly of expression * core_type option
What does "Pexp_poly" stand for?


Phew, I am done, for now. Except one question: is the AST likely to
change, or else is it likely to be standardized (so any freak like me
can try her fancy syntax)?.

By the way, I would like to see documentation about the AST (or other
related part of Ocaml's implementation). The sources are great, and
highly readable, but I am afraid of hitting a wall.

Thanks
Loup