Clojure Weekly, Apr 13th, 2015
Welcome to another issue of Clojure Weekly! Here I collect a few links, normally 4/5 urls, pointing at articles, docs, screencasts, podcasts and anything else that attracts my attention in the clojure-sphere. I add a small comment so you can decide if you want to look at the whole thing or not. I also maintain a similar Haskell Weekly if you’re so inclined. That’s it, enjoy!
cloxp Here’s an interesting project. Be sure to attend the Clojure/West incoming session about it. I’ve used Squeak a few times and I’m familiar with the Smalltalk concept of a “live system”, so I was pleased to see something similar where the running code is Clojure. It gets far enough to sound interesting: code evaluation, completion, namespace browsing, LightTable-like instarepl. The idea is that between the several open scratch pads containing Clojure code you build an interacting system. It also comes with a “distraction free” format in which a white, full-screen desktop decorated with Clojure code is all you see.
Down the Clojure Rabbit Hole I attended CGrand's keynote while at FP Days 2014. I was also lucky enough to spend most of the intra-talk time talking with him about a lot of subjects and I'm still digesting that big queue of resources. The talk is dense, especially if you read "in between slides". Some non-exhaustive sample of influential concepts in functional programming: pragmatic use of parenthesis, persistent data structures as numerical systems (see Okasaki), finger trees, validators to enforce invariants, ordering considered harmful. It goes then more into HTML parsing and new ideas in that direction with Enliven. Now time to watch it, enjoy.
Clojure at a Real Estate Portal | Pithering About Nicely written. I enjoy the same positive pragmatic feeling using Clojure every day. I'm not sure if there are contexts in which this initial ease is NOT going to payoff (maybe it depends on my limited experience observing large dynamically typed codebases evolving over time). Having started some Haskell lately, I have the impression that also statically typed FP (not just OO) can suffer from the same mindset to try to figure out correct types up-front. Of course sane discipline and smart developers can overcome this or any other trouble in any language, but still, it brought back a bit of my Java years. Congrats to the team for the great delivery, another example to illustrate real-life Clojure projects aren't really hard to find anymore.
Clojure style: defn- vs. letfn - Stack Overflow This isn't just about style. Letfn allows ahead-of-definition use of functions, similar to (declare). Or as the answer points out, mutual recursion. The same wouldn't be possible with plain let of a list of functions. Then in terms of style, you'd rather use letfn when the function being defined is intended for internal use of another function only. One case is for example iterative-process recursion requiring "results" to be carried over the next computation (and when loop-recur can't be used because it's not in tail position).
razum2um/clj-debugger A basic interactive debugger. It remembers me of something similar in ruby-land called ruby-debugger. Here's a scenario: your Clojure app is having trouble you enter the REPL and redefine a couple of fns with printlns but they throw a lot of stuff at the screen that is uneasy to follow. You iterate this cycle several times tweaking the print until you can see the problem. With something like clj-debugger the process becomes interactive: you stop at the line and inspect locals, stub results and move forward.
clojure.core/test Nope, this is not clojure.test (the most basic of the Clojure test frameworks). This is even more basic and was there since Clojure 1.0. If you annotate a function with metadata that has a :test keyword, you can then invoke (test myfn) and the function at :test will be invoked. This way the testing function will be very close to the function definition (right at the top). Why this could be useful? For quick tests without the need to create a new namespace. Or maybe some creative side-effect. Along with :pre and :post this is the most basic testing facility out of the box.
shuffle Forgot to mention shuffle in the standard library. It returns a random permutation of the collection given as input. With this one Clojure is playing smart and delegating down to Java Collections.shuffle() method, which is linear time (I think what is described there is the Fisher-Yates at the end).
