ClojureWest 2013: Day Two Notes

Winning the War on Javascript: Bodil Stokke

• catnip: beginners clojure editor in browser
• originally used coffeescript because cljs was immature and hard to work with js objects
• currently working on converting catnip to cljs
• error: another clojurescript testing framework, built around asynchronous testing

PuppetDB: Sneaking Clojure into SysAdmins’ Toolkits: Deepak Giridharaghopal

• ops has a lot of entropy: spooky action at  distance: devs or admins logging in to one of many servers and mucking around without telling you
• lack of predictability ruins automation and abstraction
• problems with previous software in Ruby: not fast, only one core, mutable state everywhere, runtime compatibility a problem
• solution: puppetdb in clojure for storing and querying data about systems
• used CQRS: command query responsibility separation -> use different model to update then to read info
• send commands to a /command endpoint, which queues the command for parsing and processing
• build command processing functions as multi-methods switching off of the command and version sent
• can also turn on live repl, to connect to running code and hack
• queries have their own AST-based syntax; sent as json, built as vector tree
• can ship the whole thing as a single uberjar, with built-in db, etc

Securing Clojure Web Services & Apps with Friend: Chas Emerick

• authentication & authorization (who are you? what are you allowed to do?)
• options: spring-security (java, not recommended), sandbar, ring-basic-authentication, clj-oauth2
• most common: roll your own
• wrote friend to have a common auth framework
• uses ad-hoc hierarchies for roles
• add workflows to specify how to authenticate a request that doesn’t have authentication yet
• friend-demo.herokuapp.com for multiple demos with source code
• recommend using b-crypt over sha

FRP in ClojureScript with Javelin: Alan Dipert

• event stream: sequence of values over time
• behavior: function that updates according to changing values from event stream
• reactive evaluation: holds off on evaluating until all values are available
• similar to spreadsheet formula evaluation (!)
• FRP maintains evaluation order despite lack of all values at once
• current FRP in clojurescript: FlapJax
• javelin: abstract spreadsheet library for reactive programming with values
• everything contained in the “cell” macro
• web app has single state at any point in time, contained in the “stem cell”
• everything in app either in stem cell or derived from it

SQL and core.logic Killed my ORM: Craig Brozefsky

• uses clojure for analysis engine looking for possible malware actions
• core.logic engine takes observations and creates IOCs (indications of compromise) + html
• observations: wrapper around core.logic’s defrel
• IOCs: severity + confidence, explanation, suggested remediation
• the reasoned schemer: handed out to all their analysts to explain logic programming to them so they can use the system

Macros: Why, When and How: Gary Fredericks

• macro: special function that takes form as argument and returns a form
• run at compile time
• can always be replaced by its expansion
• when writing macros, helps to know what you want it to expand to
• use macroexpand-1 to find out when it’s going to return
• cannot pass macro to higher-order function (not composable at runtime)
• macros can make code harder to read; person reading code has to be familiar with macro expansion to really know what your code is doing
• tolerated usage: defining things, wrapping code execution, delaying execution, capturing code, DSLs, compile-time optimizations (hiccup produces as much html as possible at compile time)
• avoiding macros: get more familiar with higher-order function usage and paradigms
• writing tolerable macros: use helper functions, naming conventions, no side effects
• syntax-quote (backtick): like quote on steroids, gives you multiple benefits when used in a macro