Ragel State Machine Compiler

Ragel compiles executable finite state machines from regular languages. Ragel targets C, C++ and ASM. Ragel state machines can not only recognize byte sequences as regular expression machines do, but can also execute code at arbitrary points in the recognition of a regular language. Code embedding is done using inline operators that do not disrupt the regular language syntax.

The core language consists of standard regular expression operators (such as union, concatenation and Kleene star) and action embedding operators. The user’s regular expressions are compiled to a deterministic state machine and the embedded actions are associated with the transitions of the machine. Understanding the formal relationship between regular expressions and deterministic finite automata is key to using Ragel effectively.

Ragel also provides operators that let you control any non-determinism that you create, construct scanners, and build state machines using a statechart model. It is also possible to influence the execution of a state machine from inside an embedded action by jumping or calling to other parts of the machine, or reprocessing input.

Ragel provides a very flexible interface to the host language that attempts to place minimal restrictions on how the generated code is integrated into the application. The generated code has no dependencies.

Ragel code looks like:

action dgt      { printf("DGT: %c\n", fc); }
action dec      { printf("DEC: .\n"); }
action exp      { printf("EXP: %c\n", fc); }
action exp_sign { printf("SGN: %c\n", fc); }
action number   { /*NUMBER*/ }

number = (
    [0-9]+ $dgt ( '.' @dec [0-9]+ $dgt )?
    ( [eE] ( [+\-] $exp_sign )? [0-9]+ $exp )?
) %number;

main := ( number '\n' )*;

.. and it compiles to:

    if ( ++p == pe )
        goto out0;
    if ( 48 <= (*p) && (*p) <= 57 )
        goto tr0;
    goto st_err;
    { printf("DGT: %c\n", (*p)); }
    if ( ++p == pe )
        goto out1;
    switch ( (*p) ) {
        case 10: goto tr5;
        case 46: goto tr7;
        case 69: goto st4;
        case 101: goto st4;
    if ( 48 <= (*p) && (*p) <= 57 )
        goto tr0;
    goto st_err;

… and it visualizes as:


What kind of task is Ragel good for?




March 24, 2017
ragel-6.10.tar.gz (sig) (key)


Feb 15, 2021
(note that building ragel 7 requires colm)

Discussion and GIT Repos


To ask questions about using Ragel, or to discuss development, please use github discussions.

The original ragel mailing list is not longer running. Managing spam and staying off blacklists became too much of a nuisance. For older messages, checkout the mailing list archives.

GIT Repos

git clone ssh://git@github.com/adrian-thurston/ragel.git

git clone https://github.com/adrian-thurston/ragel.git


Beginning with the next development release (> Ragel is licensed under an MIT style license. Ragel 6 remains under GPL v2. Please see the file COPYING in the source.

Note: Part of the Ragel output is copied from Ragel source, covered by the MIT (or GPL v2) license. As an exception, you may use the parts of Ragel output copied from Ragel source without restriction. The remainder of Ragel output is derived from the input and inherits the copyright and license of the input file. Use of Ragel makes absolutely no requirement about the license of generated code.