stuarthalloway

;; I think it would be a mistake to introduce temporal coupling to prevent typos.

;; The example program below lets you identify "missing" keys specs at
;; the time and place of your choosing, and then handle them as you
;; deem appropriate, without imposing those decisions on other
;; users of spec.

(require '[clojure.spec.alpha :as s]
         '[clojure.set :as set])

stuarthalloway

;; Datomic example code

;; demonstrates various update scenarios, using a news database
;; that contains stories, users, and upvotes

;; grab an in memory database
(use '[datomic.api :only (q db) :as d])
(def uri "datomic:mem://foo")
(d/create-database uri)
(def conn (d/connect uri))

stuarthalloway

;; Datomic example code
;;
;; The extent of entity ?x is all datoms that are about ?x.
;; Drop this into your rules.
;;
;; Demonstrates
;;
;; 1. recursive query (extent calls itself)
;; 2. disjunction (different extent bodies are ORed)
;; 3. component attributes (e.g. your arm is a component, your brother isn't)

stuarthalloway

;; Datomic example code
(use '[datomic.api :only (db q) :as d])

;; ?answer binds a scalar
(q '[:find ?answer :in ?answer]
   42)

;; of course you can bind more than one of anything
(q '[:find ?last ?first :in ?last ?first]
   "Doe" "John")

stuarthalloway

;; clojure.spec's missing piece, work in progress
;; this is only halfway done, somebody else will need to do the other 95%

(require
 '[clojure.spec :as s]
 '[clojure.spec.test :as test])

(defn naive-english-explain
  "Copy and paste this into your app. Figure out what it does by
trying it in production."

stuarthalloway

(ns user)

(def app
  "Intenal Helper"
  (fnil conj []))

(defprotocol PathSeq
  (path-seq* [form path] "Helper for path-seq"))

(extend-protocol PathSeq

stuarthalloway

(defn pull-many
  "Pull pattern from each entity in eids in a single eager query.
Returns a seqable of values sorted by:

sort-k            if sort-k non nil
eids order        if no sort-k specified
unsorted          if sort-k is nil"
  ([db pattern eids]
     (let [e->idx (into {} (map-indexed (fn [idx e] [e idx]) eids))]
       (pull-many db pattern #(-> % :db/id e->idx) eids)))

stuarthalloway

;; try this form-by-form at a REPL
(require '[clojure.spec.alpha :as s])

;; create an inline DSL to describe the FizzBuzz world
(defmacro divides-by
  [nm n]
  `(s/def ~nm (s/and pos-int? #(zero? (mod % ~n)))))

;; specify FizzBuzz 
(divides-by ::fizz 3)

stuarthalloway

;; good repro #0: problem statement

;; in n takes (tricks: translate domain words into Datomic words, be precise.)
;; 0. "Two datoms in transaction conflict" move an entity id to a reference entity take 
;; 1. "Retracting an entity and adding an entity"
;; ...
;; 5. "Retracting a unique identity datom and asserting the same identity on another datom causes
;;    "2 datoms in transaction conflict"

;; good repro #1: depend only on Datomic API

stuarthalloway

(defn squuid-created-at
  "Pull the date back out of a squuid. This will be nonsense if the UUID
passed in was not a squuid!"
  [^java.util.UUID uuid]
  (let [secs (bit-shift-right (.getMostSignificantBits uuid) 32)]
    (java.util.Date. (* secs 1000))))