[AlexanderDhoore]

Am I dreaming, or is this an example straight from SICP? (I remember something like this...)

EDIT: Ok, so obviously not "straight" from SICP. But pretty close.

Chapter 1: "Example: Square Roots by Newton's Method" http://mitpress.mit.edu/sicp/full-text/book/book-Z-H-10.html...

[crntaylor]

SICP has something to do with square roots in the first chapter, although I don't think they do this particular refactoring. I first saw it (or something like it) in John Hughes' Why Functional Programming Matters.

Which, by the way, is an excellent paper and totally worth reading.

http://www.cs.kent.ac.uk/people/staff/dat/miranda/whyfp90.pd...

[lisper]

Well, it can't be straight out of SICP because SICP uses Scheme and this code is in Haskell. And, in fact, if you did a straightforward translation of the Haskell code back into Scheme it wouldn't work. Figuring out why it doesn't work in Scheme but it does in Haskell is left as an exercise.

[dmunoz]

Of course, in later chapters SICP covers both streams [0] and lazy evaluation in the interpreter [1]. It's a really great book! I'm completely jealous of anyone who was introduced to CS via a serious studying of SICP.

[0] https://mitpress.mit.edu/sicp/full-text/book/book-Z-H-24.htm...

[1] https://mitpress.mit.edu/sicp/full-text/book/book-Z-H-27.htm...

[obblekk]

scheme lists aren't lazily generated?

[davexunit]

You use streams a la SRFI-41 for this.

[brudgers]

Or Lazy Racket [in so far as Racket is a Scheme].

http://docs.racket-lang.org/lazy/