Add example include_preprocessor.py

1 files changed, 77 insertions, 0 deletions

diff --git a/examples/include_preprocessor.py b/examples/include_preprocessor.py
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+++ b/examples/include_preprocessor.py
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+#
+# include_preprocessor.py
+#
+# Short pyparsing script to perform #include inclusions similar to the C preprocessor
+#
+# Copyright 2019, Paul McGuire
+#
+import pyparsing as pp
+from pathlib import Path
+
+SEMI = pp.Suppress(';')
+INCLUDE = pp.Keyword("#include")
+quoted_string = pp.quotedString.addParseAction(pp.removeQuotes)
+
+include_directive = (INCLUDE
+                     + (quoted_string
+                        | pp.Word(pp.printables, excludeChars=';'))("include_file")
+                     + SEMI)
+
+# add parse action that will recursively pull in included files
+seen = set()
+def read_include_contents(s, l, t):
+    include_file_ref = t.include_file
+    include_echo = "/* {} */".format(pp.line(l, s).strip())
+
+    # guard against recursive includes
+    if include_file_ref not in seen:
+        seen.add(include_file_ref)
+        return (include_echo + '\n'
+                + include_directive.transformString(Path(include_file_ref).read_text()))
+    else:
+        lead = ' '*(pp.col(l, s) - 1)
+        return "/* recursive include! */\n{}{}".format(lead, include_echo)
+
+# attach include processing method as parse action to include_directive expression
+include_directive.addParseAction(read_include_contents)
+
+
+if __name__ == '__main__':
+
+    # demo
+
+    # create test files
+    Path('a.txt').write_text("""\
+    /* a.txt */
+    int i;
+    
+    #include b.txt;
+    """)
+
+    Path('b.txt').write_text("""\
+    i = 100;
+    #include 'c.txt';
+    """)
+
+    Path('c.txt').write_text("""\
+    i += 1;
+    
+    #include b.txt;
+    """)
+
+
+    # use include_directive.transformString to perform includes
+
+    # read contents of original file
+    initial_file = Path('a.txt').read_text()
+
+    # print original file
+    print(initial_file)
+    print('-----------------')
+
+    # print expanded file
+    print(include_directive.transformString(initial_file))
+
+    # clean up
+    for fname in "a.txt b.txt c.txt".split():
+        Path(fname).unlink()