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package ch.bfh.parser;
import ch.bfh.lexer.CalculatorLexer;
import ch.bfh.lexer.Token;
class FactorParser extends Parser {
ExpressionParser expression; // only used when parenthesis are found
boolean isNegative = false;
boolean somethingWasParsed = false;
public FactorParser(CalculatorLexer cl, Token lastToken) {
this.cl = cl;
this.lastToken = lastToken;
parse();
}
@Override
protected void parse() {
Token token = lastToken;
lastToken = null;
loop:
while (token != null && token.type != Token.EOL) {
switch (token.type) {
case Token.MUL:
case Token.DIV:
case Token.ADD:
if (somethingWasParsed) { // finished parsing the Factor
lastToken = token; // sending the token to the parent
break loop;
} else
throw new ParserException("Empty expression before '" + token.str + "'.");
case Token.SUB:
if (!somethingWasParsed)
if (!isNegative)
isNegative = true;
else
throw new ParserException("A factor cannot contain two '-'.");
else { // Meaning we could have parsed '-4' or '4' and '-' is the next digit which is op for the overall expression
lastToken = token;
break loop;
}
break;
case Token.NUM:
if (!somethingWasParsed) {
value = token.value;
somethingWasParsed = true;
} else
throw new ParserException("Missing operator between the two Factors.");
break;
case Token.ID:
if (!somethingWasParsed) {
expression = variables.get(token.str);
if (expression == null)
throw new ParserException("'"+token.str+"' is not yet defined.");
somethingWasParsed = true;
} else
throw new ParserException("Missing operator between the two Factors.");
break;
case Token.PAL:
if (!somethingWasParsed) {
expression = new ExpressionParser(cl, token, true);
if (expression.lastToken.type != Token.PAR)
throw new ParserException("No matching closing parenthesis were found.");
somethingWasParsed = true;
} else
throw new ParserException("Missing operator between the two Factors.");
break;
case Token.PAR: // Going as high as possible --> possibly the end of an expression created by a Factor :)
if (somethingWasParsed)
lastToken = token;
else throw new ParserException("Missing expression before closing the parenthesis.");
break loop;
case Token.EQU:
case Token.LET:
throw new ParserException("The inputted token '"+token.str+"' can only be placed in a variable declaration context (let var = Expression).");
case Token.END:
throw new ParserException("The keyword 'exit' can only be placed at the beginning of an expression.");
}
token = cl.nextToken();
}
}
@Override
public double getValue() {
if (expression != null)
if (isNegative)
return expression.getValue() * (-1);
else
return expression.getValue();
if (isNegative)
return value * (-1);
return value;
}
}
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