SetDelayed

SetDelayed(expr, value)

expr := value

assigns value to expr, without evaluating value.

Examples

SetDelayed is like Set, except it has attribute HoldAll, thus it does not evaluate the right-hand side immediately, but evaluates it when needed.

>> Attributes(SetDelayed)
{HoldAll}

>> a = 1
1

>> x := a
>> x
1

Changing the value of a affects x:

>> a = 2
2

>> x
2

Condition (/;) can be used with SetDelayed to make an assignment that only holds if a condition is satisfied:

>> f(x_) := p(x) /; x>0
>> f(3)
p(3)

>> f(-3)
f(-3)

Related terms

Set, TagSet, TagSetDelayed

Implementation status

• ✅ - full supported

Github

• Implementation of SetDelayed