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    <p>1) Change <code>Literal("if")</code> to <code>Keyword("if")</code> (and so on, down to <code>Literal("void")</code>), to prevent matching the leading "if" of a variable named <code>"ifactor"</code>.</p> <p>2) <code>nums</code>, <code>alphas</code>, and <code>alphanums</code> are not expressions, they are strings, that can be used with the Word class to define some typical sets of characters when defining "words" like "a number is a word made up of nums", or "an identifier is a word that starts with an alpha, followed by zero or more alphanums." So instead of: </p> <pre><code>number = nums identifier = alphas + OneOrMore(alphanums) </code></pre> <p>you want</p> <pre><code>number = Word(nums) identifier = Word(alphas, alphanums) </code></pre> <p>3) Instead of <code>Combine</code>, I think you want <code>Group</code>. Use <code>Combine</code> when you want the matched tokens to be contiguous with no intervening whitespace, and will concatenate the tokens and return them as a single string. <code>Combine</code> is often used in cases like this:</p> <pre><code>realnum = Combine(Word(nums) + "." + Word(nums)) </code></pre> <p>Without <code>Combine</code>, parsing <code>"3.14"</code> would return the list of strings <code>['3', '.', '14']</code>, so we add <code>Combine</code> so that the parsed result for realnum is <code>'3.14'</code> (which you could then pass to a parse action to convert to the actual floating value <code>3.14</code>). <code>Combine</code>s enforcement of no intervening whitespace also keeps us from accidentally parsing <code>'The answer is 3. 10 is too much.'</code> and thinking the <code>"3. 10"</code> represents a real number.</p> <p>4) This should not cause your error, but your input string has <em>lots</em> of extra spaces. If you get your grammar working, you should be able to parse <code>"int x;"</code> just as well as <code>"int x ;"</code>.</p> <p>Hope some of these hints get you going. Have you read any online pyparsing articles or tutorials? And please look through the online examples. You'll need to get a good grasp of how <code>Word</code>, <code>Literal</code>, <code>Combine</code>, etc. perform their individual parsing tasks.</p> <p>5) You have mis-implemented the recursive definitions for term and statement. Instead of assigning <code>''</code> to them, write:</p> <pre><code>term = Forward() statement = Forward() </code></pre> <p>Then when you go to actually define them with their recursive definitions, use the <code>&lt;&lt;</code> operator (and be sure to enclose the RHS in <code>()</code>'s).</p> <pre><code>term &lt;&lt; (... term definition ...) statement &lt;&lt; (... statement definition ...) </code></pre> <p>You can find an example of a recursive parser <a href="http://www.ptmcg.com/geo/python/confs/examples/list1.py.txt" rel="noreferrer">here</a>, and a presentation on basic pyparsing usage <a href="http://www.ptmcg.com/geo/python/confs/TxUnconf2008Pyparsing.html" rel="noreferrer">here</a> - see the section titled "Parsing Lists" for more step-by-step on how the recursion is handled.</p>
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    1. COThanks Paul. I've replaced all instances of Combine with Group and now I'm getting some different errors which I think are related to how my rules are written rather than the syntax I've used. I've updated my original post to reflect those changes you suggested and the new error I have.
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    2. COExcellent Paul, thanks very much. I wish I could +1 you more :)
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