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Mathematica > Core Language > Rules & Patterns > Rules > RuleDelayed (:>, ⧴) >

BUILT-IN MATHEMATICA SYMBOL

RuleDelayed

represents a rule that transforms lhs to rhs, evaluating rhs only after the rule is used.

holds its right-hand side unevaluated:

The right-hand side is evaluated separately each time it is used:

holds its right-hand side unevaluated:

Out[1]=

The right-hand side is evaluated separately each time it is used:

Out[2]=

Increment

each time

is replaced:

Evaluate the StepMonitor expression separately each time it is to be used:

Generate a diagonal matrix with random elements:

evaluates when it is first entered;

when it is used:

Module and With do not affect local variables of RuleDelayed:

Module effectively uses a renamed instance of

By evaluating the arguments to RuleDelayed, local scoping is avoided: