Lazy Evaluation - Efficiency?

Q. Does lazy evaluation always lead to more efficient computation?

A. No. Consider the Miranda code

double x = x + x

double 11*13

This evaluates as

11*13 + 11*13 = 143 + 143 = 186

But with applicative order evaluation we would have

double 11*13 = double 143 = 143 + 143 = 186

which performs less arithmetic.

Also, lazy evaluation usually incurs extra overhead.

Previous slide

Next slide

Back to first slide

View graphic version