131 lines
4.0 KiB
Haskell
131 lines
4.0 KiB
Haskell
{-# LANGUAGE ScopedTypeVariables #-}
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{-|
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Easy regular expression helpers, currently based on regex-tdfa. These should:
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- be cross-platform, not requiring C libraries
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- support unicode
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- support extended regular expressions
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- support replacement, with backreferences etc.
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- support splitting
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- have mnemonic names
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- have simple monomorphic types
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- work with strings
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Current limitations:
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- (?i) and similar are not supported
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-}
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module Hledger.Utils.Regex (
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-- * type aliases
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Regexp
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,Replacement
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-- * standard regex operations
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,regexMatches
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,regexMatchesCI
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,regexReplace
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,regexReplaceCI
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,regexReplaceBy
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,regexReplaceByCI
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)
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where
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import Data.Array
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import Data.Char
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import Data.List (foldl')
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import Text.Regex.TDFA (
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Regex, CompOption(..), ExecOption(..), defaultCompOpt, defaultExecOpt,
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makeRegexOpts, AllMatches(getAllMatches), match, (=~), MatchText
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)
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-- import Hledger.Utils.Debug
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import Hledger.Utils.UTF8IOCompat (error')
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-- | Regular expression. Extended regular expression-ish syntax ? But does not support eg (?i) syntax.
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type Regexp = String
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-- | A replacement pattern. May include numeric backreferences (\N).
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type Replacement = String
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-- | Convert our string-based regexps to real ones. Can fail if the
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-- string regexp is malformed.
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toRegex :: Regexp -> Regex
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toRegex = makeRegexOpts compOpt execOpt
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toRegexCI :: Regexp -> Regex
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toRegexCI = makeRegexOpts compOpt{caseSensitive=False} execOpt
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compOpt :: CompOption
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compOpt = defaultCompOpt
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execOpt :: ExecOption
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execOpt = defaultExecOpt
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-- regexMatch' :: RegexContext Regexp String a => Regexp -> String -> a
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-- regexMatch' r s = s =~ (toRegex r)
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regexMatches :: Regexp -> String -> Bool
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regexMatches = flip (=~)
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regexMatchesCI :: Regexp -> String -> Bool
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regexMatchesCI r = match (toRegexCI r)
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-- | Replace all occurrences of the regexp, transforming each match with the given function.
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regexReplaceBy :: Regexp -> (String -> String) -> String -> String
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regexReplaceBy r = replaceAllBy (toRegex r)
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regexReplaceByCI :: Regexp -> (String -> String) -> String -> String
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regexReplaceByCI r = replaceAllBy (toRegexCI r)
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-- | Replace all occurrences of the regexp with the replacement
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-- pattern. The replacement pattern supports numeric backreferences
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-- (\N) but no other RE syntax.
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regexReplace :: Regexp -> Replacement -> String -> String
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regexReplace re = replaceRegex (toRegex re)
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regexReplaceCI :: Regexp -> Replacement -> String -> String
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regexReplaceCI re = replaceRegex (toRegexCI re)
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--
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replaceRegex :: Regex -> Replacement -> String -> String
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replaceRegex re repl s = foldl (replaceMatch repl) s (reverse $ match re s :: [MatchText String])
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replaceMatch :: Replacement -> String -> MatchText String -> String
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replaceMatch replpat s matchgroups = pre ++ repl ++ post
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where
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((_,(off,len)):_) = elems matchgroups -- groups should have 0-based indexes, and there should always be at least one, since this is a match
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(pre, post') = splitAt off s
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post = drop len post'
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repl = replaceAllBy (toRegex "\\\\[0-9]+") (replaceBackReference matchgroups) replpat
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replaceBackReference :: MatchText String -> String -> String
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replaceBackReference grps ('\\':s@(_:_)) | all isDigit s =
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case read s of n | n `elem` indices grps -> fst (grps ! n)
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_ -> error' $ "no match group exists for backreference \"\\"++s++"\""
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replaceBackReference _ s = error' $ "replaceBackReference called on non-numeric-backreference \""++s++"\", shouldn't happen"
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--
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-- http://stackoverflow.com/questions/9071682/replacement-substition-with-haskell-regex-libraries :
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-- | Replace all occurrences of a regexp in a string, transforming each match with the given function.
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replaceAllBy :: Regex -> (String -> String) -> String -> String
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replaceAllBy re f s = start end
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where
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(_, end, start) = foldl' go (0, s, id) $ (getAllMatches $ match re s :: [(Int, Int)])
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go (ind,read,write) (off,len) =
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let (skip, start) = splitAt (off - ind) read
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(matched, remaining) = splitAt len start
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in (off + len, remaining, write . (skip++) . (f matched ++))
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