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    <p>When looking at the BNF rules of an <code>if</code> statement:</p> <pre><code>ifthenelse ::= 'if' expr 'then' newline statement_list else_clause? 'endif' else_clause ::= 'else' newline statement_list | 'elseif' expr 'then' newline statement_list else_clause? </code></pre> <p>your translation:</p> <pre><code>if_statement : KEYWORD_IF expression KEYWORD_THEN statement_list else_clause? KEYWORD_ENDIF ; else_clause : KEYWORD_ELSEIF ((OPENPARENTHESIS expression CLOSEPARENTHESIS) | expression) KEYWORD_THEN statement_list | KEYWORD_ELSE ((OPENPARENTHESIS statement_list CLOSEPARENTHESIS) | statement_list) else_clause? ; </code></pre> <p>is incorrect (you have an optional <code>else_clause</code> in the <code>KEYWORD_ELSE</code> alternative).</p> <p>It should be:</p> <pre><code>if_statement : KEYWORD_IF expression KEYWORD_THEN statement_list else_clause? KEYWORD_ENDIF ; else_clause : KEYWORD_ELSE statement_list | KEYWORD_ELSEIF expression KEYWORD_THEN statement_list else_clause? ; </code></pre> <p>And not that you don't need <code>((OPENPARENTHESIS expression CLOSEPARENTHESIS) | expression)</code> since a <code>expression</code> already matches <code>'(' expression ')'</code>.</p> <p>But the observations above are not the cause of your problem(s). The real issue is that your grammar does not account for unary expressions. It does not match the <code>-1</code> in the expression <code>si__DroneSystem___data_V[this]!=-1</code>. </p> <p>Change your <code>expression</code> rule into this:</p> <pre><code>expression : OPENPARENTHESIS expression CLOSEPARENTHESIS | OPENBRACKET expression CLOSEBRACKET | func_call | array_ref | function_reference | const_statement | identifier | '+' expression | '-' expression | 'not' expression | expression ('*'|'/') expression | expression ('+'|'-') expression | expression ('&gt;'|'&lt;'|'=='|'!='|'&gt;='|'&lt;=') expression | expression ('and'|'or') expression | identifier ; </code></pre> <p>Now input like this:</p> <pre><code>if this==null then return elseif(si__DroneSystem___data_V[this]!=-1)then return endif </code></pre> <p>will be parsed as follows:</p> <p><img src="https://i.stack.imgur.com/KW7nC.png" alt="enter image description here"></p>
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    1. USBart Kiers
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    1. COThanks! It now parses that expression just fine. I'm still having trouble with FOURCCs though, which are integer constants defined by an opening and closing single quote, containing any combination of letters and digits. I've tried many logical ways to go about this, including `QUOTATION_SINGLE (LETTER|DIGIT)(LETTER|DIGIT)(LETTER|DIGIT)(LETTER|DIGIT) QUOTATION_SINGLE` but the parser still spits out the error `line 78:37 no viable alternative at input ''h01N''`. And just a side note: You have `const_statement` declared twice in `expression`.
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    2. COalso, possibly unrelated to FOURCCs, I'm getting `line 100:70 no viable alternative at input '==0andGetUnitTypeId(u)!='h01N''`... I'll have to fix FOURCC to be sure, but I think it might have something to do with skipping whitespaces. The script reads `set uu=CreateUnit(GetOwningPlayer(u),'h01N',x2,y2,0)` for line 78, and `if s!=null and GetUnitAbilityLevel(u,'Arav')==0 and GetUnitTypeId(u)!='h01N' then` for line 100.
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    3. CO@RectangleEquals, I don't see anything odd about your FOURCC rule, but there are many things in your grammar that don't comply with the BNF specs of JASS. I quickly hacked together a v4 compliant grammar that parses your 7500 LOC without any problem: https://gist.github.com/bkiers/5078351
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