Debugging Pyparsing Grammar

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.

I've uploaded the grammar that I'm translating from here for people to have a read through.

EDIT: Updated with the advice from Paul.

This is the grammer I've currently got (the two top lines of Syntax definition are terribly bad of me I know):

# 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('<=') | Literal('<') | Literal('==') | \
           Literal('!=') | Literal('>') | Literal('=>')
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)

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.

EDIT 2: Updated to include the new error.

Here is the input string I am parsing:

int larger ( int first , int second ) { 
if ( first > 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 ) ; 
} 

And this is the error message I get when running my program from Terminal:

/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