regex-wrapper: Types that can only be constructed if they match a regular expression

[ bsd3, data, library ] [ Propose Tags ]

Provides tooling for working with types whose values must match a regular expression provided in the type.

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Dependencies aeson, base (>= && <4.13), bytestring, containers, hashable, regex-tdfa, string-conv, text [details]
License BSD-3-Clause
Copyright (c) 2019 Luke Clifton
Author Luke Clifton
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Source repo head: git clone
Uploaded by lukec at 2019-11-11T06:39:13Z
Distributions NixOS:
Downloads 321 total (2 in the last 30 days)
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Status Hackage Matrix CI
Docs available [build log]
Last success reported on 2019-11-11 [all 1 reports]


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This library allows you to create types that are guaranteed to contain a string that matches a given regular expression which is expressed at the type level.

newtype User = User (Matched String "^[a-zA-Z0-9]{4,15}$")

parseUser :: String -> Either (RegexError String) User
parseUser = fmap User . parseMatchedEither

prettyUser :: User -> String
prettyUser (User m) = asString m

main :: IO ()
main = do
    l <- getLine
    case parseUser l of
        Right user -> putStrLn $ "Hello, " ++ prettyUser user ++ "!"
        Left error -> putStrLn $ "Could not parse username: " ++ prettyRegexError  error
Could not parse username: The input "bad" did not match the pattern ^[a-zA-Z0-9]{4,15}$
Hello, good!