//term ::= <int-const> | <str-const> | <keyword-const> | <var-name> |
// <var-name> '[' <expression> ']' | <sub-call> | '(' expression ')' |
// ('-' | '!') <term>
private void ParseTerm()
{
if (LookAheadToken.Type == TokenType.IntConst)
{
Token intConst = NextToken();
_codeGenerator.IntConst(int.Parse(intConst.Value));
}
else if (LookAheadToken.Type == TokenType.StrConst)
{
Token strConst = NextToken();
_codeGenerator.StrConst(strConst.Value);
}
else if (IsNextTokenKeywordConst())
{
Token keywordConst = NextToken();
switch (keywordConst.Value)
{
case "true":
_codeGenerator.True();
break;
case "false":
_codeGenerator.False();
break;
case "null":
_codeGenerator.Null();
break;
case "this":
if (_currentSub.Kind != SubroutineKind.Method &&
_currentSub.Kind != SubroutineKind.Constructor)
{
ThrowCompilationException("'this' can be used only in a method or a constructor");
}
_codeGenerator.This();
break;
default:
ThrowCompilationException("Unexpected keyword constant '" + keywordConst.Value + "'");
break;
}
}
else if (LookAheadToken.Type == TokenType.Ident)
{
//This is either a variable name, an array access, or a
//subroutine call. To know which it's going to be, we need
//the token after the variable name.
Token varName = NextToken();
if (LookAheadToken.Value == ".")
{
ParseSubCall(varName);
}
else
{
//Now is the time to verify that we have a valid variable:
Symbol symbol = GetClosestSymbol(varName.Value);
if (symbol == null)
{
ThrowCompilationException("Undefined identifier '" + varName.Value + "'");
}
bool withArrayIndex = false;
if (LookAheadToken.Value == "[")
{
withArrayIndex = true;
VerifyArrayAccessAllowed(varName);
Match(new Token(TokenType.Symbol, "["));
ParseExpression();
Match(new Token(TokenType.Symbol, "]"));
}
_codeGenerator.VariableRead(varName, withArrayIndex);
}
}
else if (LookAheadToken.Value == "(")
{
Match(new Token(TokenType.Symbol, "("));
ParseExpression();
Match(new Token(TokenType.Symbol, ")"));
}
else if (IsNextTokenUnaryOp())
{
Token unaryOp = NextToken();
ParseTerm();
switch (unaryOp.Value)
{
case "-":
_codeGenerator.Negate();
break;
case "!":
_codeGenerator.Not();
break;
default:
ThrowCompilationException("Unexpected unary operator: " + unaryOp.Value);
break;
}
}
else
{
ThrowCompilationException("Expected a term, got: " + LookAheadToken.Value);
}
}