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# macro_expander.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, 2023 by Paul McGuire
#
import pyparsing as pp
# define the structure of a macro definition (the empty term is used
# to advance to the next non-whitespace character)
identifier = pp.common.identifier
macro_def = "#def" + identifier("macro") + pp.empty + pp.restOfLine("value")
# define a placeholder for defined macros - initially nothing
macro_expr = pp.Forward()
macro_expr << pp.NoMatch()
# global dictionary for macro definitions
macros = {}
# parse action for macro definitions
def process_macro_defn(t):
macro_val = macro_expander.transform_string(t.value)
macros[t.macro] = macro_val
macro_expr << pp.MatchFirst(map(pp.Keyword, macros))
return f"#def {t.macro} {macro_val}"
# parse action to replace macro references with their respective definition
def process_macro_ref(t):
return macros[t[0]]
# attach parse actions to expressions
macro_expr.set_parse_action(process_macro_ref)
macro_def.set_parse_action(process_macro_defn)
# define pattern for scanning through the input string
macro_expander = macro_expr | macro_def
# test macro substitution using transformString
test_string = """
#def A 100
#def ALEN A+1
char Astring[ALEN];
char AA[A];
typedef char[ALEN] Acharbuf;
"""
print(test_string)
print("-" * 40)
print(macro_expander.transform_string(test_string))
print(macros)