Regular Expressions in Idris

Regular expressions in Idris can be implemented using the Text.Regex module. Here are some examples of common regex-related tasks in Idris.

import Text.Regex

main : IO ()
main = do
    -- This tests whether a pattern matches a string.
    let match = case (find (regex "p([a-z]+)ch") "peach") of
                    Just _  -> True
                    Nothing -> False
    putStrLn $ "Match: " ++ show match

    -- For other regex tasks, we'll use a compiled Regex.
    let r = regex "p([a-z]+)ch"

    -- Many methods are available on these Regex values.
    -- Here's a match test like we saw earlier.
    putStrLn $ "MatchString: " ++ show (isJust $ find r "peach")

    -- This finds the match for the regex.
    putStrLn $ "FindString: " ++ fromMaybe "" (extract <$> find r "peach punch")

    -- The Submatch variants include information about
    -- both the whole-pattern matches and the submatches
    -- within those matches.
    putStrLn $ "FindStringSubmatch: " ++ show (groups <$> find r "peach punch")

    -- The All variants of these functions apply to all
    -- matches in the input, not just the first.
    putStrLn $ "FindAllString: " ++ show (map extract $ findAll r "peach punch pinch")

    -- The regex package can also be used to replace
    -- subsets of strings with other values.
    putStrLn $ "ReplaceAllString: " ++ replace r "<fruit>" "a peach"

    -- The Func variant allows you to transform matched
    -- text with a given function.
    let toUpper = pack . map toUpper . unpack
    putStrLn $ "ReplaceAllStringFunc: " ++ replaceAll r toUpper "a peach"

Note that Idris doesn’t have a built-in regular expression library as robust as Go’s. The Text.Regex module provides basic regex functionality, but some advanced features might not be available or might require different implementations.

To run the program, save it as regular-expressions.idr and use the Idris compiler:

$ idris regular-expressions.idr -o regular-expressions
$ ./regular-expressions
Match: True
MatchString: True
FindString: peach
FindStringSubmatch: Just ["peach", "ea"]
FindAllString: ["peach", "punch", "pinch"]
ReplaceAllString: a <fruit>
ReplaceAllStringFunc: a PEACH

This example demonstrates basic regex operations in Idris. However, it’s important to note that Idris’s regex support might not be as comprehensive as Go’s. For more advanced use cases, you might need to implement additional functionality or use external libraries.

For a complete reference on Idris regular expressions, check the Text.Regex module documentation in the Idris standard library.

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Regular Expressions in Idris