| 1 | """
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| 2 | tdop.py
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| 3 | """
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| 4 |
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| 5 | from _devbuild.gen.typed_arith_asdl import arith_expr_t
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| 6 | from typing import (Dict, List, Callable, Optional, Iterator, Tuple, NoReturn)
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| 7 | from typing import TYPE_CHECKING
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| 8 |
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| 9 | class ParseError(Exception):
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| 10 | pass
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| 11 |
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| 12 |
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| 13 | #
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| 14 | # Default parsing functions give errors
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| 15 | #
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| 16 |
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| 17 | def NullError(p, token, bp):
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| 18 | # type: (Parser, Token, int) -> NoReturn
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| 19 | raise ParseError("%s can't be used in prefix position" % token)
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| 20 |
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| 21 |
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| 22 | def LeftError(p, token, left, rbp):
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| 23 | # type: (Parser, Token, arith_expr_t, int) -> NoReturn
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| 24 | # Hm is this not called because of binding power?
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| 25 | raise ParseError("%s can't be used in infix position" % token)
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| 26 |
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| 27 |
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| 28 | #
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| 29 | # Input
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| 30 | #
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| 31 |
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| 32 | class Token(object):
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| 33 | def __init__(self, type, val, loc=None):
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| 34 | # type: (str, str, Optional[Tuple[int, int]]) -> None
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| 35 | self.type = type
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| 36 | self.val = val
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| 37 |
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| 38 | def __repr__(self):
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| 39 | # type: () -> str
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| 40 | return '<Token %s %s>' % (self.type, self.val)
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| 41 |
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| 42 |
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| 43 | #
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| 44 | # Parser definition
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| 45 | #
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| 46 |
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| 47 | class LeftInfo(object):
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| 48 | """Row for operator.
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| 49 |
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| 50 | In C++ this should be a big array.
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| 51 | """
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| 52 | def __init__(self, led=None, lbp=0, rbp=0):
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| 53 | # type: (Optional[LeftFunc], int, int) -> None
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| 54 | self.led = led or LeftError
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| 55 | self.lbp = lbp
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| 56 | self.rbp = rbp
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| 57 |
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| 58 |
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| 59 | class NullInfo(object):
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| 60 | """Row for operator.
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| 61 |
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| 62 | In C++ this should be a big array.
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| 63 | """
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| 64 | def __init__(self, nud=None, bp=0):
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| 65 | # type: (Optional[NullFunc], int) -> None
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| 66 | self.nud = nud or NullError
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| 67 | self.bp = bp
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| 68 |
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| 69 |
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| 70 | class ParserSpec(object):
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| 71 | """Specification for a TDOP parser."""
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| 72 |
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| 73 | def __init__(self):
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| 74 | # type: () -> None
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| 75 | self.null_lookup = {} # type: Dict[str, NullInfo]
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| 76 | self.left_lookup = {} # type: Dict[str, LeftInfo]
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| 77 |
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| 78 | def Null(self, bp, nud, tokens):
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| 79 | # type: (int, NullFunc, List[str]) -> None
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| 80 | """Register a token that doesn't take anything on the left.
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| 81 |
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| 82 | Examples: constant, prefix operator, error.
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| 83 | """
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| 84 | for token in tokens:
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| 85 | self.null_lookup[token] = NullInfo(nud=nud, bp=bp)
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| 86 | if token not in self.left_lookup:
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| 87 | self.left_lookup[token] = LeftInfo() # error
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| 88 |
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| 89 | def _RegisterLed(self, lbp, rbp, led, tokens):
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| 90 | # type: (int, int, LeftFunc, List[str]) -> None
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| 91 | for token in tokens:
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| 92 | if token not in self.null_lookup:
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| 93 | self.null_lookup[token] = NullInfo(NullError)
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| 94 | self.left_lookup[token] = LeftInfo(lbp=lbp, rbp=rbp, led=led)
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| 95 |
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| 96 | def Left(self, bp, led, tokens):
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| 97 | # type: (int, LeftFunc, List[str]) -> None
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| 98 | """Register a token that takes an expression on the left."""
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| 99 | self._RegisterLed(bp, bp, led, tokens)
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| 100 |
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| 101 | def LeftRightAssoc(self, bp, led, tokens):
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| 102 | # type: (int, LeftFunc, List[str]) -> None
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| 103 | """Register a right associative operator."""
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| 104 | self._RegisterLed(bp, bp-1, led, tokens)
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| 105 |
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| 106 | def LookupNull(self, token):
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| 107 | # type: (str) -> NullInfo
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| 108 | """Get the parsing function and precedence for a null position token."""
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| 109 | try:
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| 110 | nud = self.null_lookup[token]
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| 111 | except KeyError:
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| 112 | raise ParseError('Unexpected token %r' % token)
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| 113 | return nud
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| 114 |
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| 115 | def LookupLeft(self, token):
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| 116 | # type: (str) -> LeftInfo
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| 117 | """Get the parsing function and precedence for a left position token."""
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| 118 | try:
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| 119 | led = self.left_lookup[token]
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| 120 | except KeyError:
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| 121 | raise ParseError('Unexpected token %r' % token)
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| 122 | return led
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| 123 |
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| 124 |
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| 125 | EOF_TOKEN = Token('eof', 'eof')
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| 126 |
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| 127 |
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| 128 | class Parser(object):
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| 129 | """Recursive TDOP parser."""
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| 130 |
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| 131 | def __init__(self, spec, lexer):
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| 132 | # type: (ParserSpec, Iterator[Token]) -> None
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| 133 | self.spec = spec
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| 134 | self.lexer = lexer # iterable
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| 135 | self.token = Token('undefined', '') # current token
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| 136 |
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| 137 | def AtToken(self, token_type):
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| 138 | # type: (str) -> bool
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| 139 | """Test if we are looking at a token."""
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| 140 | return self.token.type == token_type
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| 141 |
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| 142 | def Next(self):
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| 143 | # type: () -> None
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| 144 | """Move to the next token."""
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| 145 | try:
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| 146 | t = self.lexer.next()
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| 147 | except StopIteration:
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| 148 | t = EOF_TOKEN
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| 149 | self.token = t
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| 150 |
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| 151 | def Eat(self, val):
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| 152 | # type: (str) -> None
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| 153 | """Assert the value of the current token, then move to the next token."""
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| 154 | if val and not self.AtToken(val):
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| 155 | raise ParseError('expected %s, got %s' % (val, self.token))
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| 156 | self.Next()
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| 157 |
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| 158 | def ParseUntil(self, rbp):
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| 159 | # type: (int) -> arith_expr_t
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| 160 | """
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| 161 | Parse to the right, eating tokens until we encounter a token with binding
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| 162 | power LESS THAN OR EQUAL TO rbp.
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| 163 | """
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| 164 | if self.AtToken('eof'):
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| 165 | raise ParseError('Unexpected end of input')
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| 166 |
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| 167 | t = self.token
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| 168 | self.Next() # skip over the token, e.g. ! ~ + -
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| 169 |
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| 170 | null_info = self.spec.LookupNull(t.type)
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| 171 | node = null_info.nud(self, t, null_info.bp)
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| 172 |
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| 173 | while True:
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| 174 | t = self.token
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| 175 | left_info = self.spec.LookupLeft(t.type)
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| 176 |
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| 177 | # Examples:
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| 178 | # If we see 1*2+ , rbp = 27 and lbp = 25, so stop.
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| 179 | # If we see 1+2+ , rbp = 25 and lbp = 25, so stop.
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| 180 | # If we see 1**2**, rbp = 26 and lbp = 27, so keep going.
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| 181 | if rbp >= left_info.lbp:
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| 182 | break
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| 183 | self.Next() # skip over the token, e.g. / *
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| 184 |
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| 185 | node = left_info.led(self, t, node, left_info.rbp)
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| 186 |
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| 187 | return node
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| 188 |
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| 189 | def Parse(self):
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| 190 | # type: () -> arith_expr_t
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| 191 | self.Next()
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| 192 | return self.ParseUntil(0)
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| 193 |
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| 194 |
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| 195 | # Must define these aliases AFTER Parser and Token are defined.
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| 196 | if TYPE_CHECKING:
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| 197 | NullFunc = Callable[[Parser, Token, int], arith_expr_t]
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| 198 | LeftFunc = Callable[[Parser, Token, arith_expr_t, int], arith_expr_t]
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| 199 |
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| 200 |
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