ClojureWest 2013: Day One Notes

Domain Driven Design in Clojure: Amit Rathore

read the book from eric evans
Lot of oop design principles carry over
shoot for 3-4 lines of clojure code per function
validateur, bouncer, clj-schema (validation)
if code confusing, demand simplification
make temp namespaces explicit: zolo.homeless
domain: business-important logic, not the API, not services, not validation, not talking to the db, just the stuff business people care about; should be pure
if you don’t need it now, don’t build it

liberator, bishop: libraries to help build proper REST APIs in clojure
use the status codes: 1xx – Metadata, 2xx – success, 3xx – redirect, 4xx – client error, 5xx – server error
405: method not allowed
409: conflict
404: resource not present
create returns Location header with location of new resource, in addition to the 201 (created) status code
even better: also return a set of links to related resource (rel = self) and transitions (rel = cancel)
allows client to be loosely coupled from API
client doesn’t need to know how resources move through the system (transition logic)
REST means using multiple URIs, HTTP status codes, and Hypermedia

def’ing refs and atoms at the top level is basically global mutable state via singletons, please avoid
recommend using constructor functions to *return* the state variables you want to use, then pass that state along to each function
easier to test
explicit dependencies
safe to reload when working at the repl
thread-bound state also bad: assumes no lazy sequence returned in function bodies, hides dependencies, and limits caller to using one resource at a time
prefer passing context around to functions
can pull resources out of it
use namespace-qualified keys for isolation
isn’t confined to a single thread
still need to cleanup at the end
more bookkeeping
true constants are fine as global vars (^:const)

alpha release from relevance of open-source libs
use clojure end-to-end to build RIAs
demo: hammock cafe: clojurescript apps communicating to same back-end using datomic store
2 halves: pedestal-service, pedestal-app
ring limits: bound to a single thread’s stack
interceptors: map of functions, has enter and leave for processing requests and responses
can pause and resume along any thread
pushed to be as ring-compatible as possible
use of long polling and server-side events (requests that come in slow and last a long time, get updated as more data comes in)

take things apart
design like bartok (embrace constraints, use harmonic sense)
code like coltrane (constant practice, keep harmonic sense)
build libraries like instruments (design for players, able to be combined with other things)
pursue harmony