If there is one book that made me think differently about programming its this one.
Oh I did know common lisp, and other languages like C/C++, Python etc. But till then it was all about language features being built in for me. Which is all good and useful.
Only problem is that I didn't realize that all this can be built upon some very simple fundamental concepts. So when this book started with _only_ car, cdr and lambda and built all sorts of higher level things out of it, it was a real eye opener and I actually came to appreciate the value of a small simple core in a language.
I saw the videos before I read the book. That was helpful.
even cons, car and cdr can be done with lambda, which adds to the mind bending.
> (define (cons a b) (lambda (f) (f a b)))
> (define (car c) (c (lambda (a b) a)))
> (define (cdr c) (c (lambda (a b) b)))
> (car (cdr (cons 1 (cons 2 (cons 3 '())))))
2
Comments
If there is one book that made me think differently about programming its this one.
Oh I did know common lisp, and other languages like C/C++, Python etc. But till then it was all about language features being built in for me. Which is all good and useful.
Only problem is that I didn't realize that all this can be built upon some very simple fundamental concepts. So when this book started with _only_ car, cdr and lambda and built all sorts of higher level things out of it, it was a real eye opener and I actually came to appreciate the value of a small simple core in a language.
I saw the videos before I read the book. That was helpful.
even cons, car and cdr can be done with lambda, which adds to the mind bending.
And of course, even lambda is unnecessary. Using two combinators, customarily called s and k suffices:
This system is called the SKI-calculus (http://en.wikipedia.org/wiki/SKI_combinator_calculus). The I in SKI stands for the identity, and can be expressed in terms of s and k.As an example, here is the y-combinator: