Operators¶

The operators are special symbols that perform common mathematical operations. For example, operator + performs summation, and thus we can write $x +$y to denote the sum of variables $x and $y. There are over 20 different operators in YarnSpinner, which can be loosely grouped into the following categories:

Operator types¶

Arithmetic¶

The arithmetic operators, have the same meaning as in regular math. These apply to numeric arguments (with the exception of + which can also be used with strings):

operator

name

notes

+

-

subtraction

Also, a unary minus

*

multiplication

/

division

Division by 0 is not allowed, and will throw a runtime error if it occurs.

%

modulo

This operator can apply to both integer and decimal numbers, and it returns the remainder of integer division of two numbers. The right-hand side of % cannot be zero or a negative number, otherwise a runtime error will be thrown. The result of x % y is always a number in the range [0; y), regardless of the sign of x.

+

concatenation

When applied to strings, the + operator simply glues them together. For example, "Hello" + "World" produces string "HelloWorld".

Logical¶

The logical operators apply to boolean values. These operators can be written either in symbolic or word form – both forms are equivalent:

operator

name

notes

!, not

logical NOT

This is a unary operator that inverts its operand: !true is false, and !false is true.

&&, and

logical AND

Returns true if both of its arguments are true.

||, or

logical OR

Returns true if at least one of its arguments is true.

^, xor

logical XOR

Returns true if the arguments are different, and false if they are the same.

Assignment¶

The assignment operators modify the value of a variable. The left-hand side of such an operator is the variable that shall be modified, the right-hand side is the expression of the same type as the variable on the left:

operator

name

notes

=, to

assign

$var = X stores the value of X into the variable $var

+=

increase

$var += X is equivalent to $var = $var + X -= decrease $var -= X is equivalent to $var =$var - X

*=

multiply

$var *= X is equivalent to $var = $var * X /= divide $var /= X is equivalent to $var =$var / X

%=

reduce modulo

$var %= X is equivalent to $var = $var % X Unlike all other operators, the assignment operators do not produce a value. This means they cannot be used inside a larger expression, for example the following is invalid: 3 + ($x += 7). Instead, the assignment operators are only usable at the top level of commands such as <<set>>, <<declare>>, and <<local>>.

Relational¶

The relational operators compare various values. The first two operators in this list can be applied to operands of any types, as long as the types are the same. The remaining four operators can only be used with numbers. Regardless of the types of operands, the result of every relational operator is a boolean value, which can be either assigned to a variable, or used in a larger expression:

operator

name

notes

==

equality

!=

inequality

<

less than

<=

less than or equal

>

greater than

>=

greater than or equal

Note that operator chaining is not supported. Thus, for example, $x ==$y == $z will first compare variables $x and $y, then the result of that comparison, which is either true or false, will be compared with variable $z. Given that such expressions would be highly confusing to a reader, we recommend against using them. If you need to compare that all three values $x, $y and $z are the same, then you should use the && operator instead: $x == $y &&$x == \$z.

Precedence¶

Just as in mathematics, the operators have precedence ordering among them, meaning that some operators will always evaluate before the others. For example, if you write 3 + 4 * 5, then the result will be 23 instead of 35 because multiplication has higher precedence than addition and thus evaluates first.

The precedence order is as follows, from highest to lowest:

• *, /, %;

• -, +;

• ==, !=, <, <=, >=, >;

• !;

• &&, ^;

• ||;

• =, +=, -=, *=, /=, %=.

You can use parentheses () in order to alter the order of evaluation. For example, (3 + 4) * 5 is 35 instead of 23.