The ordering of reductions

2 minutes, 8 seconds

The Order of Evaluation - slide 14 : 26

Given a complex expression, there are many different orderings of the applicable reductions

Using normal-order reduction, the first reduction to perform is the one at the outer level of the expression

Using applicative-order reduction, the first reduction to perform is the inner leftmost reduction

Normal-order reduction represents evaluation by need
Applicative-order reduction evaluates all constituent expressions, some of which are unnecessary or perhaps even harmful. As such, there is often a need to control the evaluation process withspecial formsthat use a non-standard evaluation strategy