Expressions, operators and statements

Expressions

An expression is a series of values and operators that evaluate to a new value:

3 + 5 // => 8
size("Hello") // => 5
size("Hello")*2 // => 10
(10 > 5) // => 1
(5 > 10) // => 0

When using an expression inside MEL command syntax you must surround the expression with parentheses, and not use unquoted strings:

string $object = "cake";
setAttr $object.tx 2; // Wrong
setAttr ($object + .tx) 2; // Wrong
setAttr ($object + ".tx") 2; // Right

Maya also uses the word expression to refer specifically to bits of code you can attach to an attribute to drive animation.

• Animation expressions
• Creating animation expressions

Operators

A binary operator requires two operands, one before the operator and one after the operator:

operand1 operator operand2

For example:

3 + 4
$x = 5
$bool1 or $bool2

A unary operator requires a single operand, either before or after the operator:

operator operand

or

operand operator

For example:

$x++ // Increments the value of $x by one.

In addition, MEL has one ternary (three operand) operator:

condition ? exp1 : exp2

Statements

A statement is a structure of keywords and expressions that control the flow of the program:

if (condition)
	exp1
else
	exp2
while (condition)
	exp1