package re

  1. Overview
  2. Docs
RE is a regular expression library for OCaml

Install 

dune-project
 Dependency

github.com Readme Changelog LGPL-2.1-or-later WITH OCaml-LGPL-linking-exception License Edit opam file Versions (20)

Authors

  1. J
    Jerome Vouillon
  2. T
    Thomas Gazagnaire
  3. A
    Anil Madhavapeddy
  4. R
    Rudi Grinberg
  5. Gabriel Radanne

Maintainers

  1. R
    Rudi Grinberg <me@rgrinberg.com>

Sources

1.14.0.tar.gz
md5=03f4a83100cb9229a796b85c698076e1
sha512=cd2cc39f951ca6b7be631bbb5531ed13bc040e629842671bf6fef3911b20ef1653fa9a1f0aa23b094d252cffc9a9efe7ffca69e50d362ab935bc0cc447548124

Description

Pure OCaml regular expressions with:

  • Perl-style regular expressions (module Re.Perl)
  • Posix extended regular expressions (module Re.Posix)
  • Emacs-style regular expressions (module Re.Emacs)
  • Shell-style file globbing (module Re.Glob)
  • Compatibility layer for OCaml's built-in Str module (module Re.Str)

Published: 22 Sep 2025

README

Description

Re is a regular expression library for OCaml. Build status

Contact

This library has been written by Jerome Vouillon (Jerome.Vouillon@pps.univ-paris-diderot.fr). It can be downloaded from https://github.com/ocaml/ocaml-re

Bug reports, suggestions and contributions are welcome.

Features

The following styles of regular expressions are supported:

  • Perl-style regular expressions (module Re.Perl);
  • Posix extended regular expressions (module Re.Posix);
  • Emacs-style regular expressions (module Re.Emacs);
  • Shell-style file globbing (module Re.Glob).

It is also possible to build regular expressions by combining simpler regular expressions (module Re).

The most notable missing features are back-references and look-ahead/look-behind assertions.

There is also a subset of the PCRE interface available in the Re.Pcre module. This makes it easier to port code from that library to Re with minimal changes.

Performances

The matches are performed by lazily building a DFA (deterministic finite automaton) from the regular expression. As a consequence, matching takes linear time in the length of the matched string.

The compilation of patterns is slower than with libraries using back-tracking, such as PCRE. But, once a large enough part of the DFA is built, matching is extremely fast.

Of course, for some combinations of regular expression and string, the part of the DFA that needs to be build is so large that this point is never reached, and matching will be slow. This is not expected to happen often in practice, and actually a lot of expressions that behaves badly with a backtracking implementation are very efficient with this implementation.

The library is at the moment entirely written in OCaml. As a consequence, regular expression matching is much slower when the library is compiled to bytecode than when it is compiled to native code.

Here are some timing results (Pentium III 500Mhz):

  • Scanning a 1Mb string containing only as, except for the last character which is a b, searching for the pattern aa?b (repeated 100 times):

    • RE: 2.6s
    • PCRE: 68s

  • Regular expression example from http://www.bagley.org/~doug/shootout/ [1]

    • RE: 0.43s
    • PCRE: 3.68s

    [1] this page is no longer up but is available via the Internet Archive http://web.archive.org/web/20010429190941/http://www.bagley.org/~doug/shootout/bench/regexmatch/

  • The large regular expression (about 2000 characters long) that Unison uses with my preference file to decide whether a file should be ignored or not. This expression is matched against a filename about 20000 times.

    • RE: 0.31s
    • PCRE: 3.7s However, RE is only faster than PCRE when there are more than about 300 filenames.

Dependencies (2)

  1. ocaml >= "4.13.0"
  2. dune >= "3.17"

Dev Dependencies (5)

  1. odoc with-doc
  2. conf-npm with-test
  3. js_of_ocaml with-test
  4. ounit2 with-test
  5. ppx_expect with-test

  1. alcotest
  2. alcotest-async
  3. alcotest-lwt
  4. alcotest-mirage
  5. atd >= "2.2.1"
  6. atdcpp
  7. atdd
  8. atdgen >= "2.3.3"
  9. atdgen-runtime = "2.2.1"
  10. atdj >= "2.2.1"
  11. atdpy >= "2.4.1"
  12. atds < "2.3.3"
  13. atdts
  14. aws-config
  15. awsm-codegen
  16. BetterErrors
  17. bap-byteweight-frontend
  18. bap-callgraph-collator
  19. bap-fsi-benchmark
  20. bap-ida
  21. bap-objdump
  22. bap-print >= "2.2.0"
  23. bap-radare2
  24. benchpress
  25. bibfmt
  26. bio_io >= "0.5.1"
  27. biocaml
  28. bistro < "0.6.0"
  29. bonsai >= "v0.15.0"
  30. caisar >= "4.0"
  31. calculon
  32. calculon-web
  33. caldav
  34. calendar >= "3.0.0"
  35. camlp5 >= "8.02.01"
  36. camlp5-buildscripts
  37. camyll
  38. caqti >= "1.7.0"
  39. catala
  40. chamo
  41. cinaps >= "v0.10.0"
  42. cohttp
  43. coin
  44. colibri2
  45. commons
  46. conan >= "0.0.6"
  47. core_bench
  48. core_extended
  49. cosovo
  50. cowabloga >= "0.4.0"
  51. crs
  52. cucumber
  53. cuid
  54. current
  55. current_web
  56. daypack-lib
  57. debian-formats
  58. decompress < "1.0.0"
  59. dkml-install-installer >= "0.4.0"
  60. dns < "4.4.1"
  61. doi2bib
  62. dose3
  63. dune-release >= "0.2.0"
  64. dunolint >= "0.0.20251006"
  65. dunolint-lib
  66. dunolint-lib-base
  67. duppy >= "0.9.4"
  68. elpi
  69. expect >= "0.1.0"
  70. expect_test_helpers_core
  71. expect_test_helpers_kernel
  72. ez_file
  73. ez_search
  74. fat-filesystem
  75. git-split < "1.0.0"
  76. gpiod
  77. graphql_parser >= "0.11.0"
  78. hardcaml_verify
  79. hardcaml_waveterm
  80. hardcaml_xilinx_components
  81. hlarp >= "0.0.3"
  82. horned_worm
  83. humane-re
  84. icalendar
  85. index
  86. index-bench
  87. irmin-bench
  88. jingoo >= "1.2.21"
  89. js_of_ocaml >= "3.10.0"
  90. js_of_ocaml-compiler >= "3.10.0"
  91. js_of_ocaml-lwt >= "3.10.0"
  92. js_of_ocaml-ocamlbuild >= "3.10.0" & < "5.0"
  93. js_of_ocaml-ppx >= "3.10.0"
  94. js_of_ocaml-ppx_deriving_json >= "3.10.0"
  95. js_of_ocaml-toplevel >= "3.10.0"
  96. js_of_ocaml-tyxml >= "3.10.0"
  97. jsonschema
  98. jwt
  99. jwto
  100. kappa-library
  101. kubecaml
  102. labrys
  103. lastfm >= "0.3.4"
  104. ldap >= "2.5.1"
  105. learn-ocaml
  106. ledes
  107. lipsum
  108. liquidsoap >= "2.3.3"
  109. liquidsoap-core >= "2.3.0"
  110. liquidsoap-lang >= "2.3.0"
  111. MlFront_Cli >= "2.1.4~prerel2" & < "2.3.1"
  112. MlFront_Core >= "2.4.2.30"
  113. MlFront_ZipFile
  114. magic-trace
  115. mdx
  116. mehari
  117. mparser-re
  118. naboris
  119. netsnmp
  120. ninja_utils
  121. nx-text
  122. obelisk >= "0.5.0"
  123. ocaml-lsp-server >= "1.9.0"
  124. ocamlformat >= "0.11.0"
  125. ocamlformat-mlx
  126. ocamlformat-rpc < "0.21.0"
  127. ocamlmig
  128. ocp-build
  129. ocp-index
  130. ocsigen-start
  131. ocsigenserver >= "5.1.0"
  132. octez-bls12-381-signature
  133. octez-libs
  134. opam-bin >= "0.9.5" & < "1.1.0"
  135. opam-client
  136. opam-compiler
  137. opam-core
  138. opam-format >= "2.0.8" & != "2.1.0~beta4"
  139. opam-lib
  140. opam-solver >= "2.0.8" & < "2.1.0" | >= "2.2.0"
  141. opam-state >= "2.2.0"
  142. opam_bin_lib
  143. opium
  144. opium_kernel
  145. oranger
  146. orun
  147. ostap
  148. ozulip
  149. pa_ppx_parsetree
  150. pa_ppx_regexp >= "0.04"
  151. pa_ppx_string
  152. patdiff
  153. pgocaml >= "2.3"
  154. pgx
  155. plato
  156. podge >= "0.3"
  157. ppx_css < "v0.17.0"
  158. ppx_cstubs
  159. ppx_expect < "v0.17.0"
  160. ppx_expect_nobase
  161. ppx_minidebug >= "1.6.0"
  162. ppx_regexp >= "0.3.2"
  163. ppx_test
  164. ppx_tyre
  165. ppxlib >= "0.21.1"
  166. prometheus >= "0.2"
  167. prometheus-app
  168. pyml_bindgen >= "0.3.1"
  169. rdf >= "0.12.0"
  170. re_parser
  171. redis
  172. regenerate
  173. regrade
  174. rfc1951 < "1.0.0"
  175. safemoney >= "0.3.0"
  176. saga
  177. sarek
  178. sarif >= "0.2.1"
  179. satyrographos >= "0.0.2.7"
  180. semantic_version
  181. sexp_pretty
  182. simple-diff
  183. slug
  184. snf_mcp
  185. soupault
  186. spoc
  187. statocaml_profile
  188. swagger
  189. talon
  190. testo
  191. testo-lwt
  192. testo-util
  193. tezos-clic >= "16.0"
  194. tezos-stdlib-unix
  195. tezt
  196. timere-parse
  197. touist >= "3.5.0"
  198. tyre >= "0.4"
  199. tyxml >= "4.2.0"
  200. tyxml-syntax
  201. uri < "4.0.0"
  202. uri-re
  203. user-agent-parser
  204. user-setup
  205. uuuu
  206. validate
  207. vendredi
  208. wasm_of_ocaml-compiler
  209. webmachine
  210. xtmpl >= "0.18.0"

Conflicts

None