public object visit_Binary_Expr(GExpr.Binary expr)
{
Object left = evaluate(expr.left);
Object right = evaluate(expr.right);
switch (expr.Operator.type)
{
case tt.MINUS:
checkNumberOperands(expr.Operator, left, right);
return((double)left - (double)right);
case tt.SLASH:
checkNumberOperands(expr.Operator, left, right);
return((double)left / (double)right);
case tt.STAR:
checkNumberOperands(expr.Operator, left, right);
return((double)left * (double)right);
case tt.PLUS:
if ((left is double) && (right is double))
{
return((double)left + (double)right);
}
if ((left is string) && (right is string))
{
return(left.ToString() + right.ToString());
}
throw new RuntimeError(expr.Operator, "Operands must be two numbers or two strings");
case tt.GREATER:
checkNumberOperands(expr.Operator, left, right);
return((double)left > (double)right);
case tt.GREATER_EQUAL:
checkNumberOperands(expr.Operator, left, right);
return((double)left >= (double)right);
case tt.LESS:
checkNumberOperands(expr.Operator, left, right);
return((double)left < (double)right);
case tt.LESS_EQUAL:
checkNumberOperands(expr.Operator, left, right);
return((double)left <= (double)right);
case tt.EQUAL_EQUAL:
return(isEqual(left, right));
case tt.BANG_EQUAL:
return(!isEqual(left, right));
}
return(null);
}
private GExpr.Expr equality()
{
GExpr.Expr expr = comparison();
while (Match(tt.BANG_EQUAL, tt.EQUAL_EQUAL))
{
Token Operator = previous();
GExpr.Expr right = comparison();
expr = new GExpr.Binary(expr, Operator, right);
}
return(expr);
}
private GExpr.Expr multiplication()
{
GExpr.Expr expr = unary();
while (Match(tt.SLASH, tt.STAR))
{
Token Operator = previous();
GExpr.Expr right = unary();
expr = new GExpr.Binary(expr, Operator, right);
}
return(expr);
}
private GExpr.Expr addition()
{
GExpr.Expr expr = multiplication();
while (Match(tt.MINUS, tt.PLUS))
{
Token Operator = previous();
GExpr.Expr right = multiplication();
expr = new GExpr.Binary(expr, Operator, right);
}
return(expr);
}
private GExpr.Expr comparison()
{
GExpr.Expr expr = addition();
while (Match(tt.GREATER, tt.GREATER_EQUAL, tt.LESS, tt.LESS_EQUAL))
{
Token Operator = previous();
GExpr.Expr right = addition();
expr = new GExpr.Binary(expr, Operator, right);
}
return(expr);
}
