Loup Vaillant wrote:
> 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:

Reading the source for the parser (where these constructors are used) 
and comparing it with the documentation should help you find the answers 
to almost all of your questions.

Parser source:
http://camlcvs.inria.fr/cgi-bin/cvsweb/ocaml/parsing/parser.mly?rev=1.126

Language reference:
http://caml.inria.fr/pub/docs/manual-ocaml/manual008.html

Jeremy.