Define a procedure that computes a square root with Newton's method:

Perform a calculation on demand and cache the result:

Definitions for unevaluated expressions can implement call-by-name semantics:

The global variable has been modified:

The right side of an immediate definition is evaluated when the definition is made:

The right side of a delayed definition is evaluated each time the definition is used:

The arguments of the left side of a definition are evaluated before the definition is made:

Definitions with the same left side overwrite earlier ones:

The pattern variable is renamed if necessary inside a nested scope:

Delayed assignment introduces a scope that is not affected by global variables:

Immediate assignment does not introduce a scope:

Use a rule to do a transformation to a particular expression:

Use a definition to do a transformation automatically for all expressions involving g:

More specific definitions are put in front of more general ones:

Definition prints definitions associated with a symbol:

Information prints various information about a symbol, including any definitions:

DownValues returns a list of rules corresponding to any downvalues defined:

Use Unset (=.) to clear definitions with a particular left-hand side:

Clear any definitions, but not attributes:

Use ClearAll to clear attributes, too:

Omitting the _ defines a transformation only for a literal value, rather than a function:

Using delayed definitions may have unexpected consequences:

The definition actually made and its behavior:

Use Evaluate to force evaluation of the right-hand side:

Or use Set to force evaluation of the right-hand side:

An iterative runaway definition:

By providing a base case, the iteration terminates:

A recursive runaway definition:

By providing a base case, the recursion terminates:

Dynamic programming for the Fibonacci sequence:

New definitions have been added during the calculation: