1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
|
{-# LANGUAGE Trustworthy #-}
{-# LANGUAGE NoImplicitPrelude #-}
-----------------------------------------------------------------------------
-- |
-- Module : Text.ParserCombinators.ReadPrec
-- Copyright : (c) The University of Glasgow 2002
-- License : BSD-style (see the file libraries/base/LICENSE)
--
-- Maintainer : libraries@haskell.org
-- Stability : provisional
-- Portability : non-portable (uses Text.ParserCombinators.ReadP)
--
-- This library defines parser combinators for precedence parsing.
-----------------------------------------------------------------------------
module Text.ParserCombinators.ReadPrec
(
ReadPrec,
-- * Precedences
Prec,
minPrec,
-- * Precedence operations
lift,
prec,
step,
reset,
-- * Other operations
-- | All are based directly on their similarly-named 'ReadP' counterparts.
get,
look,
(+++),
(<++),
pfail,
choice,
-- * Converters
readPrec_to_P,
readP_to_Prec,
readPrec_to_S,
readS_to_Prec,
)
where
import Text.ParserCombinators.ReadP
( ReadP
, ReadS
, readP_to_S
, readS_to_P
)
import qualified Text.ParserCombinators.ReadP as ReadP
( get
, look
, (+++), (<++)
, pfail
)
import GHC.Num( Num(..) )
import GHC.Base
import qualified Control.Monad.Fail as MonadFail
-- ---------------------------------------------------------------------------
-- The readPrec type
newtype ReadPrec a = P (Prec -> ReadP a)
-- Functor, Monad, MonadPlus
-- | @since 2.01
instance Functor ReadPrec where
fmap h (P f) = P (\n -> fmap h (f n))
-- | @since 4.6.0.0
instance Applicative ReadPrec where
pure x = P (\_ -> pure x)
(<*>) = ap
liftA2 = liftM2
-- | @since 2.01
instance Monad ReadPrec where
fail s = P (\_ -> fail s)
P f >>= k = P (\n -> do a <- f n; let P f' = k a in f' n)
-- | @since 4.9.0.0
instance MonadFail.MonadFail ReadPrec where
fail s = P (\_ -> MonadFail.fail s)
-- | @since 2.01
instance MonadPlus ReadPrec
-- | @since 4.6.0.0
instance Alternative ReadPrec where
empty = pfail
(<|>) = (+++)
-- precedences
type Prec = Int
minPrec :: Prec
minPrec = 0
-- ---------------------------------------------------------------------------
-- Operations over ReadPrec
lift :: ReadP a -> ReadPrec a
-- ^ Lift a precedence-insensitive 'ReadP' to a 'ReadPrec'.
lift m = P (\_ -> m)
step :: ReadPrec a -> ReadPrec a
-- ^ 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.
reset (P f) = P (\_ -> f minPrec)
prec :: Prec -> ReadPrec a -> ReadPrec a
-- ^ @(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@.
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
-- ---------------------------------------------------------------------------
-- Converting between ReadPrec and Read
readPrec_to_P :: ReadPrec a -> (Int -> ReadP a)
readPrec_to_P (P f) = f
readP_to_Prec :: (Int -> ReadP a) -> ReadPrec a
readP_to_Prec f = P f
readPrec_to_S :: ReadPrec a -> (Int -> ReadS a)
readPrec_to_S (P f) n = readP_to_S (f n)
readS_to_Prec :: (Int -> ReadS a) -> ReadPrec a
readS_to_Prec f = P (\n -> readS_to_P (f n))
|
