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     object --+        
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  ParserElement --+    
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ParseElementEnhance --+
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                     Forward
Forward declaration of an expression to be defined later - used for 
  recursive grammars, such as algebraic infix notation. When the expression
  is known, it is assigned to the Forward variable using the 
  '<<' operator.
Note: take care when assigning to Forward not to overlook
  precedence of operators. Specifically, '|' has a lower precedence than 
  '<<', so that:
fwdExpr << a | b | c
will actually be evaluated as:
(fwdExpr << a) | b | c
thereby leaving b and c out as parseable alternatives.  It is 
  recommended that you explicitly group the values inserted into the 
  Forward:
fwdExpr << (a | b | c)
Converting to use the '<<=' operator instead will avoid this problem.
See ParseResults.pprint for an example of a recursive parser
  created using Forward.
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| Method Details | 
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 x.__init__(...) initializes x; see help(type(x)) for signature 
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 Disables the skipping of whitespace before matching the characters in 
  the  
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 Check defined expressions for valid structure, check for infinite recursive definitions. 
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 str(x) 
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 Make a copy of this  Example: 
   integer = Word(nums).setParseAction(lambda toks: int(toks[0]))
   integerK = integer.copy().addParseAction(lambda toks: toks[0]*1024) + Suppress("K")
   integerM = integer.copy().addParseAction(lambda toks: toks[0]*1024*1024) + Suppress("M")
   
   print(OneOrMore(integerK | integerM | integer).parseString("5K 100 640K 256M"))
prints: [5120, 100, 655360, 268435456] Equivalent form of  
   integerM = integer().addParseAction(lambda toks: toks[0]*1024*1024) + Suppress("M")
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