HORIZON HASKELLDocslts/ghc-10.0.x8c2f8e82026-10-19Search names, modules, packages, or :: a typeCtrl K

GHC 10.0.0.20260917 · lts/ghc-10.0.x · 8c2f8e8 · 2026-10-19

Modulehledger-lib-1.52.4GHC2021

Hledger.Utils.Regex

Easy regular expression helpers, currently based on regex-tdfa. These should:

  • be cross-platform, not requiring C libraries

  • support unicode

  • support extended regular expressions

  • support replacement, with backreferences etc.

  • support splitting

  • have mnemonic names

  • have simple monomorphic types

  • work with simple strings

Regex strings are automatically compiled into regular expressions the first time they are seen, and these are cached. If you use a huge number of unique regular expressions this might lead to increased memory usage. Several functions have memoised variants (*Memo), which also trade space for time.

Currently two APIs are provided:

  • The old partial one (with ' suffixes') which will call error on any problem (eg with malformed regexps). This comes from hledger's origin as a command-line tool.

  • The new total one which will return an error message. This is better for long-running apps like hledger-web.

Current limitations:

  • (?i) and similar are not supported

  • 3 types
  • 11 values

Regexp type and constructors

6 declarations
datadata Regexp
#

Regular expression. Extended regular expression-ish syntax ? But does not support eg (?i) syntax.

Instances8Eq, Ord, Read, Show, NFData, ToJSON, …

type aliases

2 declarations
typetype Replacement = String
#

A replacement pattern. May include numeric backreferences (N).

typetype RegexError = String
#

An error message arising during a regular expression operation. Eg: trying to compile a malformed regular expression, or trying to apply a malformed replacement pattern.

total regex operations

6 declarations
valueregexMatchText :: Regexp -> Text -> Bool
#

Tests whether a Regexp matches a Text.

This currently unpacks the Text to a String, to work around a performance bug in regex-tdfa (#9), which may or may not be relevant here.

valueregexReplace :: Regexp -> Replacement -> String -> Either RegexError String
#

A memoising version of regexReplace. Caches the result for each search pattern, replacement pattern, target string tuple. This won't generate a regular expression parsing error since that is pre-compiled nowadays, but there can still be a runtime error from the replacement pattern, eg with a backreference referring to a nonexistent match group.