15. Lazy evaluation

Question 1

What is a reducible expression (redex)

Answer 1

An expression that has the form of a function applied to one ore more arguments that can be reduced.

Question 2

Describe innermost evaluation

Answer 2

Always choose a redex that is innermost before it is passed into a function.

Question 3

Describe ‘passed by value’

Answer 3

The arguments are fully evaluated before being passed into a function.

Question 4

Describe outermost evaluation

Answer 4

Always evaluate an expression before evaluating it’s arguments.

Question 5

Describe ‘passed by name’

Answer 5

The function is applied before the arguments have been evaluated

Question 6

which one is prefered: call-by-value or call-by-name and why?

Answer 6

Call-by-name is preferable, it ensures that evaluation terminates as often as possible. Allows us to work with infinite structures.

Question 7

How do you use strict applications? Give an example

Answer 7

Using $!, forces an evaluation.
example: f $! x this forces x to be evaluated before being parsed into f.