Re: [Haskell-cafe] Automatically generate sum type members -> [String]

Hi, Am Dienstag, den 19.05.2015, 12:03 +0300 schrieb Anatoly Zaretsky:

On Tue, May 19, 2015 at 2:20 AM, Cody Goodman wrote:

...

data Codes = A0100A | A0500A deriving Show

codeExists "A0100A" = True codeExists "A0500A" = True codeExists _ = False

data Codes = A0100A | A0500A deriving Read

codeExists code = case reads code of [(_, "")] -> True _ -> False

Or with -XPatternGuards:

codeExists code | [(_, "")] <- reads code = True | otherwise = False

since base-4.6, there is readMaybe :: Read a => String -> Maybe a in Text.Read. So it might be nicer to write codeExists code = isJust (readMaybe code :: Maybe Codes) Greetings, Joachim -- Joachim “nomeata” Breitner mail@joachim-breitner.de • http://www.joachim-breitner.de/ Jabber: nomeata@joachim-breitner.de • GPG-Key: 0xF0FBF51F Debian Developer: nomeata@debian.org