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. alice
  6. atd >= "2.2.1"
  7. atd-jsonlike
  8. atdcpp
  9. atdd
  10. atdgen >= "2.3.3"
  11. atdgen-runtime = "2.2.1"
  12. atdj >= "2.2.1"
  13. atdpy >= "2.4.1"
  14. atds < "2.3.3"
  15. atdts
  16. aws-config
  17. awsm-codegen
  18. awso
  19. BetterErrors
  20. bancos
  21. bap-byteweight-frontend
  22. bap-callgraph-collator
  23. bap-fsi-benchmark
  24. bap-ida
  25. bap-objdump
  26. bap-print
  27. bap-radare2
  28. bibfmt
  29. bio_io >= "0.5.1"
  30. biocaml
  31. bonsai >= "v0.15.0"
  32. brot
  33. caisar >= "4.0"
  34. calculon
  35. calculon-web
  36. caldav
  37. calendar >= "3.0.0"
  38. camlp5 >= "8.02.01"
  39. camlp5-buildscripts
  40. camyll
  41. caqti >= "1.7.0"
  42. catala
  43. chamo
  44. ciao_lwt
  45. cinaps
  46. cohttp
  47. coin < "0.1.5"
  48. colibri2
  49. commons
  50. conan >= "0.0.6"
  51. core_bench
  52. core_extended
  53. cosovo
  54. cowabloga >= "0.4.0"
  55. crs
  56. cucumber
  57. cuid
  58. current
  59. current_web
  60. daypack-lib
  61. debian-formats
  62. decompress < "1.0.0"
  63. dns < "4.4.1"
  64. doi2bib
  65. dose3
  66. dune-glob >= "3.21.0"
  67. dune-release >= "0.2.0"
  68. dunolint >= "0.0.20251006"
  69. dunolint-lib
  70. dunolint-lib-base
  71. duppy >= "0.9.5"
  72. elpi
  73. expect >= "0.1.0"
  74. expect_test_helpers_core
  75. expect_test_helpers_kernel
  76. ez_file
  77. ez_search
  78. fat-filesystem
  79. git-split < "1.0.0"
  80. gpiod
  81. graphql_parser >= "0.11.0"
  82. hardcaml_verify
  83. hardcaml_waveterm
  84. hardcaml_xilinx_components
  85. hlarp >= "0.0.3"
  86. humane-re
  87. icalendar
  88. index
  89. index-bench
  90. irmin-bench
  91. jingoo >= "1.2.21"
  92. js_of_ocaml >= "3.10.0"
  93. js_of_ocaml-compiler >= "3.10.0"
  94. js_of_ocaml-lwt >= "3.10.0"
  95. js_of_ocaml-ocamlbuild >= "3.10.0" & < "5.0"
  96. js_of_ocaml-ppx >= "3.10.0"
  97. js_of_ocaml-ppx_deriving_json >= "3.10.0"
  98. js_of_ocaml-toplevel >= "3.10.0"
  99. js_of_ocaml-tyxml >= "3.10.0"
  100. jsonschema
  101. jsonschema-core
  102. jsonschema-validation
  103. jwt
  104. jwto
  105. kappa-library
  106. kubecaml
  107. lastfm >= "0.3.4"
  108. ldap >= "2.5.1"
  109. learn-ocaml
  110. ledes
  111. lipsum
  112. liquidsoap >= "2.3.3" & < "2.4.2"
  113. liquidsoap-core >= "2.3.0"
  114. liquidsoap-lang >= "2.3.0"
  115. lwt_ppx_to_let_syntax
  116. MlFront_Cli >= "2.1.4~prerel2" & < "2.3.1"
  117. MlFront_Core >= "2.4.2.30"
  118. MlFront_ZipFile
  119. magic-trace
  120. mdx
  121. mehari
  122. menhir-lsp >= "0.1.2"
  123. mparser-re
  124. naboris
  125. netsnmp
  126. ninja_utils
  127. nx-text
  128. obelisk >= "0.5.0"
  129. ocaml-lsp-server >= "1.9.0"
  130. ocamlformat
  131. ocamlformat-mlx
  132. ocamlformat-rpc < "0.21.0"
  133. ocamlmig
  134. ocgtk
  135. ocp-build
  136. ocp-index
  137. ocsigen-start
  138. ocsigenserver >= "5.1.0"
  139. opam-bin >= "0.9.5" & < "1.1.0"
  140. opam-client
  141. opam-compiler
  142. opam-core
  143. opam-format >= "2.0.8" & != "2.1.0~beta4"
  144. opam-lib
  145. opam-solver >= "2.0.8" & < "2.1.0" | >= "2.2.0"
  146. opam-state >= "2.2.0"
  147. opam_bin_lib
  148. opium
  149. opium_kernel
  150. oranger
  151. orun
  152. ostap
  153. ozulip
  154. pa_ppx_parsetree
  155. pa_ppx_regexp >= "0.04"
  156. pa_ppx_string
  157. parseff
  158. passage >= "0.3.2"
  159. patdiff
  160. pgocaml >= "2.3"
  161. pgx
  162. plato
  163. podge >= "0.3"
  164. ppx_css < "v0.17.0"
  165. ppx_cstubs
  166. ppx_expect < "v0.17.0"
  167. ppx_expect_nobase < "v0.17.3.0"
  168. ppx_mikmatch
  169. ppx_minidebug >= "1.6.0"
  170. ppx_regexp >= "0.3.2"
  171. ppx_test
  172. ppx_tyre
  173. ppxlib >= "0.21.1"
  174. prometheus >= "0.2"
  175. prometheus-app
  176. pyml_bindgen >= "0.3.1"
  177. raga
  178. rdf
  179. re_parser
  180. redis
  181. regrade
  182. rfc1951 < "1.0.0"
  183. safemoney >= "0.3.0"
  184. saga
  185. sarek
  186. sarif >= "0.2.1"
  187. satyrographos
  188. semantic_version
  189. sexp_pretty
  190. shakuhachi
  191. simple-diff
  192. slug
  193. smtml >= "0.21.0"
  194. snf_mcp
  195. soupault
  196. spectrum >= "0.7.0"
  197. spectrum_capabilities
  198. spectrum_palette_ppx
  199. spectrum_tools
  200. spoc
  201. statocaml_profile
  202. stem
  203. swagger
  204. talon < "1.0.0~alpha3"
  205. testcontainers
  206. testo
  207. testo-lwt
  208. testo-util
  209. tezt
  210. timere-parse
  211. touist >= "3.5.0"
  212. tyre >= "0.4"
  213. tyxml >= "4.2.0"
  214. tyxml-syntax
  215. uri < "4.0.0"
  216. uri-re
  217. user-agent-parser
  218. user-setup
  219. uuuu < "0.4.0"
  220. validate
  221. vendredi
  222. wasm_of_ocaml-compiler
  223. webmachine
  224. wire
  225. xtmpl >= "0.18.0"

Conflicts

None