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module LearnParsers where
import Text.Trifecta
stop :: Parser a
stop = unexpected "stop"
-- read a single character '1'
one = char '1'
-- read a single character '1', then die
one' = one >> stop
-- equivalent to char '1' >> stop
-- read two characters, '1', and '2'
oneTwo = char '1' >> char '2'
-- read two characters,
-- '1' and '2', then die
oneTwo' = oneTwo >> stop
testParse :: Parser Char -> IO ()
testParse p = print $ parseString p mempty "123"
pNL s = putStrLn ('\n' : s)
oneTwoThree :: Parser String
oneTwoThree = choice
[ string "123"
, string "12"
, string "1"
]
oneTwoThree' = oneTwoThree >> stop
testParse' :: Parser String -> IO ()
testParse' p = print $ parseString p mempty "123"
oneTwoThree'' :: Parser Char
oneTwoThree'' = choice
[ one
, oneTwo
, char '1' >> char '2' >> char '3'
]
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