Operators

Operators are worked out by the five commands that calculate: set, if, while, until and return. Every operator has to be a separate word, with spaces around it; see Expressions.

Arithmetic

Example	Operator	Result
%a + %b	Addition
%a - %b	Subtraction
%a * %b	Multiplication
%a / %b	Division	Whole numbers only: the remainder is dropped, 7 / 2 is 3. Dividing by 0 gives 0.
%a % %b	Remainder	What is left over after dividing: 7 % 2 is 1. By 0 it gives 0.
abs %a	Absolute value	The value without its sign: abs -5 is 5.

Arithmetic works on whole numbers. A value that is not a number (hello, N/A) counts as 0.

Comparison

Comparisons give -1 (#true) or 0 (#false).

Example	Operator	True when
%a = %b	Equal	Both are the same. When either is not a number they are compared as text, ignoring case.
%a <> %b	Not equal	They are not the same, by the same rule.
%a < %b	Less than	%a is smaller.
%a > %b	Greater than	%a is larger.
%a <= %b	Less than or equal	Also written =<.
%a >= %b	Greater than or equal	Also written =>.
%a in %b	Contained in	The text %a appears inside %b, ignoring case.
%a notin %b	Not contained in	It does not.

<, >, <= and >= are always false when either side is not a number: hello > 33 is false, and so is hello < 33. That makes a quick test for “is this a number?”:

set %cnt hello
if ! ( %cnt > 0 || %cnt < 1 )
  set %cnt 0                     ; %cnt was not a number
display ok %cnt
halt

Logical

Example	Operator	True when
%a && %b	And	Both are true.
%a || %b	Or	At least one is true.
! %a	Not	%a is false (it turns -1 into 0 and 0 into -1).

These are meant for true/false values (-1 and 0), such as the results of comparisons. On other numbers they work bit by bit (! 5 is -6), which is rarely what you want. Both sides of && and || are always worked out.

Text and lines

These are handled while the line is read, before the command runs, so they work with every command, not just the five above.

Example	Operator	What it does
%a , %b	Join	Joins the two values into one word: with %a = A and %b = B, %a , %b is AB.
%a . %b	Glue a name	Glues the word on the left to the value on the right, then reads the result as a variable. See below.
+ at the start of a line	Continue	The line continues the previous one, joined without a space.

Joining works on any word, even command names: h , a , l , t is halt.

Building variable names with .

. works from right to left: the right side is replaced by its value first, then glued to the left word, and the result is read as a variable. That builds variable names from other values, a little like arrays:

set %a 3
set %item3 sword
set %x %item . %a          ; %item . 3  ->  %item3  ->  sword
set %y %item , %a          ; "%item" has no value, so N/A , 3  ->  N/A3
display ok %x %y
halt

set %slot1 sword
set %slot2 shield
set %slot3 helmet
for %i 1 3
{
  set %name %slot . %i     ; %slot1, %slot2, %slot3
  display ok %name
}
halt

A . or , only works as a separate word. To put a full stop or a comma into text, use #DOT or glue the pieces with ,.

Order of operations

Within each pair of parentheses, starting with the innermost, operators are worked out in this order. Operators on the same row are worked out from left to right.

Order	Operators
1	! and abs, from right to left
2	* / %
3	+ -
4	= <> < > <= >= in notin
5	&&
6	||

Before any of this, while the line is read, . (right to left) and then , (left to right) have already been applied, and variables have been replaced by their values.

set %r 5 + 3 * 2               ; 5 + ( 3 * 2 ) = 11
set %r 8 - 3 - 2               ; ( 8 - 3 ) - 2 = 3
set %r ( 1 + 2 ) * 2 * 4       ; 24
set %a 1
set %b 2
if %a = 1 && %b = 2            ; ( %a = 1 ) && ( %b = 2 )
  display ok Both are true.
if ! ( %a = 1 )                ; parentheses needed: ! %a = 1 means ( ! %a ) = 1
  display ok Not shown: %a is 1.
halt

Based on the EasyUO wiki, edited for EasyUO Reforged. This text is available under the GNU Free Documentation License 1.2.