Operators

The earlier pages introduced operators as they came up. This page gathers them in one place, so it is also a page to come back to.

Arithmetic

Operator	Meaning	Example	Result
+	add	7 + 2	9
-	subtract	7 - 2	5
*	multiply	7 * 2	14
/	divide, always giving a Float	7 / 2	3.5
//	divide and round down	7 // 2	3
%	the remainder after //	7 % 2	1
**	raise to a power	2 ** 10	1024
- (in front)	negate	-(3 + 4)	-7

+ also joins two strings. Numbers explains division, mixing Int and Float, and what happens on overflow.

Comparison

Operator	Meaning	Example	Result
==	equal	3 == 3	true
!=	not equal	3 != 4	true
< <=	less than, or equal	3 < 5	true
> >=	greater than, or equal	5 >= 5	true

Comparisons can be chained: 0 <= score <= 100 asks whether score is in that range. See Booleans and Comparison.

Logic

Operator	Meaning	Example	Result
and	both are true	true and false	false
or	at least one is true	true or false	true
not	the opposite	not true	false

and and or stop as soon as the answer is known.

Assignment

Assignment is a statement of its own, never part of an expression, so it can’t be confused with == inside a condition.

Operator	Meaning	Same as
=	give a new value
+=	add to	x = x + y
-=	subtract from	x = x - y
*=	multiply by	x = x * y
/=	divide by	x = x / y
//=	divide and round down	x = x // y

var seconds = 200
seconds //= 60
print(seconds)

Output

3

Other operators

These belong to ideas that later pages explain; they are listed here so the table is complete.

Operator	Meaning	Explained in
a..b, a..<b	a range from a through b, or up to but not including b	Ranges and Slicing
x is Type	whether a value is of a type	Optionals, Inheritance
thing.name	a member of a value, such as a method or property	Text, Structs
thing?.name	a member, if the value is there	Optionals
f(x)	call a function	Functions
list[i]	an item by position	Lists
if c then a else b	one of two values	If and Else

The order operators are worked out in

When an expression has several operators, the ones higher in this list go first. Operators on the same line go from left to right, except **, which goes right to left.

1. f(x), list[i], thing.name, thing?.name
2. **
3. - in front of a value
4. *, /, //, %
5. +, -
6. .., ..<
7. ==, !=, <, <=, >, >=, is
8. not
9. and
10. or
11. if ... then ... else

So 2 + 3 * 4 is 14, since * comes before +, and not a == b means not (a == b). and comes before or, so true or false and false is true or (false and false), which is true:

print(2 + 3 * 4)
print(true or false and false)
print(1 + 1..2 + 2)

Output

14
true
2..4

The last line is (1 + 1)..(2 + 2), because arithmetic comes before a range.

Two cases often surprise people. -2 ** 2 is -4, because ** comes before the minus sign, as it does in math; write (-2) ** 2 for 4. And 2 ** 3 ** 2 is 2 ** 9, because ** goes right to left.

When an expression mixes several levels, parentheses make it clear to the reader, even when they don’t change the answer.

What Emerald doesn’t have

If you know another language, some familiar operators are missing on purpose:

• &&, ||, and ! are spelled and, or, and not.
• ++ and -- don’t exist; write count += 1.
• %= and **= don’t exist; write x = x % y and x = x ** y.
• There is no ? :; write if c then a else b.
• in isn’t an operator; a list answers with list.contains?(item).

What you’ve learned

• Arithmetic, comparison, and logic operators, and the assignment shortcuts, are all in the tables above.
• Operators higher in the order are worked out first; parentheses override the order and make it plain.

Next, if and else: making decisions.