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Mathematica > Core Language > Rules & Patterns > Rules >

Built-in Mathematica Symbol

RuleDelayed

lhs:>rhs or lhs

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

The assignment lhs:=rhs specifies that the rule lhs:>rhs should be used whenever it applies.

:> holds its right-hand side unevaluated:

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

:> holds its right-hand side unevaluated:

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

Increment n each time x 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 y:

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