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Adding 2 new combinators #25

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18 changes: 17 additions & 1 deletion Text/Parsec/Combinator.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -14,7 +14,7 @@

module Text.Parsec.Combinator
( choice
, count
, count, countUpTo, countFromTo
, between
, option, optionMaybe, optional
, skipMany1
Expand Down Expand Up @@ -165,6 +165,22 @@ count :: (Stream s m t) => Int -> ParsecT s u m a -> ParsecT s u m [a]
count n p | n <= 0 = return []
| otherwise = sequence (replicate n p)

-- | @countUpto n p@ parses zero to @n@ occurrences of @p@. If @n@ is smaller or
-- equal to zero, the parser equals to @return []@. Returns a list of up to
-- @n@ values returned by @p@.
countUpTo :: Stream s m t => Int -> ParsecT s u m a -> ParsecT s u m [a]
countUpTo n p
| n <= 0 = return []
| otherwise = option [] (liftM2 (:) p (countUpTo (pred n) p))

-- | @countUpto m n p@ parses @m@ to @n@ occurrences of @p@. If @n@ is smaller or
-- equal to zero, the parser equals to @return []@. Returns a list of @m@ to
-- @n@ values returned by @p@.
countFromTo :: Stream s m t => Int -> Int -> ParsecT s u m a -> ParsecT s u m [a]
countFromTo l r p
| r < l = return []
| otherwise = liftM2 (++) (count l p) (countUpTo (r - l) p)

-- | @chainr p op x@ parses /zero/ or more occurrences of @p@,
-- separated by @op@ Returns a value obtained by a /right/ associative
-- application of all functions returned by @op@ to the values returned
Expand Down