package re

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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. BetterErrors
  19. bancos
  20. bap-byteweight-frontend
  21. bap-callgraph-collator
  22. bap-fsi-benchmark
  23. bap-ida
  24. bap-objdump
  25. bap-print >= "2.2.0"
  26. bap-radare2
  27. benchpress
  28. bibfmt
  29. bio_io >= "0.5.1"
  30. biocaml
  31. bistro < "0.6.0"
  32. bonsai >= "v0.15.0"
  33. brot
  34. caisar >= "4.0"
  35. calculon
  36. calculon-web
  37. caldav
  38. calendar >= "3.0.0"
  39. camlp5 >= "8.02.01"
  40. camlp5-buildscripts
  41. camyll
  42. caqti >= "1.7.0"
  43. catala
  44. chamo
  45. ciao_lwt
  46. cinaps >= "v0.10.0"
  47. cohttp
  48. coin < "0.1.5"
  49. colibri2
  50. commons
  51. conan >= "0.0.6"
  52. core_bench
  53. core_extended
  54. cosovo
  55. cowabloga >= "0.4.0"
  56. crs
  57. cucumber
  58. cuid
  59. current
  60. current_web
  61. daypack-lib
  62. debian-formats
  63. decompress < "1.0.0"
  64. dns < "4.4.1"
  65. doi2bib
  66. dose3
  67. dune-glob >= "3.21.0"
  68. dune-release >= "0.2.0"
  69. dunolint >= "0.0.20251006"
  70. dunolint-lib
  71. dunolint-lib-base
  72. duppy >= "0.9.5"
  73. elpi
  74. expect >= "0.1.0"
  75. expect_test_helpers_core
  76. expect_test_helpers_kernel
  77. ez_file
  78. ez_search
  79. fat-filesystem
  80. git-split < "1.0.0"
  81. gpiod
  82. graphql_parser >= "0.11.0"
  83. hardcaml_verify
  84. hardcaml_waveterm
  85. hardcaml_xilinx_components
  86. hlarp >= "0.0.3"
  87. horned_worm
  88. humane-re
  89. icalendar
  90. index
  91. index-bench
  92. irmin-bench
  93. jingoo >= "1.2.21"
  94. js_of_ocaml >= "3.10.0"
  95. js_of_ocaml-compiler >= "3.10.0"
  96. js_of_ocaml-lwt >= "3.10.0"
  97. js_of_ocaml-ocamlbuild >= "3.10.0" & < "5.0"
  98. js_of_ocaml-ppx >= "3.10.0"
  99. js_of_ocaml-ppx_deriving_json >= "3.10.0"
  100. js_of_ocaml-toplevel >= "3.10.0"
  101. js_of_ocaml-tyxml >= "3.10.0"
  102. jsonschema
  103. jsonschema-core
  104. jsonschema-validation
  105. jwt
  106. jwto
  107. kappa-library
  108. kubecaml
  109. labrys
  110. lastfm >= "0.3.4"
  111. ldap >= "2.5.1"
  112. learn-ocaml
  113. ledes
  114. lipsum
  115. liquidsoap >= "2.3.3" & < "2.4.2"
  116. liquidsoap-core >= "2.3.0"
  117. liquidsoap-lang >= "2.3.0"
  118. lwt_lint
  119. lwt_ppx_to_let_syntax
  120. MlFront_Cli >= "2.1.4~prerel2" & < "2.3.1"
  121. MlFront_Core >= "2.4.2.30"
  122. MlFront_ZipFile
  123. magic-trace
  124. mdx
  125. mehari
  126. menhir-lsp >= "0.1.2"
  127. mparser-re
  128. naboris
  129. netsnmp
  130. ninja_utils
  131. nx-text
  132. obelisk >= "0.5.0"
  133. ocaml-lsp-server >= "1.9.0"
  134. ocamlformat >= "0.11.0"
  135. ocamlformat-mlx
  136. ocamlformat-rpc < "0.21.0"
  137. ocamlmig
  138. ocp-build
  139. ocp-index
  140. ocsigen-start
  141. ocsigenserver >= "5.1.0"
  142. opam-bin >= "0.9.5" & < "1.1.0"
  143. opam-client
  144. opam-compiler
  145. opam-core
  146. opam-format >= "2.0.8" & != "2.1.0~beta4"
  147. opam-lib
  148. opam-solver >= "2.0.8" & < "2.1.0" | >= "2.2.0"
  149. opam-state >= "2.2.0"
  150. opam_bin_lib
  151. opium
  152. opium_kernel
  153. oranger
  154. orun
  155. ostap
  156. ozulip
  157. pa_ppx_parsetree
  158. pa_ppx_regexp >= "0.04"
  159. pa_ppx_string
  160. parseff
  161. passage >= "0.3.2"
  162. patdiff
  163. pgocaml >= "2.3"
  164. pgx
  165. plato
  166. podge >= "0.3"
  167. ppx_css < "v0.17.0"
  168. ppx_cstubs
  169. ppx_expect < "v0.17.0"
  170. ppx_expect_nobase < "v0.17.3.0"
  171. ppx_mikmatch
  172. ppx_minidebug >= "1.6.0"
  173. ppx_regexp >= "0.3.2"
  174. ppx_test
  175. ppx_tyre
  176. ppxlib >= "0.21.1"
  177. prometheus >= "0.2"
  178. prometheus-app
  179. pyml_bindgen >= "0.3.1"
  180. raga
  181. rdf >= "0.12.0"
  182. re_parser
  183. redis
  184. regenerate
  185. regrade
  186. rfc1951 < "1.0.0"
  187. safemoney >= "0.3.0"
  188. saga
  189. sarek
  190. sarif >= "0.2.1"
  191. satyrographos >= "0.0.2.7"
  192. semantic_version
  193. sexp_pretty
  194. shakuhachi
  195. simple-diff
  196. slug
  197. smtml >= "0.21.0"
  198. snf_mcp
  199. soupault
  200. spectrum >= "0.7.0"
  201. spectrum_capabilities
  202. spectrum_palette_ppx
  203. spectrum_tools
  204. spoc
  205. statocaml_profile
  206. swagger
  207. talon < "1.0.0~alpha3"
  208. testcontainers
  209. testo
  210. testo-lwt
  211. testo-util
  212. tezt
  213. timere-parse
  214. touist >= "3.5.0"
  215. tyre >= "0.4"
  216. tyxml >= "4.2.0"
  217. tyxml-syntax
  218. uri < "4.0.0"
  219. uri-re
  220. user-agent-parser
  221. user-setup
  222. uuuu < "0.4.0"
  223. validate
  224. vendredi
  225. wasm_of_ocaml-compiler
  226. webmachine
  227. xtmpl >= "0.18.0"

Conflicts

None