5 ms·

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.

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#%_sec_1.1.7 http://mitpress.mit.edu/sicp/full-text/book/book-Z-H-10.html...

lisper 13y ago
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.
- obblekk 13y ago
  scheme lists aren't lazily generated?
  - davexunit 13y ago
    You use streams a la SRFI-41 for this.
    - brudgers 13y ago
      Or Lazy Racket [in so far as Racket is a Scheme]. http://docs.racket-lang.org/lazy/ http://docs.racket-lang.org/lazy/
- dmunoz 13y ago
  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.html#%_sec_3.5 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.html#%_sec_4.2 https://mitpress.mit.edu/sicp/full-text/book/book-Z-H-27.htm...
crntaylor 13y ago
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.pdf http://www.cs.kent.ac.uk/people/staff/dat/miranda/whyfp90.pd...

lisper 13y ago

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.

obblekk 13y ago
scheme lists aren't lazily generated?
- davexunit 13y ago
  You use streams a la SRFI-41 for this.
  - brudgers 13y ago
    Or Lazy Racket [in so far as Racket is a Scheme]. http://docs.racket-lang.org/lazy/ http://docs.racket-lang.org/lazy/
dmunoz 13y ago
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.html#%_sec_3.5 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.html#%_sec_4.2 https://mitpress.mit.edu/sicp/full-text/book/book-Z-H-27.htm...

crntaylor 13y ago

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