This is documentation for Mathematica 9, which was
based on an earlier version of the Wolfram Language.
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Defining Variables and Functions

The symbolic language paradigm of Mathematica takes the concept of variables and functions to a new level. In Mathematica a variable can not only stand for a value, but can also be used purely symbolically. And building on Mathematica's powerful pattern language, "functions" can be defined not just to take arguments, but to transform a pattern with any structure.

ReferenceReference

x=... set a variable

f[x_]:=... define a function that takes any single argument

Assignments »

Set (=) immediate assignment (right-hand side evaluated immediately)

SetDelayed (:=) delayed assignment (right-hand side evaluated only when used)

Unset (=.) unset a variable

Clear clear a function definition

Function Argument Patterns »

__(BlankSequence) ▪ p|p(Alternatives) ▪ p:e (Optional)

Bodies of Functions »

Module, ... scope local variables

e;e;e (CompoundExpression) execute expressions in sequence

Function Attributes »

Attributes ▪ Flat ▪ Orderless ▪ Listable ▪ HoldFirst ▪ Protected