1 Expressions

Expressions are used in:

• the right side of an assignment instruction,
• in the conditions of IF, DO, and WHEN clauses,
• in the initial values of iterative DO control values (TO, BY, FOR),
• as the repetitor clause of a simple iterative DO,
• as the settings for NUMERIC processing option values,
• the arguments of function calls, and CALL instructions,
• in the VALUE ... WITH clause of a PARSE, ARG, or PULL instruction,
• in the VALUE clause of the TRACE instruction,
• as well as SAY, ADDRESS, OPTIONS, PUSH, QUEUE, RETURN, EXIT, and INTERPRET instructions.

The general form of an expression is one of the following:

Form:	Examples:
term	42 'red' isPrime.x.y
prefixOperator term	- 42 \ isPrime
term operator term	6 * 7 'your name is' first_name last_name This expression uses space concatenation operators. 7 < random( 1, 10 )

1.1 Terms

Expression terms can be one of the following:

string	'open sesame' "This isn't a numeric value"
hexadecimal string	'2 2bad'x
binary string	'1 01'b
symbol	42 1.23e+42 '   +  7.9E42  ' first_name isPrime.x.y isPrime.
function result	left( 'abracadabra', 4 )
parenthesized expression	(2 + 2) (2 + (6 * 3)) ('your name is' name)

Furthermore, wherever a term can appear an expression can appear!

Here is an assignment instruction with an intricate expression:

vector = left( ' ', 8 * day1no ) || , overlay( ' > 'right( dayofmon, 2 )' < ' , , left( ' 1 2 3 4 5 ' || , ' 6 7 8 9 10 ' || , ' 11 12 13 14 15 ' || , ' 16 17 18 19 20 ' || , ' 21 22 23 24 25 ' || , ' 26 27 28 29 30 ' || , ' 31 ', (daysinmo * 8) ), , 1 + ((dayofmon-1) * 8) )

1.2 Operators

1.2.1 Concatenation operators

(space)	date() time()	the space between the functions is an operator
(abuttal)	date() || time()	the '||' operator is an explicit abuttal operator
(abuttal)	date()' at 'time()	the quoted string is implicitly concatenated to the adjacent terms

Rexx has two fundamental string concatenation operators.

1. concatenation with an intervening space -- space concatenation

2. concatenation WITHOUT an intervening space -- abuttal concatenation

Click here for a detailed description of string concatenation operators.

1.2.2 Arithmetic operators

Numeric terms can be processed with the following operators:

+	Add	21 + 21
-	Subtract	44 - 2
*	Multiply	6 * 7
/	Divide	84 / 2
%	Integer divide	85 % 2
//	Remainder	42 // 50	similar to modulo but the result can be negative
**	Power (exponent)	2 ** 4
Prefix +	(0 + number)	+ 42
Prefix -	(0 - number)	- 42

1.2.3 Comparison operators

Comparison operators compare two terms. The result of the comparison is '1' when the terms are equal, and '0' otherwise. There are two types of comparison operators -- strict and normal.

In normal comparisons, strings are compared for the length of the shorter term, and trailing spaces are ignored. The collating order of characters is implementation-dependent. There are significant differences between the ordering of characters in Ascii environments, versus EBCDIC.

When both terms in a normal comparison are numeric, then a numeric comparison is performed. '7' is less than '11' in a normal comparison.

In strict comparisons, trailing spaces are significant. Strict comparisons always compare string values, even though both terms are numeric. '7' is greater than '11' in a strict comparison!

1.2.3.1 Normal comparisons

=	equal
¬=, \=, ><, <>	not equal
>	greater than
<	less than
>=, ¬<, \<	greater than or equal; not less than
<=, ¬>, \>	less than or equal; not greater than

Note: The ¬ operator character may be absent in Ascii implementations. The backslash character (\) is now preferred.

1.2.3.2 Strict comparisons

Strict comparison operators are similar to normal comparison operators, but has doubled operators.

==	strictly equal
¬==, \==	strictly not equal
>>	strictly greater than
<<	strictly less than
>>=, ¬<<, \<<	strictly greater than or equal; strictly not less than
<<=, ¬>>, \>>	strictly less than or equal; strictly not greater than

1.2.4 Logical (boolean) operators

Logical operators transform the boolean sense of one or two terms. A term is considered to be false if it is strictly equal to '0'. A term is considered to be true if it is strictly equal to '1'. Any values other than '0' or '1' are invalid, and cause error #34 (logical value not 0 or 1) to be raised.

&	And	returns '1' when both terms are true, and '0' otherwise
|	Or	returns '1' when either term is true, and '0' otherwise
&&	Exclusive or	returns '1' when one of the terms is true (but not both), and '0' otherwise
Prefix ¬, Prefix \	Logical not	returns '1' when the term is '0', and '0' when the term is '1'.

1.2.5 Boolean expressions

Boolean expressions are used in the condition clauses of IF, DO, and WHEN instructions,

As mentioned above, the result of a boolean expression is considered to be false if it is strictly equal to '0'. A term is considered to be true if it is strictly equal to '1'. Any values other than '0' or '1' are invalid, and cause error #34 (logical value not 0 or 1) to be raised.

Some examples are helpful.

if number < limit then ...	ok, hopefully both variables have numeric values
when result then ...	oops, what if result is not exactly '0' or '1'
do while lines( )	oops, you probably want to do: lines( ) > 0 instead