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# macroExpander.py
#
# Example pyparsing program for performing macro expansion, similar to
# the C pre-processor. This program is not as fully-featured, simply
# processing macros of the form:
# #def xxx yyyyy
# and replacing xxx with yyyyy in the rest of the input string. Macros
# can also be composed using other macros, such as
# #def zzz xxx+1
# Since xxx was previously defined as yyyyy, then zzz will be replaced
# with yyyyy+1.
#
# Copyright 2007 by Paul McGuire
#
from pyparsing import *
# define the structure of a macro definition (the empty term is used
# to advance to the next non-whitespace character)
identifier = Word(alphas + "_", alphanums + "_")
macroDef = "#def" + identifier("macro") + empty + restOfLine("value")
# define a placeholder for defined macros - initially nothing
macroExpr = Forward()
macroExpr << NoMatch()
# global dictionary for macro definitions
macros = {}
# parse action for macro definitions
def processMacroDefn(s, l, t):
macroVal = macroExpander.transformString(t.value)
macros[t.macro] = macroVal
macroExpr << MatchFirst(map(Keyword, macros.keys()))
return "#def " + t.macro + " " + macroVal
# parse action to replace macro references with their respective definition
def processMacroRef(s, l, t):
return macros[t[0]]
# attach parse actions to expressions
macroExpr.setParseAction(processMacroRef)
macroDef.setParseAction(processMacroDefn)
# define pattern for scanning through the input string
macroExpander = macroExpr | macroDef
# test macro substitution using transformString
testString = """
#def A 100
#def ALEN A+1
char Astring[ALEN];
char AA[A];
typedef char[ALEN] Acharbuf;
"""
print(macroExpander.transformString(testString))
print(macros)