A silly example that lets us do several of those things with funtions:
(define(double procedure) (lambda(x) (procedure(procedure x))))
So what does this do? Well it's a function that takes a procedure of some argument x and returns another function that applies the procedure twice to x.
(
(double 1+)
3)
results in 5. (add one to three twice). It is the same as typing (1+
(1+ 3)
)
(
(double cube)
3)
results in 19683. Cube the cube of 3. It is the same as typing (cube
(cube 3)
)
where cube is defined as (define
(cube x) (* x x x)
)
These days it's not that exciting that a language supports first-class functions. C doesn't. Ruby doesn't allow nested functions but supports the other things. Fortran doesn't support anonymous functions. Java only partially supports first class functions. But Scheme's support for first class functions is probably part of why it has survived as a usable language in spite of being 43 years old. For example aisleriot, gnome's solitaire game that supports 88 varieties of solitaire, is written in Scheme and GIMP's extensions are written in Scheme. We've been looking at the basic building blocks, but there are libraries for running a web server or building gtk applications.
Mod notes:
Happy New Year![/area]
