IBAN: Difference between revisions

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This program uses the Maybe and Either monads to handle failures. Values of type 'Maybe a' can contain 'Nothing' (no value) or 'Just a' (a value of type 'a'). Values of type 'Either a b' contain 'Left b' (usually indicating failure) or 'Right c' (usually indicating success).

import Data.Char (toUpper)

validateIBAN :: String -> Either String String

validateIBAN [] = Left "No IBAN number."

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else check

where

-- remove blanks

-- remove blanks and make all letters uppercase

normalized = concat $ words xs

normalized = map toUpper $ concat $ words xs

-- get the country code

country = take 2 normalized

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validateIBAN "GB82 WEST 1234 5698 7654 32"

Right "GB82 WEST 1234 5698 7654 32"

validateIBAN "gb82 West 1234 5698 7654 32"

Right "gb82 West 1234 5698 7654 32"

validateIBAN "GB82 WEST 1234 5698 7654 31"

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Left "Invalid IBAN number GB82 WEST 1234 5698 7654 3: Number length does not match."

validateIBAN "GB82 ~~WEsT~~ 1234 5698 7654 32"

validateIBAN "GB82 _EST 1234 5698 7654 32"

Left "Invalid IBAN number GB82 ~~WEsT~~ 1234 5698 7654 32: Number contains illegal digits."

Left "Invalid IBAN number GB82 _EST 1234 5698 7654 32: Number contains illegal digits."

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