Replace.Attoparsec.Text

Replace.Attoparsec is for finding text patterns, and also editing and replacing the found patterns. This activity is traditionally done with regular expressions, but Replace.Attoparsec uses Data.Attoparsec parsers instead for the pattern matching.

Replace.Attoparsec can be used in the same sort of “pattern capture” or “find all” situations in which one would use Python re.findall, or Perl m//, or Unix grep.

Replace.Attoparsec can be used in the same sort of “stream editing” or “search-and-replace” situations in which one would use Python re.sub, or Perl s///, or Unix sed, or awk.

See the replace-attoparsec package README for usage examples.

Parser combinator

sepCap

Arguments

:: Parser a

The pattern matching parser sep

-> Parser [Either Text a]

Separate and capture

Parser combinator to find all of the non-overlapping ocurrences of the pattern sep in a text stream. The sepCap parser will always consume its entire input and can never fail.

Output

The input stream is separated and output into a list of sections:

• Sections which can parsed by the pattern sep will be parsed and captured as Right
• Non-matching sections of the stream will be captured in Left.

The output list also has these properties:

• If the input is "" then the output list will be [].
• If there are no pattern matches, then the entire input stream will be returned as one non-matching Left section.
• The output list will not contain two consecutive Left sections.

Zero-width matches forbidden

If the pattern matching parser sep would succeed without consuming any input then sepCap will force it to fail. If we allow sep to match a zero-width pattern, then it can match the same zero-width pattern again at the same position on the next iteration, which would result in an infinite number of overlapping pattern matches.

Notes

This sepCap parser combinator is the basis for all of the other features of this module.

It is similar to the sep* family of functions found in parser-combinators and parsers but, importantly, it returns the parsed result of the sep parser instead of throwing it away, like manyTill_.

findAll

Arguments

:: Parser a

The pattern matching parser sep

-> Parser [Either Text Text]

Find all occurences

Parser combinator for finding all occurences of a pattern in a stream.

Will call sepCap with the match combinator and return the text which matched the pattern parser sep in the Right sections.

Definition:

findAll sep = (fmap.fmap) (second fst) $ sepCap (match sep)

findAllCap

Arguments

:: Parser a

The pattern matching parser sep

-> Parser [Either Text (Text, a)]

Find all occurences, parse and capture pattern matches

Parser combinator for finding all occurences of a pattern in a stream.

Will call sepCap with the match combinator so that the text which matched the pattern parser sep will be returned in the Right sections, along with the result of the parse of sep.

Definition:

findAllCap sep = sepCap (match sep)

Running parser

streamEdit

Arguments

:: Parser a

The parser sep for the pattern of interest.

-> (a -> Text)

The editor function. Takes a parsed result of sep and returns a new stream section for the replacement.

-> Text

The input stream of text to be edited.

-> Text

Stream editor

Also known as “find-and-replace”, or “match-and-substitute”. Finds all of the sections of the stream which match the pattern sep, and replaces them with the result of the editor function.

This function is not a “parser combinator,” it is a “way to run a parser”, like parse or parseOnly.

Access the matched section of text in the editor

If you want access to the matched string in the editor function, then combine the pattern parser sep with match. This will effectively change the type of the editor function to (Text,a) -> Text.

This allows us to write an editor function which can choose to not edit the match and just leave it as it is. If the editor function returns the first item in the tuple, then streamEdit will not change the matched string.

So, for all sep:

streamEdit (match sep) fst ≡ id

streamEditT

Arguments

:: Monad m

=> Parser a

The parser sep for the pattern of interest.

-> (a -> m Text)

The editor function. Takes a parsed result of sep and returns a new stream section for the replacement.

-> Text

The input stream of text to be edited.

-> m Text

Stream editor transformer

Monad transformer version of streamEdit.

The editor function will run in the underlying monad context.

If you want to do IO operations in the editor function then run this in IO.

If you want the editor function to remember some state, then run this in a stateful monad.