It’s not idiomatic to run Clojure scripts over and over from the command line. The REPL is a better command line. Clojure being a Lisp, it’s common to fire up Clojure and leave the same instance running forever, and interact with it rather than restart it. You can change functions in the running instance one … Read more
There’s a symbol + that you can talk about by quoting it: user=> ‘+ + user=> (class ‘+) clojure.lang.Symbol user=> (resolve ‘+) #’clojure.core/+ So it resolves to #’+, which is a Var: user=> (class #’+) clojure.lang.Var The Var references the function object: user=> (deref #’+) #<core$_PLUS_ clojure.core$_PLUS_@55a7b0bf> user=> @#’+ #<core$_PLUS_ clojure.core$_PLUS_@55a7b0bf> (The @ sign is … Read more
It’s pretty well-known that general function equality is undecidable in general, so you’ll have to pick a subset of the problem that you’re interested in. You might consider some of these partial solutions: Presburger arithmetic is a decidable fragment of first-order logic + arithmetic. The universe package offers function equality tests for total functions with … Read more
This is caused by lazyness – map returns a lazy sequence which is defined inside the binding but is evaluated outside. You need to force the evaluation from inside: (binding [*out-dir* “/home/dave”] (doall (map #(str *out-dir* %) [1 2 3])))
Yes, it’s a performance optimization. I’ts not just about not calling concat – it’s about the fact that & in the argument list requires a collection to be created as well. The clojure core libraries tend to take performance seriously, under the assumption that the basic building blocks of the language will be present in … Read more
The documentation for the -> and ->> macros state that the forms after the first parameter are wrapped into lists if they are not lists already. So the question is why does this not work for #() and (fn ..) forms? The reason is that both forms are in list form at the time the … Read more
There are two good ways to do this. Which is best depends on the specific circumstance. The first is reflection: (clojure.lang.Reflector/invokeConstructor (resolve (symbol “Integer”)) (to-array [“16”])) That’s like calling (new Integer “16”) …include any other ctor arguments you need in the to-array vector. This is easy, but slower at runtime than using new with sufficient … Read more
#(println “Hello, world!”) -> no arguments #(println (str “Hello, ” % “!”)) -> 1 argument (% is a synonym for %1) #(println (str %1 “, ” %2 “!”)) -> 2 arguments and so on. Note that you do not have to use all %ns, the number of arguments expected is defined by the highest n. … Read more
subvec is probably the best way. The Clojure docs say subvec is “O(1) and very fast, as the resulting vector shares structure with the original and no trimming is done“. The alternative would be walking the vector and building a new one while skipping certain elements, which would be slower. Removing elements from the middle … Read more
An alternative to source (which should be available via clojure.repl/source when starting a REPL, as of 1.2.0. If you’re working with 1.1.0 or lower, source is in clojure.contrib.repl-utils.), for REPL use, instead of looking at functions defined in a .clj file: (defmacro defsource “Similar to clojure.core/defn, but saves the function’s definition in the var’s :source … Read more