1 files changed, 33 insertions, 22 deletions

diff --git a/examples/include_preprocessor.py b/examples/include_preprocessor.py
index dbb333b..0b0d742 100644
--- a/examples/include_preprocessor.py
+++ b/examples/include_preprocessor.py
@@ -8,31 +8,36 @@
 import pyparsing as pp
 from pathlib import Path
 
+# parser elements to be used to assemble into #include parser
 SEMI = pp.Suppress(';')
 INCLUDE = pp.Keyword("#include")
 quoted_string = pp.quotedString.addParseAction(pp.removeQuotes)
+file_ref = (quoted_string
+            | pp.Word(pp.printables, excludeChars=';'))
 
-include_directive = (INCLUDE
-                     + (quoted_string
-                        | pp.Word(pp.printables, excludeChars=';'))("include_file")
-                     + SEMI)
+# parser for parsing "#include xyz.dat;" directives
+include_directive = (INCLUDE + file_ref("include_file_name") + SEMI)
 
-# add parse action that will recursively pull in included files
+# add parse action that will recursively pull in included files - when
+# using transformString, the value returned from the parse action will replace
+# the text matched by the attached expression
 seen = set()
 def read_include_contents(s, l, t):
-    include_file_ref = t.include_file
+    include_file_ref = t.include_file_name
     include_echo = "/* {} */".format(pp.line(l, s).strip())
 
     # guard against recursive includes
     if include_file_ref not in seen:
         seen.add(include_file_ref)
+        included_file_contents = Path(include_file_ref).read_text()
         return (include_echo + '\n'
-                + include_directive.transformString(Path(include_file_ref).read_text()))
+                + include_directive.transformString(included_file_contents))
     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
+# attach include processing method as parse action (parse-time callback)
+# to include_directive expression
 include_directive.addParseAction(read_include_contents)
 
 
@@ -40,24 +45,29 @@ if __name__ == '__main__':
 
     # demo
 
-    # create test files
+    # create test files:
+    # - a.txt includes b.txt
+    # - b.txt includes c.txt
+    # - c.txt includes b.txt (must catch infinite recursion)
     Path('a.txt').write_text("""\
-    /* a.txt */
-    int i;
+        /* a.txt */
+        int i;
     
-    #include b.txt;
-    """)
+        /* sometimes included files aren't in quotes */    
+        #include b.txt;
+        """)
 
     Path('b.txt').write_text("""\
-    i = 100;
-    #include 'c.txt';
-    """)
+        i = 100;
+        #include 'c.txt';
+        """)
 
     Path('c.txt').write_text("""\
-    i += 1;
-    
-    #include b.txt;
-    """)
+        i += 1;
+        
+        /* watch out! this might be recursive if this file included by b.txt */
+        #include b.txt;
+        """)
 
 
     # use include_directive.transformString to perform includes
@@ -69,8 +79,9 @@ if __name__ == '__main__':
     print(initial_file)
     print('-----------------')
 
-    # print expanded file
-    print(include_directive.transformString(initial_file))
+    # expand includes in source file (and any included files) and print the result
+    expanded_source = include_directive.transformString(initial_file)
+    print(expanded_source)
 
     # clean up
     for fname in "a.txt b.txt c.txt".split():