Answering in Clojure terms, here are some examples from Sean Devlin’s screencast: (def a-promise (promise)) (deliver a-promise :fred) (def f (future (some-sexp))) (deref f) Note that in the promise you are explicitly delivering a value that you select in a later computation (:fred in this case). The future, on the other hand, is being consumed … Read more
Literal Octals At one point I was reading in a matrix which used leading zeros to maintain proper rows and columns. Mathematically this is correct, since leading zero obviously don’t alter the underlying value. Attempts to define a var with this matrix, however, would fail mysteriously with: java.lang.NumberFormatException: Invalid number: 08 which totally baffled me. … Read more
Built-in: user> (def v [“one” “two” “three” “two”]) #’user/v user> (.indexOf v “two”) 1 user> (.indexOf v “foo”) -1 If you want a lazy seq of the indices for all matches: user> (map-indexed vector v) ([0 “one”] [1 “two”] [2 “three”] [3 “two”]) user> (filter #(= “two” (second %)) *1) ([1 “two”] [3 “two”]) user> … Read more
Let’s not forget that trusty old into lets you take anything seqable (list, vector, map, set, sorted-map) and an empty container you want filled, and puts it into it. (into [] ‘(1 2 3 4)) ==> [1 2 3 4] “have a lazy list and want a vector” (into #{} [1 2 3 4]) ==> … Read more
My personal list of reasons for preferring Clojure to other Lisps (p.s. I still think all Lisps are great!): Runs on the JVM – hence gets automatic access to the fantastic engineering in the JVM itself (advanced garbage collection algorithms, HotSpot JIT optimisation etc.) Very good Java interoperability – provides compatibility with the huge range … Read more
doall is all you need. Just because the seq has type LazySeq doesn’t mean it has pending evaluation. Lazy seqs cache their results, so all you need to do is walk the lazy seq once (as doall does) in order to force it all, and thus render it non-lazy. seq does not force the entire … Read more
You might like to read this paper by Richard Gabriel. It is a summary of the issues that the Lisp community were discussing in Lisp1 vs Lisp2. It’s a bit dense and slow moving in the first few sections, but is much easier to read by the time you get past section 5. Basically, Lisp1 … Read more
user=> (doc name) ————————- clojure.core/name ([x]) Returns the name String of a string, symbol or keyword. nil user=> (name :var_name) “var_name”
Compojure explained (to some degree) NB. I am working with Compojure 0.4.1 (here’s the 0.4.1 release commit on GitHub). Why? At the very top of compojure/core.clj, there’s this helpful summary of Compojure’s purpose: A concise syntax for generating Ring handlers. On a superficial level, that’s all there is to the “why” question. To go a … Read more
I’ve used Clojure for: Scraping web pages Shell scripts Building websites Playing around with OpenGL Writing async webservers HTML Templating Running parallel tasks (fetching multiple URLs and process in parallel) Playing around with real time audio Simulations That’s the practical / fun stuff. But Clojure has plenty of theoretical depth as well. Ideas that will … Read more