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PODebugging Pyparsing Grammar
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  1. PODebugging Pyparsing Grammar
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    copied!<p>I'm building a parser for an imaginary programming language called C-- (not the actual C-- language). I've gotten to the stage where I need to translate the language's grammar into something Pyparsing can accept. Unfortunatly when I come to parse my input string (which is correct and should not cause Pyparsing to error) it's not parsing correctly. I fear this is due to errors in my grammar, but as I'm starting Pyparsing for the first time, I can't seem to see where I'm going wrong.</p> <p>I've uploaded the grammar that I'm translating from <a href="http://www.box.net/shared/5a8lc7jz0p" rel="noreferrer">here</a> for people to have a read through.</p> <p><strong>EDIT:</strong> Updated with the advice from Paul.</p> <p>This is the grammer I've currently got (the two top lines of Syntax definition are terribly bad of me I know):</p> <pre><code># Lexical structure definition ifS = Keyword('if') elseS = Keyword('else') whileS = Keyword('while') returnS = Keyword('return') intVar = Keyword('int') voidKeyword = Keyword('void') sumdiff = Literal('+') | Literal('-') prodquot = Literal('*') | Literal('/') relation = Literal('&lt;=') | Literal('&lt;') | Literal('==') | \ Literal('!=') | Literal('&gt;') | Literal('=&gt;') lbrace = Literal('{') rbrace = Literal('}') lparn = Literal('(') rparn = Literal(')') semi = Literal(';') comma = Literal(',') number = Word(nums) identifier = Word(alphas, alphanums) # Syntax definition term = '' statement = '' variable = intVar + identifier + semi locals = ZeroOrMore(variable) expr = term | OneOrMore(Group(sumdiff + term)) args = ZeroOrMore(OneOrMore(Group(expr + comma)) | expr) funccall = Group(identifier + lparn + args + rparn) factor = Group(lparn + expr + rparn) | identifier | funccall | number term = factor | OneOrMore(prodquot + factor) cond = Group(lparn + expr + relation + expr + rparn) returnState = Group(returnS + semi) | Combine(returnS + expr + semi) assignment = Group(identifier + '=' + expr + semi) proccall = Group(identifier + lparn + args + rparn + semi) block = Group(lbrace + locals + statement + rbrace) iteration = Group(whileS + cond + block) selection = Group(ifS + cond + block) | Group(ifS + cond + block + elseS + block) statement = OneOrMore(proccall | assignment | selection | iteration | returnState) param = Group(intVar + identifier) paramlist = OneOrMore(Combine(param + comma)) | param params = paramlist | voidKeyword procedure = Group(voidKeyword + identifier + lparn + params + rparn + block) function = Group(intVar + identifier + lparn + params + rparn + block) declaration = variable | function | procedure program = OneOrMore(declaration) </code></pre> <p>I'd like to know if there are any mistakes I've made in translating the grammar across and what improvements I could do to make it simplified whilst adhering to the grammar I've been given.</p> <p><strong>EDIT 2:</strong> Updated to include the new error.</p> <p>Here is the input string I am parsing:</p> <pre><code>int larger ( int first , int second ) { if ( first &gt; second ) { return first ; } else { return second ; } } void main ( void ) { int count ; int sum ; int max ; int x ; x = input ( ) ; max = x ; sum = 0 ; count = 0 ; while ( x != 0 ) { count = count + 1 ; sum = sum + x ; max = larger ( max , x ) ; x = input ( ) ; } output ( count ) ; output ( sum ) ; output ( max ) ; } </code></pre> <p>And this is the error message I get when running my program from Terminal:</p> <pre><code>/Users/Joe/Documents/Eclipse Projects/Parser/src/pyparsing.py:1156: SyntaxWarning: null string passed to Literal; use Empty() instead other = Literal( other ) /Users/Joe/Documents/Eclipse Projects/Parser/src/pyparsing.py:1258: SyntaxWarning: null string passed to Literal; use Empty() instead other = Literal( other ) Expected ")" (at char 30), (line:6, col:26) None </code></pre>
 

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