grylix

grylix

Programming Clojure, Fourth Edition: lazy streams (p. 104)

On Page 104 you describe several ways to define lazy streams in general or the stream of the fibonacci numbers in general.

I propose to demonstrate the definition of streams as the fixed point of a given function which maps a stream to another stream. The given function must be a productive function, i.e. a function,
that can generate at least the beginning of a sequence.

(defn fixedpoint [f]
(letfn
[(stream [ ] (lazy-seq (f (stream))))]
(stream))
)

Let’s define some examples, e.g. the stream of zeros, ones, or the stream of alternating zero and ones:

(set! *print-length* 20)
(def zeros (fixedpoint (fn [s] (cons 0 s))))
(def ones (fixedpoint (fn [s] (cons 1 s))))
(def zeroone (fixedpoint (fn [s] (cons 0 (cons 1 s)))))

but more interesting is the definition of the stream of integers

(def ints (fixedpoint (fn [s] (cons 0 (map inc s)))))

and the stream of fibonacci numbers

(def fibs (fixedpoint (fn [s] (cons 0 (map + s (cons 1 s))))))

For me, this definition is very simple and clear.

Best wishes
Dominik

Where Next?

Popular Pragmatic Bookshelf topics Top

iPaul
page 37 ANTLRInputStream input = new ANTLRInputStream(is); as of ANTLR 4 .8 should be: CharStream stream = CharStreams.fromStream(i...
New
jdufour
Hello! On page xix of the preface, it says there is a community forum "… for help if your’re stuck on one of the exercises in this book… ...
New
JohnS
I can’t setup the Rails source code. This happens in a working directory containing multiple (postgres) Rails apps. With: ruby-3.0.0 s...
New
gilesdotcodes
In case this helps anyone, I’ve had issues setting up the rails source code. Here were the solutions: In Gemfile, change gem 'rails' t...
New
swlaschin
The book has the same “Problem space/Solution space” diagram on page 18 as is on page 17. The correct Problem/Solution space diagrams ar...
New
brunogirin
When installing Cards as an editable package, I get the following error: ERROR: File “setup.py” not found. Directory cannot be installe...
New
New
a.zampa
@mfazio23 I’m following the indications of the book and arriver ad chapter 10, but the app cannot be compiled due to an error in the Bas...
New
New
davetron5000
Hello faithful readers! If you have tried to follow along in the book, you are asked to start up the dev environment via dx/build and ar...
New

Other popular topics Top

AstonJ
poll poll Be sure to check out @Dusty’s article posted here: An Introduction to Alternative Keyboard Layouts It’s one of the best write-...
New
New
Exadra37
I am asking for any distro that only has the bare-bones to be able to get a shell in the server and then just install the packages as we ...
New
PragmaticBookshelf
Learn different ways of writing concurrent code in Elixir and increase your application's performance, without sacrificing scalability or...
New
PragmaticBookshelf
Build highly interactive applications without ever leaving Elixir, the way the experts do. Let LiveView take care of performance, scalabi...
New
AstonJ
Continuing the discussion from Thinking about learning Crystal, let’s discuss - I was wondering which languages don’t GC - maybe we can c...
New
Maartz
Hi folks, I don’t know if I saw this here but, here’s a new programming language, called Roc Reminds me a bit of Elm and thus Haskell. ...
New
DevotionGeo
I have always used antique keyboards like Cherry MX 1800 or Cherry MX 8100 and almost always have modified the switches in some way, like...
New
PragmaticBookshelf
Leverage Elixir and the Nx ecosystem to build intelligent applications that solve real-world problems in computer vision, natural languag...
New
PragmaticBookshelf
Develop, deploy, and debug BEAM applications using BEAMOps: a new paradigm that focuses on scalability, fault tolerance, and owning each ...
New

Sub Categories: