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;lib: regexReplace: note the kind of RegexError still possible

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Simon Michael 2020-11-24 09:16:08 -08:00
parent 221a6d9001
commit 9b9f2543d8
1 changed files with 9 additions and 2 deletions
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11
hledger-lib/Hledger/Utils/Regex.hs
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@ -162,13 +162,20 @@ regexMatch = matchTest
-- | 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.
regexReplace :: Regexp -> Replacement -> String -> Either RegexError String
regexReplace re repl = memo $ regexReplaceUnmemo re repl
-- helpers:
-- Replace this regular expression with this replacement pattern in this
-- string, or return an error message.
-- string, or return an error message. (There should be no regexp
-- parsing errors these days since Regexp's compiled form is used,
-- but there can still be a runtime error from the replacement
-- pattern, eg a backreference referring to a nonexistent match group.)
regexReplaceUnmemo :: Regexp -> Replacement -> String -> Either RegexError String
regexReplaceUnmemo re repl s = foldM (replaceMatch repl) s (reverse $ match (reCompiled re) s :: [MatchText String])
where
@ -190,7 +197,7 @@ regexReplaceUnmemo re repl s = foldM (replaceMatch repl) s (reverse $ match (reC
-- return the referenced group text, or an error message.
lookupMatchGroup :: MatchText String -> String -> Either RegexError String
lookupMatchGroup grps ('\\':s@(_:_)) | all isDigit s =
case read s of n | n `elem` indices grps -> Right $ fst (grps ! n)
case read s of n | n `elem` indices grps -> Right $ fst (grps ! n) -- PARTIAL: should not fail, all digits
_ -> Left $ "no match group exists for backreference \"\\"++s++"\""
lookupMatchGroup _ s = Left $ "lookupMatchGroup called on non-numeric-backreference \""++s++"\", shouldn't happen"
backrefRegex = toRegex' "\\\\[0-9]+" -- PARTIAL: should not fail