parser: reorder infix/suffix handling to be similar to prefix/primary flow

It can be exactly the same flow as the prefix/primary handling. A suffix
action is accepted only if the next token never starts new term.

mercurial/parser.py

@@ -1,214 +1,213 b''
 # parser.py - simple top-down operator precedence parser for mercurial
 #
 # Copyright 2010 Matt Mackall <[e-mail]>
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 # see http://effbot.org/zone/simple-top-down-parsing.htm and
 # http://eli.thegreenplace.net/2010/01/02/top-down-operator-precedence-parsing/
 # for background
 
 # takes a tokenizer and elements
 # tokenizer is an iterator that returns (type, value, pos) tuples
 # elements is a mapping of types to binding strength, primary, prefix, infix
 # and suffix actions
 # an action is a tree node name, a tree label, and an optional match
 # __call__(program) parses program into a labeled tree
 
 import error
 from i18n import _
 
 class parser(object):
     def __init__(self, elements, methods=None):
         self._elements = elements
         self._methods = methods
         self.current = None
     def _advance(self):
         'advance the tokenizer'
         t = self.current
         self.current = next(self._iter, None)
         return t
     def _hasnewterm(self):
         'True if next token may start new term'
         return any(self._elements[self.current[0]][1:3])
     def _match(self, m):
         'make sure the tokenizer matches an end condition'
         if self.current[0] != m:
             raise error.ParseError(_("unexpected token: %s") % self.current[0],
                                    self.current[2])
         self._advance()
     def _parseoperand(self, bind, m=None):
         'gather right-hand-side operand until an end condition or binding met'
         if m and self.current[0] == m:
             expr = None
         else:
             expr = self._parse(bind)
         if m:
             self._match(m)
         return expr
     def _parse(self, bind=0):
         token, value, pos = self._advance()
         # handle prefix rules on current token, take as primary if unambiguous
         primary, prefix = self._elements[token][1:3]
         if primary and not (prefix and self._hasnewterm()):
             expr = (primary, value)
         elif prefix:
             expr = (prefix[0], self._parseoperand(*prefix[1:]))
         else:
             raise error.ParseError(_("not a prefix: %s") % token, pos)
         # gather tokens until we meet a lower binding strength
         while bind < self._elements[self.current[0]][0]:
             token, value, pos = self._advance()
+            # handle infix rules, take as suffix if unambiguous
             infix, suffix = self._elements[token][3:]
-            # check for suffix - next token isn't a valid prefix
             if suffix and not self._hasnewterm():
                 expr = (suffix[0], expr)
+            elif infix:
+                expr = (infix[0], expr, self._parseoperand(*infix[1:]))
             else:
-                # handle infix rules
-                if not infix:
-                    raise error.ParseError(_("not an infix: %s") % token, pos)
-                expr = (infix[0], expr, self._parseoperand(*infix[1:]))
+                raise error.ParseError(_("not an infix: %s") % token, pos)
         return expr
     def parse(self, tokeniter):
         'generate a parse tree from tokens'
         self._iter = tokeniter
         self._advance()
         res = self._parse()
         token, value, pos = self.current
         return res, pos
     def eval(self, tree):
         'recursively evaluate a parse tree using node methods'
         if not isinstance(tree, tuple):
             return tree
         return self._methods[tree[0]](*[self.eval(t) for t in tree[1:]])
     def __call__(self, tokeniter):
         'parse tokens into a parse tree and evaluate if methods given'
         t = self.parse(tokeniter)
         if self._methods:
             return self.eval(t)
         return t
 
 def buildargsdict(trees, funcname, keys, keyvaluenode, keynode):
     """Build dict from list containing positional and keyword arguments
 
     Invalid keywords or too many positional arguments are rejected, but
     missing arguments are just omitted.
     """
     if len(trees) > len(keys):
         raise error.ParseError(_("%(func)s takes at most %(nargs)d arguments")
                                % {'func': funcname, 'nargs': len(keys)})
     args = {}
     # consume positional arguments
     for k, x in zip(keys, trees):
         if x[0] == keyvaluenode:
             break
         args[k] = x
     # remainder should be keyword arguments
     for x in trees[len(args):]:
         if x[0] != keyvaluenode or x[1][0] != keynode:
             raise error.ParseError(_("%(func)s got an invalid argument")
                                    % {'func': funcname})
         k = x[1][1]
         if k not in keys:
             raise error.ParseError(_("%(func)s got an unexpected keyword "
                                      "argument '%(key)s'")
                                    % {'func': funcname, 'key': k})
         if k in args:
             raise error.ParseError(_("%(func)s got multiple values for keyword "
                                      "argument '%(key)s'")
                                    % {'func': funcname, 'key': k})
         args[k] = x[2]
     return args
 
 def _prettyformat(tree, leafnodes, level, lines):
     if not isinstance(tree, tuple) or tree[0] in leafnodes:
         lines.append((level, str(tree)))
     else:
         lines.append((level, '(%s' % tree[0]))
         for s in tree[1:]:
             _prettyformat(s, leafnodes, level + 1, lines)
         lines[-1:] = [(lines[-1][0], lines[-1][1] + ')')]
 
 def prettyformat(tree, leafnodes):
     lines = []
     _prettyformat(tree, leafnodes, 0, lines)
     output = '\n'.join(('  ' * l + s) for l, s in lines)
     return output
 
 def simplifyinfixops(tree, targetnodes):
     """Flatten chained infix operations to reduce usage of Python stack
 
     >>> def f(tree):
     ...     print prettyformat(simplifyinfixops(tree, ('or',)), ('symbol',))
     >>> f(('or',
     ...     ('or',
     ...       ('symbol', '1'),
     ...       ('symbol', '2')),
     ...     ('symbol', '3')))
     (or
       ('symbol', '1')
       ('symbol', '2')
       ('symbol', '3'))
     >>> f(('func',
     ...     ('symbol', 'p1'),
     ...     ('or',
     ...       ('or',
     ...         ('func',
     ...           ('symbol', 'sort'),
     ...           ('list',
     ...             ('or',
     ...               ('or',
     ...                 ('symbol', '1'),
     ...                 ('symbol', '2')),
     ...               ('symbol', '3')),
     ...             ('negate',
     ...               ('symbol', 'rev')))),
     ...         ('and',
     ...           ('symbol', '4'),
     ...           ('group',
     ...             ('or',
     ...               ('or',
     ...                 ('symbol', '5'),
     ...                 ('symbol', '6')),
     ...               ('symbol', '7'))))),
     ...       ('symbol', '8'))))
     (func
       ('symbol', 'p1')
       (or
         (func
           ('symbol', 'sort')
           (list
             (or
               ('symbol', '1')
               ('symbol', '2')
               ('symbol', '3'))
             (negate
               ('symbol', 'rev'))))
         (and
           ('symbol', '4')
           (group
             (or
               ('symbol', '5')
               ('symbol', '6')
               ('symbol', '7'))))
         ('symbol', '8')))
     """
     if not isinstance(tree, tuple):
         return tree
     op = tree[0]
     if op not in targetnodes:
         return (op,) + tuple(simplifyinfixops(x, targetnodes) for x in tree[1:])
 
     # walk down left nodes taking each right node. no recursion to left nodes
     # because infix operators are left-associative, i.e. left tree is deep.
     # e.g. '1 + 2 + 3' -> (+ (+ 1 2) 3) -> (+ 1 2 3)
     simplified = []
     x = tree
     while x[0] == op:
         l, r = x[1:]
         simplified.append(simplifyinfixops(r, targetnodes))
         x = l
     simplified.append(simplifyinfixops(x, targetnodes))
     simplified.append(op)
     return tuple(reversed(simplified))