Clojure/West 2013 in 30 mins

Leonardo Borges@leonardo_borgeshttp://www.leonardoborges.comhttp://www.thoughtworks.com

Clojure/West 2013 in 10-ish mins

Saturday, 30 March 13

http://www.leonardoborges.com


http://www.thoughtworks.com


Day 1


DDD in Clojure - Amit Rathore @amitrathore



OO can still teach us a thing or two



In OO:- nouns- processes owned by nouns- nouns are classes- processes are methods



In OO:- nouns- processes owned by nouns- nouns are classes- processes are methods

In Clojure:- verbs- domain model: functions that transform data



A few general guidelines for your domain:- no side-effects- no dependencies on external services- validate outside the model boundary (validateur, bouncer, clj-scheme)- no illegal state in domain functions (slingshot)



Namespace organisation at Zolo:

- main namespace called core (most projects do this)- zolo.models.(user | contacts | …)- zolo.gateway.(facebook | linkedin | twitter | …)- zolo.utils.(calendar | strings | maps | …)- zolo.api.*- zolo.services.(user-service | …)



When you have no idea:

- zolo.homeless.*



Still relevant:

- SOLID principles- Few public fns (lots of private, helper fns)- small fns (3-4 lines)- optimize for readability


RESTful Clojure - Siva Jagadeesan



Richardson Maturity Model



Richardson Maturity Model

?Saturday, 30 March 13


Richardson Maturity Model:- Level 0- Level 1: Resources- Level 2: HTTP Verbs- Level 3: Hypermedia



Level 0- GET /api?action=create_order&param1=val1- GET /create_order?param1=val1



Level 1 - Resources- GET /orders?action=create&param1=val1



Level 2 - HTTP Verbs- GET /orders- POST /orders ( includes body payload)



Level 3 - Hypermedia- GET /orders- POST /orders ( includes body payload)



Level 3 - Hypermedia- GET /orders- POST /orders ( includes body payload)

{ "id": 1, "items": [ { "id": 2 } ], "link": { "rel": "delete", "href": "/orders/1" }}


Engines of Abstraction - Jim Duey


Engines of Abstraction - Jim DueyAh, one more monads talk!

- Monoids in clojure - list, concat, set, union, hash-map...

- Functors - a context datatype and a fn (fmap) to apply a function to each value inside that context

- Applicative Functors - a context datatype and two functions: one that wraps a value in the context type 'amap' applies fns wrapped in the context to parameters wrapped in the context

- Monads - context data type, fn that wraps values, fn (bind) to apply a fn to wrapped values. The applied fn takes a value and returns a wrapped value.


Engines of Abstraction - Jim Duey

Who wants a monads talk at #cljsyd? :)


Clojure in the Large - Stuart sierra



Lisp is a ball of mud- not a lot of structure: namespaces and vars. That’s it.- namespaces: not first-class modules- def and defn are global by default

Also talked about encapsulation and global state



Encapsulation anti-pattern:

;; Tempation to share it promiscuously!(def state-a (ref {}))

;; Hidden dependencies(defn op1 [] (dosync (alter state-a ...)))



Encapsulation: use local-state instead

;; Well-defined initial state. 'Go together' semantics(defn constructor [] {:a (ref {}) :b (atom 0)})

;; Makes function dependencies clear(defn op1 [state] (dosync (alter (:a state) ...)))



with-* macros:- assumes body starts and ends in a single thread- assumes doesn’t return lazy seqs- limits caller to one resource at a time



Anti-pattern - thread-bound state:

(def ^:dynamic *resource*)

(defn- internal-op1 [] ... *resource* ...)

;;another hidden dependency(defn op1 [arg] (internal-op1 ...))



Local state with dynamic extent: nested with-resources;; Pass around "context" argument(defn op1 [context] ;; not confined to a single thread ;; acquire resources (let [resource (::resource context)] ;; use namespace qualified keys (assoc context ::result1 ...)))

;; still need to manage resource lifecycle(defn finish [context] (update-in context [::resource] dispose))



When is it safe to use global Vars?- True constants: (def ^:const gravity 6....)- True singletons: (def runtime (Runtime/getRuntime))- For REPL dev- Private dynamic vars are OK: (def ^:private ^:dynamic *state*)

(binding [*state* ....] ...)


Pedestal

No point in showing it here. Go to http://pedestal.io/


http://pedestal.io

http://pedestal.io

Beyond contracts - Paul deGrandis


Beyond contracts - Paul deGrandis

core.specs: automatically generate tests and documentation and contracts from REPL explorations:

https://github.com/ohpauleez/sterling




Day 2


PuppetDB - centralised DB for Puppet developed in Clojure


PuppetDB - centralised DB for Puppet developed in Clojure

Why Clojure?- Issues with Ruby: slow, GIL, garbage collection

Puppet DB is a layer on top of PostgreSQL

Write pipeline:- async, parallel, MQ-based, automatic retry

Read pipeline:- DLS, AST-based, transferred over the wire using JSON- you can write your own


Securing Clojure Web Apps/Services with Friend - Chas Emerick



- Authentication and Authorization library for Clojure- Ring middleware



Batteries included: - Authentication workflows - form-based "interactive" login - HTTP basic (Digest, soon) - OpenId (Google, Yahoo, Wordpress etc...) - "Channel enforcement" (e.g. require HTTPS)

- Authorization Options - Roles based on Clojure's ad-hoc hierarchies - functions, macros, and ring middleware for enforcinf role-based auth policy - Arbitrary imperative control



https://github.com/cemerick/friend




pallet.clj - Infrastructure project file


pallet.clj - Infrastructure project file

pallet-lein plugin: https://github.com/pallet/pallet-lein

create pallet.clj file

> lein pallet up <-- local

or on EC2...


https://github.com/pallet/pallet-lein

https://github.com/pallet/pallet-lein

clj-v8 and the dieter asset pipeline


clj-v8 and the dieter asset pipeline

JS/CSS minification, concatenation and cache busting: https://github.com/edgecase/dieter


https://github.com/edgecase/dieter

https://github.com/edgecase/dieter

Day 3


Ritz - The missing Clojure tooling: https://github.com/pallet/ritz


https://github.com/pallet/ritz

https://github.com/pallet/ritz

Macros vs. Monads


Macros vs. Monads

Synthread: https://github.com/LonoCloud/synthread- Presented as an alternative do the state monad:

(require '[synthread :as ->])

(-> {} f1 f2 f3)


https://github.com/LonoCloud/synthread

https://github.com/LonoCloud/synthread

Macros vs. Monads

And it’s got lots of other useful macros: ->/do ->/if ->/when ->/for ->/assoc ->/update-in


The EndQuestions?

Leonardo Borges@leonardo_borges

http://www.leonardoborges.comhttp://www.thoughtworks.com






Clojure/West 2013 in 30 mins

Documents

clojure amit rathore

clojure list

resource context

context monads

context datatype

nouns nouns

orders post orders

large stuart sierralisp