Parsing grammars using OCaml

Question

I have a task to write a (toy) parser for a (toy) grammar using OCaml and not sure how to start (and proceed with) this problem.

Here\'s a sample Awk grammar:

<

Answer 1

I'm not sure if you specifically require the derivation tree, or if this is a just a first step in parsing. I'm assuming the latter.

You could start by defining the structure of the resulting abstract syntax tree by defining types. It could be something like this:

type expr =
    | Operation of term * binop * term
    | Term of term
and term =
    | Num of num
    | Lvalue of expr
    | Incrop of incrop * expression
and incrop = Incr | Decr
and binop = Plus | Minus
and num = int

Then I'd implement a recursive descent parser. Of course it would be much nicer if you could use streams combined with the preprocessor camlp4of...

By the way, there's a small example about arithmetic expressions in the OCaml documentation here.