laziness in functional programming

[John Baez <john.c.baez@gmail.com>]

Bill Lawvere wrote:


I don't know the technical meaning of "lazy"; was it an attempt to avoid the
> processing speed and ram needed to take account of the composition with
> inclusion maps, etcetera?
>

No, "lazy evaluation" is a strategy of putting off computations until their
results are known to be necessary.  The opposite is called "eager
evaluation".  Laziness is often wiser.

For example, a programming statement

x:=y

calls for the value of x to be set equal to y.  A strategy of eager
evaluation will do this right away, while lazy evaluation will put off doing
it until the variable x is used in some other task.  If x is never used,
this saves work.

I think most functional programming languages either delay evaluation in
this way, or give the user the option to do this.

Best,
jb