Genlex(3)

NAME
Genlex - A generic lexical analyzer.

Module
Module Genlex

Documentation

Module Genlex
 : sig end

A generic lexical analyzer.

This module implements a simple ``standard'' lexical analyzer, presented as a function from character streams to token streams. It implements roughly the lexical conventions of Caml, but is parameterized by the set of keywords of your language.

Example: a lexer suitable for a desk calculator is obtained by let lexer = make_lexer ["+";"-";"*";"/";"let";"="; ( ; ) ]

The associated parser would be a function from token stream to, for instance, int , and would have rules such as:

let parse_expr = parser [< 'Int n >] -> n | [< 'Kwd ( ; n = parse_expr; 'Kwd ) >] -> n | [< n1 = parse_expr; n2 = parse_remainder n1 >] -> n2 and parse_remainder n1 = parser [< 'Kwd + ; n2 = parse_expr >] -> n1+n2 | ...

type token =
 | Kwd of string
 | Ident of string
 | Int of int
 | Float of float
 | String of string
 | Char of char

The type of tokens. The lexical classes are: Int and Float for integer and floating-point numbers; String for string literals, enclosed in double quotes; Char for character literals, enclosed in single quotes; Ident for identifiers (either sequences of letters, digits, underscores and quotes, or sequences of ``operator characters'' such as + , * , etc); and Kwd for keywords (either identifiers or single ``special characters'' such as ( , } , etc).

val make_lexer : string list -> char Stream.t -> token Stream.t

Construct the lexer function. The first argument is the list of keywords. An identifier s is returned as Kwd s if s belongs to this list, and as Ident s otherwise. A special character s is returned as Kwd s if s belongs to this list, and cause a lexical error (exception Parse_error ) otherwise. Blanks and newlines are skipped. Comments delimited by (* and *) are skipped as well, and can be nested.