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'
        ]