-{-# OPTIONS_GHC -fno-implicit-prelude #-}
+{-# OPTIONS_GHC -XNoImplicitPrelude #-}
-----------------------------------------------------------------------------
-- |
-- Module : Text.ParserCombinators.ReadPrec
reset, -- :: ReadPrec a -> ReadPrec a
-- * Other operations
- -- All are based directly on their similarly-naned 'ReadP' counterparts.
+ -- | All are based directly on their similarly-named 'ReadP' counterparts.
get, -- :: ReadPrec Char
look, -- :: ReadPrec String
(+++), -- :: ReadPrec a -> ReadPrec a -> ReadPrec a
-- Operations over ReadPrec
lift :: ReadP a -> ReadPrec a
--- ^ Lift a precedence-insensitive 'ReadP' to a 'ReadPrec'
+-- ^ Lift a precedence-insensitive 'ReadP' to a 'ReadPrec'.
lift m = P (\_ -> m)
step :: ReadPrec a -> ReadPrec a
--- ^ Increases the precedence context by one
+-- ^ Increases the precedence context by one.
step (P f) = P (\n -> f (n+1))
reset :: ReadPrec a -> ReadPrec a
--- ^ Resets the precedence context to zero
+-- ^ Resets the precedence context to zero.
reset (P f) = P (\n -> f minPrec)
prec :: Prec -> ReadPrec a -> ReadPrec a
--- ^ @(prec n p)@ checks that the precedence context is
--- less than or equal to n,
+-- ^ @(prec n p)@ checks whether the precedence context is
+-- less than or equal to @n@, and
+--
-- * if not, fails
--- * if so, parses p in context n
+--
+-- * if so, parses @p@ in context @n@.
prec n (P f) = P (\c -> if c <= n then f n else ReadP.pfail)
-- ---------------------------------------------------------------------------
-- Derived operations
get :: ReadPrec Char
+-- ^ Consumes and returns the next character.
+-- Fails if there is no input left.
get = lift ReadP.get
look :: ReadPrec String
+-- ^ Look-ahead: returns the part of the input that is left, without
+-- consuming it.
look = lift ReadP.look
(+++) :: ReadPrec a -> ReadPrec a -> ReadPrec a
+-- ^ Symmetric choice.
P f1 +++ P f2 = P (\n -> f1 n ReadP.+++ f2 n)
(<++) :: ReadPrec a -> ReadPrec a -> ReadPrec a
+-- ^ Local, exclusive, left-biased choice: If left parser
+-- locally produces any result at all, then right parser is
+-- not used.
P f1 <++ P f2 = P (\n -> f1 n ReadP.<++ f2 n)
pfail :: ReadPrec a
+-- ^ Always fails.
pfail = lift ReadP.pfail
choice :: [ReadPrec a] -> ReadPrec a
+-- ^ Combines all parsers in the specified list.
choice ps = foldr (+++) pfail ps
-- ---------------------------------------------------------------------------