Genlex(3) OCaml library Genlex(3)

# [NAME](#NAME)

Genlex - A generic lexical analyzer.

# [Module](#Module)

Module Genlex

# [Documentation](#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 instance, **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 notation 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 -&gt; char Stream.t -&gt; 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 **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.

2026-09-15 OCamldoc

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Document: Genlex(3o) from ocaml-4 4.14.4-r3 (Chainguard OS)
Source: https://github.com/ocaml/ocaml