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
Here’s my take on it. I made a point of only using Clojure data structures to see how that would work out. Note that it would have been perfectly usual and idiomatic to take a blocking queue from the Java toolbox and use it here; the code would be easy to adapt, I think. Update: … Read more
I normally call (keys (ns-publics ‘foo)) to list Vars exported by the namespace foo; e.g. for clojure.contrib.monads this returns (defmonad censor m-when-not m+write+m maybe-m maybe-t …) (the … stands for quite a lot more). More generally, there’s a bunch of functions whose names start in ns- which list Vars by namespace, with certain additional criteria … 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
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
CORRECTED TWICE: A simpler way to un-chunk a lazy sequence: (defn unchunk [s] (when (seq s) (lazy-seq (cons (first s) (unchunk (next s)))))) First version omitted (when … so it returned an infinite seq of nil’s after the input sequence ended. Second version used first instead of seq so it stopped on nil. RE: your … Read more
require loads libs (that aren’t already loaded), use does the same plus it refers to their namespaces with clojure.core/refer (so you also get the possibility of using :exclude etc like with clojure.core/refer). Both are recommended for use in ns rather than directly.
The usual solution is (defn transpose [m] (apply mapv vector m))
(:color my-car) is fairly standard. There are a few reasons for this, and I won’t go into all of them. But here’s an example. Because :color is a constant, and my-car is not, hotspot can completely inline the dynamic dispatch of color.invoke(m), which it can’t do with m.invoke(color) (in some java pseudo-code). That gets even … Read more
Zip is when you take two input sequences, and produce an output sequence in which every two elements from input sequences at the same position are combined using some function. An example in Haskell: Input: zipWith (+) [1, 2, 3] [4, 5, 6] Output: [5, 7, 9] The above is a more generic definition; sometimes, … Read more