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# parser.py - simple top-down operator precedence parser for mercurial
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#
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# Copyright 2010 Matt Mackall <mpm@selenic.com>
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#
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# This software may be used and distributed according to the terms of the
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# GNU General Public License version 2 or any later version.
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# see http://effbot.org/zone/simple-top-down-parsing.htm and
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# http://eli.thegreenplace.net/2010/01/02/top-down-operator-precedence-parsing/
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# for background
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# takes a tokenizer and elements
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# tokenizer is an iterator that returns (type, value, pos) tuples
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# elements is a mapping of types to binding strength, prefix, infix and
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# optional suffix actions
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# an action is a tree node name, a tree label, and an optional match
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# __call__(program) parses program into a labeled tree
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import error
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from i18n import _
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class parser(object):
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def __init__(self, elements, methods=None):
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self._elements = elements
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self._methods = methods
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self.current = None
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def _advance(self):
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'advance the tokenizer'
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t = self.current
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self.current = next(self._iter, None)
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return t
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def _match(self, m, pos):
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'make sure the tokenizer matches an end condition'
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if self.current[0] != m:
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raise error.ParseError(_("unexpected token: %s") % self.current[0],
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self.current[2])
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self._advance()
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def _parse(self, bind=0):
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token, value, pos = self._advance()
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# handle prefix rules on current token
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prefix = self._elements[token][1]
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if not prefix:
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raise error.ParseError(_("not a prefix: %s") % token, pos)
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if len(prefix) == 1:
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expr = (prefix[0], value)
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else:
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if len(prefix) > 2 and prefix[2] == self.current[0]:
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self._match(prefix[2], pos)
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expr = (prefix[0], None)
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else:
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expr = (prefix[0], self._parse(prefix[1]))
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if len(prefix) > 2:
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self._match(prefix[2], pos)
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# gather tokens until we meet a lower binding strength
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while bind < self._elements[self.current[0]][0]:
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token, value, pos = self._advance()
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e = self._elements[token]
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# check for suffix - next token isn't a valid prefix
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if len(e) == 4 and not self._elements[self.current[0]][1]:
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suffix = e[3]
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expr = (suffix[0], expr)
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else:
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# handle infix rules
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if len(e) < 3 or not e[2]:
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raise error.ParseError(_("not an infix: %s") % token, pos)
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infix = e[2]
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if len(infix) == 3 and infix[2] == self.current[0]:
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self._match(infix[2], pos)
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expr = (infix[0], expr, (None))
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else:
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expr = (infix[0], expr, self._parse(infix[1]))
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if len(infix) == 3:
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self._match(infix[2], pos)
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return expr
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def parse(self, tokeniter):
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'generate a parse tree from tokens'
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self._iter = tokeniter
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self._advance()
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res = self._parse()
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token, value, pos = self.current
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return res, pos
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def eval(self, tree):
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'recursively evaluate a parse tree using node methods'
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if not isinstance(tree, tuple):
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return tree
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return self._methods[tree[0]](*[self.eval(t) for t in tree[1:]])
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def __call__(self, tokeniter):
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'parse tokens into a parse tree and evaluate if methods given'
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t = self.parse(tokeniter)
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if self._methods:
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return self.eval(t)
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return t
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def buildargsdict(trees, funcname, keys, keyvaluenode, keynode):
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"""Build dict from list containing positional and keyword arguments
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Invalid keywords or too many positional arguments are rejected, but
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missing arguments are just omitted.
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"""
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if len(trees) > len(keys):
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raise error.ParseError(_("%(func)s takes at most %(nargs)d arguments")
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% {'func': funcname, 'nargs': len(keys)})
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args = {}
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# consume positional arguments
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for k, x in zip(keys, trees):
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if x[0] == keyvaluenode:
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break
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args[k] = x
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# remainder should be keyword arguments
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for x in trees[len(args):]:
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if x[0] != keyvaluenode or x[1][0] != keynode:
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raise error.ParseError(_("%(func)s got an invalid argument")
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% {'func': funcname})
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k = x[1][1]
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if k not in keys:
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raise error.ParseError(_("%(func)s got an unexpected keyword "
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"argument '%(key)s'")
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% {'func': funcname, 'key': k})
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if k in args:
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raise error.ParseError(_("%(func)s got multiple values for keyword "
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"argument '%(key)s'")
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% {'func': funcname, 'key': k})
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args[k] = x[2]
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return args
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def _prettyformat(tree, leafnodes, level, lines):
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if not isinstance(tree, tuple) or tree[0] in leafnodes:
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lines.append((level, str(tree)))
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else:
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lines.append((level, '(%s' % tree[0]))
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for s in tree[1:]:
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_prettyformat(s, leafnodes, level + 1, lines)
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lines[-1:] = [(lines[-1][0], lines[-1][1] + ')')]
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def prettyformat(tree, leafnodes):
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lines = []
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_prettyformat(tree, leafnodes, 0, lines)
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output = '\n'.join((' ' * l + s) for l, s in lines)
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return output
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def simplifyinfixops(tree, targetnodes):
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"""Flatten chained infix operations to reduce usage of Python stack
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>>> def f(tree):
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... print prettyformat(simplifyinfixops(tree, ('or',)), ('symbol',))
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>>> f(('or',
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... ('or',
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... ('symbol', '1'),
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... ('symbol', '2')),
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... ('symbol', '3')))
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(or
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('symbol', '1')
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('symbol', '2')
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('symbol', '3'))
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>>> f(('func',
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... ('symbol', 'p1'),
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... ('or',
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... ('or',
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... ('func',
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... ('symbol', 'sort'),
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... ('list',
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... ('or',
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... ('or',
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... ('symbol', '1'),
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... ('symbol', '2')),
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... ('symbol', '3')),
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... ('negate',
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... ('symbol', 'rev')))),
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... ('and',
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... ('symbol', '4'),
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... ('group',
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... ('or',
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... ('or',
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... ('symbol', '5'),
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... ('symbol', '6')),
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... ('symbol', '7'))))),
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... ('symbol', '8'))))
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(func
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('symbol', 'p1')
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(or
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(func
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('symbol', 'sort')
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(list
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(or
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('symbol', '1')
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('symbol', '2')
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('symbol', '3'))
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(negate
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('symbol', 'rev'))))
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(and
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('symbol', '4')
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(group
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(or
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('symbol', '5')
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('symbol', '6')
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('symbol', '7'))))
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('symbol', '8')))
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"""
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if not isinstance(tree, tuple):
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return tree
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op = tree[0]
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if op not in targetnodes:
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return (op,) + tuple(simplifyinfixops(x, targetnodes) for x in tree[1:])
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# walk down left nodes taking each right node. no recursion to left nodes
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# because infix operators are left-associative, i.e. left tree is deep.
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# e.g. '1 + 2 + 3' -> (+ (+ 1 2) 3) -> (+ 1 2 3)
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simplified = []
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x = tree
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while x[0] == op:
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l, r = x[1:]
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simplified.append(simplifyinfixops(r, targetnodes))
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x = l
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simplified.append(simplifyinfixops(x, targetnodes))
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simplified.append(op)
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return tuple(reversed(simplified))
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