Haskell Language Attoparsec Combinators
Example
Parsing input is best achieved through larger parser functions that are composed of smaller, single purpose ones.
Let's say we wished to parse the following text which represents working hours:
Monday: 0800 1600.
We could split these into two "tokens": the day name -- "Monday" -- and a time portion "0800" to "1600".
To parse a day name, we could write the following:
data Day = Day String day :: Parser Day day = do name <- takeWhile1 (/= ':') skipMany1 (char ':') skipSpace return $ Day name
To parse the time portion we could write:
data TimePortion = TimePortion String String
time = do
start <- takeWhile1 isDigit
skipSpace
end <- takeWhile1 isDigit
return $ TimePortion start end
Now we have two parsers for our individual parts of the text, we can combine these in a "larger" parser to read an entire day's working hours:
data WorkPeriod = WorkPeriod Day TimePortion
work = do
d <- day
t <- time
return $ WorkPeriod d t
and then run the parser:
parseOnly work "Monday: 0800 1600"
