Clojure Weekly, Jul 15th, 2014
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. That’s it, enjoy!
Functional Geekery Episode 12 – Adi BolboacaFunctional Geekery | Functional Geekery Controversial (in a good sense) Functional Geekery episode. When speaking about style and idiomatic Clojure, I tend to be inspired by one of the most popular source of Clojure wisdom: clojure/core.clj. The style there leans toward essentiality, where variable names are just a few letters and they tend to follow an implicit convention (f, g are function names, xs is a collection of x and so on). But uncle Bob clean-code style is much more verbose in that respect, suggesting more speaking names. I agree with all the rest of the discussion, in term of SOLID principles applied to FP and the overall idea to dedicate a code-retreat format to FP style programming. But I'm not sure about naming. What determines understandability in a language is also the culture and conventions that are stratified into it. Clojure is inspired by CL in many ways, including naming and it looks unproductive to me to try to change 50+ years of conventional wisdom to another convention.
rseq · clojure.core For the "standard library in small pills" series, here's the mostly unknown rseq. It works like seq, transforming something sortable into a sequence but at the same time it is reversing its order. Use cases? None at hand, but consider that it is doing it O(1). How can it be? Little trickeries: the PersistentVector underneath is unchanged, but is wrapped in an RSeq object that is counting backward when next() is required, starting from the end! Good luck garbage collector when I unroll 1M of these :)
protocols - How does clojure's defrecord method name resolution work? - Stack Overflow Enlightening quick SO answer from Christophe Grand about potential name clashing in protocol definitions. defprotocol and defrecord are a powerful tool provided by Clojure to replicate some object oriented runtime polymorphism. They've got rough edges as soon as you start pushing too far with them, something you can experience if you try to port a complex object model from Java "literally". defprotocol for instance, creates the function definitions inside the namespace they are declared in, with the consequence that there shouldn't be other "normal" functions with the same name and no other protocols definitions with the same name, let alone using function names from clojure.core. At the same time if you define protocols in different namespaces you can incur in weird require+import constrains to use them in other places. Add the fact that other than the basic examples, there is no throughout guide to "build yourself a CLOS in Clojure". We can certainly discuss if this is needed at all...
lein test-refresh If only I knew about this a couple months ago... I wouldn't have ported the test suite to Midje with autotest, my favourite unit test framework. Or maybe not, because I'm quite fluent with the Midje API and got used to the expressiveness it can provide. Anyway, if you are on clojure.test, this lein plugin is an automatic runner that runs in the background and send you notifications about the status of the tests while you are typing in the editor. It is my favourite workflow at the moment, which includes the REPL running for experimentation and solutions while the overall functional interface is driven by tests. I don't use the same for legacy code, where somebody else wrote it, although I tend to cover "after" with test the part I don't understand.
L(λ)THW Learn Lisp The Hard Way Interesting initiative that could be ported to Clojure and has already been ported many times to many languages. Zed Shaw started it all (I think it was Learn C The Hard Way) and then produced another bunch of them. The template to write books using the same style is publicly available and Zed Shaw is encouraging others to write their own. This is the "brave" Lisp attempt, considering the amount of top quality books around about programming in Lisp. The author explained the effort behind this achievement on HackerNews. This is not a couple of days project and it is coming out nicely. Remember the following rule of thumb: learning Lisp is providing you the all principle (and often nomenclature and conventions) behind Clojure.
clojure.core/cycle Cycle is similar to clojure.core/repeat, but it operates on a sequence by recursively merging it to a copy of itself, ad infinitum. Cycle is your friend on things that needs to be provided in a round-robin fashion, including assignment of a finite set of identifiers or simply creating a css zebra list of some sort. Repeat is less useful here since it will repeat a single item instead. Always use with clojure.core/take on front!
