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-- | A module that exports a simple regex interface. This code is mostly copied
-- from the regex-compat package at hackage.
module Text.Hakyll.Regex
( splitRegex
, substituteRegex
) where
import Text.Regex.TDFA
-- | Match a regular expression against a string, returning more information
-- about the match.
matchRegexAll :: Regex -> String -> Maybe (String, String, String, [String])
matchRegexAll p str = matchM p str
-- | Replaces every occurance of the given regexp with the replacement string.
subRegex :: Regex -- ^ Search pattern
-> String -- ^ Input string
-> String -- ^ Replacement text
-> String -- ^ Output string
subRegex _ "" _ = ""
subRegex regexp inp replacement =
let -- bre matches a backslash then capture either a backslash or some digits
bre = makeRegex "\\\\(\\\\|[0-9]+)"
lookup' _ [] _ = []
lookup' [] _ _ = []
lookup' match' repl groups =
case matchRegexAll bre repl of
Nothing -> repl
Just (lead, _, trail, bgroups) ->
let newval =
if (head bgroups) == "\\"
then "\\"
else let index :: Int
index = (read (head bgroups)) - 1
in if index == -1
then match'
else groups !! index
in lead ++ newval ++ lookup' match' trail groups
in case matchRegexAll regexp inp of
Nothing -> inp
Just (lead, match', trail, groups) ->
lead ++ lookup' match' replacement groups ++ (subRegex regexp trail replacement)
-- | Splits a string based on a regular expression. The regular expression
-- should identify one delimiter.
splitRegex' :: Regex -> String -> [String]
splitRegex' _ [] = []
splitRegex' delim strIn = loop strIn where
loop str = case matchOnceText delim str of
Nothing -> [str]
Just (firstline, _, remainder) ->
if null remainder
then [firstline,""]
else firstline : loop remainder
-- | Split a list at a certain element.
splitRegex :: String -> String -> [String]
splitRegex pattern = filter (not . null)
. splitRegex' (makeRegex pattern)
-- | Substitute a regex. Simplified interface.
substituteRegex :: String -- ^ Pattern to replace (regex).
-> String -- ^ Replacement string.
-> String -- ^ Input string.
-> String -- ^ Result.
substituteRegex pattern replacement str = subRegex (makeRegex pattern) str replacement
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