private Expr term()
{
Expr expr = factor();
while (match(TokenType.PLUS, TokenType.MINUS))
{
Token op = previous();
Expr right = factor();
expr = new Expr.Binary(expr, op, right);
}
return(expr);
}
private Expr comparison()
{
Expr expr = term();
while (match(TokenType.GREATER, TokenType.GREATER_EQUAL, TokenType.LESS, TokenType.LESS_EQUAL))
{
Token op = previous();
Expr right = term();
expr = new Expr.Binary(expr, op, right);
}
return(expr);
}
private Expr equality()
{
Expr expr = comparison();
while (match(TokenType.EXCLAM_EQUAL, TokenType.EQUAL_EQUAL))
{
Token op = previous();
Expr right = comparison();
expr = new Expr.Binary(expr, op, right);
}
return(expr);
}
public string visitBinaryExpr(Expr.Binary expr)
{
return(paranthesize(expr.op.lexeme, expr.left, expr.right));
}
public object visitBinaryExpr(Expr.Binary expr)
{
object left = evaluate(expr.left);
object right = evaluate(expr.right);
switch (expr.op.type)
{
case TokenType.SLASH:
checkNumberOperand(expr.op, left, right);
if ((double)right == 0)
{
throw new RuntimeError(expr.op, "Division by 0 not permitted!");
}
return((double)left / (double)right);
case TokenType.MINUS:
checkNumberOperand(expr.op, left, right);
return((double)left - (double)right);
case TokenType.STAR:
checkNumberOperand(expr.op, left, right);
return((double)left * (double)right);
case TokenType.PLUS:
if (left is double && right is double)
{
return((double)left + (double)right);
}
if (left is string && right is string)
{
return((string)left + (string)right);
}
throw new RuntimeError(expr.op, "Operands must be 2 numbers or 2 strings!");
case TokenType.GREATER:
checkNumberOperand(expr.op, left, right);
return((double)left > (double)right);
case TokenType.GREATER_EQUAL:
checkNumberOperand(expr.op, left, right);
return((double)left >= (double)right);
case TokenType.LESS:
checkNumberOperand(expr.op, left, right);
return((double)left < (double)right);
case TokenType.LESS_EQUAL:
checkNumberOperand(expr.op, left, right);
return((double)left <= (double)right);
case TokenType.EQUAL_EQUAL:
return(isEqual(left, right));
case TokenType.EXCLAM_EQUAL:
return(!isEqual(left, right));
}
return(null);
}
