Writing parsers with Text.ParserCombinators

Question

In class, we wrote parsers by defining our own Parser type and this gave us a lot of flexibility. For example, if we wanted to make code and parse out "[at]" as '@', we could write

atParser = Parser $ \s ->
    case s of
        w:x:y:z:zs ->
            | (w:x:y:z:[]) == "[at]" = ['@',zs]
            | otherwise = []
        zs -> []

However, I cannot figure out how to implement this sort of parser using Text.ParserCombinators. Is it possible?

Thanks

hao · Accepted Answer · 2016-01-25 03:53:16Z

1

I believe you're looking for the string combinator.

λ> :set -package parsec
package flags have changed, resetting and loading new packages...

λ> import Text.Parsec

λ> :t string
string :: Stream s m Char => String -> ParsecT s u m String

λ> parse (string "[at]") "" "[at]"
Right "[at]"

λ> parse (string "[at]") "" "[at"
Left (line 1, column 1):
unexpected end of input
expecting "[at]"

λ> parse ('@' <$ string "[at]") "" "[at]"
Right '@'

answered Jan 25, 2016 at 3:53

hao

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