reduce and apply are of course only equivalent (in terms of the ultimate result returned) for associative functions which need to see all their arguments in the variable-arity case. When they are result-wise equivalent, I’d say that apply is always perfectly idiomatic, while reduce is equivalent — and might shave off a fraction of a … Read more
In Prolog’s terms, condA is “soft cut” a.k.a. *->, where A *-> B ; C is like (A, B ; not(A), C), only better ; whereas condU is “committed choice”, a combination of once and a soft cut so that (once(A) *-> B ; false) expresses (A, !, B) (with the cut inside): condA: A *-> … Read more
The difference is that for builds a lazy sequence and returns it while doseq is for executing side-effects and returns nil. user=> (for [x [1 2 3]] (+ x 5)) (6 7 8) user=> (doseq [x [1 2 3]] (+ x 5)) nil user=> (doseq [x [1 2 3]] (println x)) 1 2 3 nil … Read more
Yes, there is a “next permutation” algorithm, and it’s quite simple too. The C++ standard template library (STL) even has a function called next_permutation. The algorithm actually finds the next permutation — the lexicographically next one. The idea is this: suppose you are given a sequence, say “32541”. What is the next permutation? If you … Read more
Since Java varargs are actually arrays, you can call vararg functions in Clojure by passing an array. You could convert a Clojure seq (maybe by using Clojure’s variety of variable argument functions) into an array: (TestClass/aStaticFunction (into-array Integer [(int 1),(int 2)])) or (defn a-static-function-wrapper [& args] (TestClass/aStaticFunction (into-array Integer args)) Or make an array and … Read more
Record update syntax comes standard with the compiler: addManStk team = team { manager = (manager team) { diet = (diet (manager team)) { steaks = steaks (diet (manager team)) + 1 } } } Terrible! But there’s a better way. There are several packages on Hackage that implement functional references and lenses, which is … Read more
Try: /(?!.*bar)(?=.*foo)^(\w+)$/ Tests: blahfooblah # pass blahfooblahbarfail # fail somethingfoo # pass shouldbarfooshouldfail # fail barfoofail # fail Regular expression explanation NODE EXPLANATION ——————————————————————————– (?! look ahead to see if there is not: ——————————————————————————– .* any character except \n (0 or more times (matching the most amount possible)) ——————————————————————————– bar ‘bar’ ——————————————————————————– ) end of … Read more
Just use :resource-paths in your project.clj file. I use it, e.g. to connect to Siebel servers. Just created a resources directory in my project directory and copied the jar files in there. But of course you could use a more generic directory: (defproject test-project “0.1.0-SNAPSHOT” :description “Blah blah blah” … :resource-paths [“resources/Siebel.jar” “resources/SiebelJI_enu.jar”]) Then from … Read more
Yes, a Var in Clojure is similar to a C pointer. This is poorly documented. Suppose you create a function fred as follows: (defn fred [x] (+ x 1)) There are actually 3 things here. Firstly, fred is a symbol. There is a difference between a symbol fred (no quotes) and the keyword :fred (marked … Read more
You’re being hit by filter‘s laziness. Change (filter …) to (doall (filter …)) in your recur form and the problem should go away. A more in-depth explanation: The call to filter returns a lazy seq, which materialises actual elements of the filtered seq as required. As written, your code stacks filter upon filter upon filter…, … Read more