Operators

Arithmetic

/ never truncates. 7 / 2 is 3.5 even though both operands look like integers, because there is only one numeric type. When you want the integer, ask for it with //.

// rounds towards negative infinity, while % keeps the sign of the left operand:

echo -7 // 2
echo 7 // -2
echo -7 % 3
echo 7 % -3

-4
-4
-1
1

% works on non-integers too: 7.5 % 2 is 1.5.

Comparison

== compares by value for numbers, strings, lists and dictionaries, and by identity for everything else. A class changes that for its instances with @eq.

echo 1 == 1.0
echo [1, 2] == [1, 2]
echo {a: 1} == {a: 1}
echo '1' == 1

true
true
true
false

There is no coercion in ==. A string is never equal to a number.

The ordering operators are for numbers. Comparing two strings with < raises a TypeError; use compare(), which returns -1, 0 or 1:

echo 'abc'.compare('abd')

-1

Logic

Zuri spells these as words:

and and or short-circuit, and they return the operand, not a boolean:

echo 1 and 2
echo nil or 'fallback'

2
fallback

That is what makes var name = given or 'anonymous' work. Remember that 0, NaN, '' and false are falsy, so this idiom is only safe when those are not legitimate values.

The Conditional Operator

echo true ? 'yes' : 'no'

yes

cond ? a : b evaluates cond, then exactly one of the branches.

Bitwise

echo ~5
echo 5 >>> 1
echo 1 << 10

-6
2
1024

Bitwise operators work on the integer value of a number, and on bigints.

Concatenation and Repetition

+ on a string concatenates, and a number on either side is converted:

echo 'n=' + 5

n=5

+ on a list concatenates; * repeats:

echo [1, 2] + [3]
echo [1, 2] * 2

[1, 2, 3]
[1, 2, 1, 2]

Dictionaries do not support +. Use extend().

Anything the language does not define raises a TypeError that names the exact signature:

catch {
  echo nil + 1
} as e {
  echo e.message
}

operator '+' not defined for call signature (nil, number)

Classes can define what + and every other operator mean for their own instances. That is Chapter 6.

Member, Index and Slice

Negative indices count back from the end, for both strings and lists.

Precedence

From tightest to loosest. Everything on one row binds equally and associates left to right, except **, which associates right to left.

** follows the mathematical convention. It binds tighter than multiplication and tighter than a unary operator written before it, and it groups from the right:

echo 2 * 3 ** 2
echo 2 ** 3 ** 2
echo -2 ** 2
echo 2 ** -1

18
512
-4
0.5

2 * 3 ** 2 is 2 * (3 ** 2), 2 ** 3 ** 2 is 2 ** (3 ** 2), and -2 ** 2 is -(2 ** 2). The exponent itself may carry a sign, so 2 ** -1 needs no parentheses. Write (-2) ** 2 to raise a negative number.

.. binds very tightly, to primaries only. 1 + 2..5 parses as 1 + (2..5). Parenthesise any range whose endpoints are expressions.

Operators Zuri Does Not Have

There is no in operator for membership; use contains(). There is no ?. optional chaining and no ?? null coalescing; or covers the common case. There is no comma operator, and no += on a member that does not already exist.