Genlex(3o) OCaml library Genlex(3o)
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 OCaml, 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 in-
stance, int , and would have rules such as:
let rec parse_expr = parser
| [< n1 = parse_atom; n2 = parse_remainder n1 >] -> n2
and parse_atom = parser
| [< 'Int n >] -> n
| [< 'Kwd "("; n = parse_expr; 'Kwd ")" >] -> n
and parse_remainder n1 = parser
| [< 'Kwd "+"; n2 = parse_expr >] -> n1 + n2
| [< >] -> n1
One should notice that the use of the parser keyword and associated no-
tation for streams are only available through camlp4 extensions. This
means that one has to preprocess its sources e. g. by using the "-pp"
command-line switch of the compilers.
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 key-
words. 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
Stream.Error with the offending lexeme as its parameter) otherwise.
Blanks and newlines are skipped. Comments delimited by (* and *) are
skipped as well, and can be nested. A Stream.Failure exception is
raised if end of stream is unexpectedly reached.
OCamldoc 2023-02-12 Genlex(3o)
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