ClojureScript: The Good Parts

ClojureScriptClojureScript
The Good PartsThe Good Parts

カマイルカ /laʒenɔʁɛ̃k/カマイルカ /laʒenɔʁɛ̃k/
lagénorhynquelagénorhynque
(defprofile lagénorhynque
:name "Kent OHASHI"
:languages [Clojure Haskell Python Scala
English français Deutsch русский]
:interests [programming language-learning mathematics]
:contributing [github.com/japan-clojurians/clojure-site-ja])

Lisp × JavaScriptLisp × JavaScript

What is ClojureScript?What is ClojureScript?

(CLJS)(CLJS)
compiler for Clojure that targets JavaScript
cf. (JVM/Java), (CLR/C#)
simple and powerful functional Lisp
Clojure ClojureCLR

Use CasesUse Cases
SPA: / , , , etc.
React Native:
Electron
Node.js
AWS Lambda
etc.
Reagent re-frame Rum Om
re-natal

Try CLJS withTry CLJS with LumoLumo
$ npm install -g lumo-cljs
$ lumo
cljs.user=> (defn hello [& {:keys [to]
#_=> :or {to "world"}}]
#_=> (println (str "Hello, " to "!")))
#'cljs.user/hello
cljs.user=> (hello)
Hello, world!
nil
cljs.user=> (hello :to "ClojureScript")
Hello, ClojureScript!
nil

S-expressions (sexp)S-expressions (sexp)
simple rule: (op arg ...)
various kinds of
functions
macros
special forms
structural editing
, , etc.ParEdit Parinfer

Collection LiteralsCollection Literals
cf. function de nition
cljs.user=> '(1 2 3) ; list
(1 2 3)
cljs.user=> [1 2 3] ; vector
[1 2 3]
cljs.user=> #{1 2 3} ; set
#{1 2 3}
cljs.user=> {:a 1 :b 2 :c 3} ; map
{:a 1, :b 2, :c 3}
(defn hello [& {:keys [to]
:or {to "world"}}]
(println (str "Hello, " to "!")))

Lisp MacrosLisp Macros
compile-time metaprogramming
code as data
sexp -> sexp

e.g. for macro (sequence comprehension)
;; ClojureScript
cljs.user=> (for [x (range 10)
#_=> :when (odd? x)]
#_=> (* x x))
(1 9 25 49 81)
cljs.user=> (macroexpand-1
#_=> '(for [x (range 10)
#_=> :when (odd? x)]
#_=> (* x x)))
(cljs.core$macros/let
[iter__9116__auto__
(cljs.core$macros/fn
,,,
# Python
>>> [x ** 2 for x in range(10) if x % 2 != 0]
[1, 9, 25, 49, 81]
-- Haskell
> [x ^ 2 | x <- [0..9], odd x]
[1,9,25,49,81]

REPL-driven DevelopmentREPL-driven Development
Create a ClojureScript project with Leiningen
$ brew install leiningen
$ lein new figwheel cljs-demo # e.g. "figwheel" template
$ cd cljs-demo
$ lein figwheel # or `cider-jack-in-clojurescript` on Emacs

editor-integrated REPL (e.g. Emacs & )CIDER

browser REPL for front-end development

Changes are automatically loaded in the browser

FunctionalFunctional
ProgrammingProgramming

Immutable PersistentImmutable Persistent
CollectionsCollections
no mutations, no side e ects
high performance
ljs.user=> (conj [1 2] 3) ; add an element to vector
[1 2 3]
cljs.user=> (conj '(1 2) 3) ; add an element to list
(3 1 2)
cljs.user=> (conj #{1 2} 3) ; add an element to set
#{1 2 3}
cljs.user=> (assoc {:a 1 :b 2} :c 3) ; add an entry to map
{:a 1, :b 2, :c 3}

Map and SequenceMap and Sequence
as Core Abstractionsas Core Abstractions
maps: get, assoc
sequences: first, rest, cons
lazy sequences
rare to de ne something like classes or algebraic
data types
few data abstractions and many functions

e.g. maps for modelling entities
cljs.user=> (ns geometry.sphere)
nil
geometry.sphere=> (defn surface-area [{::keys [radius]}]
#_=> (* 4 Math/PI (Math/pow radius 2)))
#'geometry.sphere/surface-area
geometry.sphere=> (defn volume [{::keys [radius]}]
#_=> (* 4/3 Math/PI (Math/pow radius 3)))
#'geometry.sphere/volume
geometry.sphere=> #::{:radius 2}
#:geometry.sphere{:radius 2}
geometry.sphere=> (surface-area #::{:radius 2})
50.26548245743669
geometry.sphere=> (volume #::{:radius 2})
33.510321638291124

e.g. typical sequence manipulations
cljs.user=> (defn leibniz [n-terms]
#_=> (->> (iterate #(+ % 2) 1)
#_=> (map / (cycle [1 -1]))
#_=> (take n-terms)
#_=> (apply +)
#_=> (* 4.0)))
#'cljs.user/leibniz
cljs.user=> (leibniz 1000)
3.140592653839794
3.1414926535900345
3.1415826535897198

Data > Functions > MacrosData > Functions > Macros
data-driven/oriented design
examples
libraries: , ,
frameworks: , ,
Honey SQL Hiccup Reagent
Duct Pedestal re-frame

speci cation system
similar to Racket's
cf. gradual typing
e.g. (Typed Clojure)
clojure.specclojure.spec
contract system
core.typed

Common mistakes with maps ...
;; typo in key name
geometry.sphere=> (surface-area #::{:radias 2})
0
;; incorrect value type
geometry.sphere=> (volume #::{:radius "2"})
33.510321638291124

Introduce clojure.spec
geometry.sphere=> (require '[cljs.spec.alpha :as s
#_=> :include-macros true])
nil
geometry.sphere=> (s/def ::radius (s/and number? pos?))
:geometry.sphere/radius
geometry.sphere=> (s/def ::sphere (s/keys :req [::radius]))
:geometry.sphere/sphere
geometry.sphere=> (s/fdef surface-area
#_=> :args (s/cat :sphere ::sphere)
#_=> :ret number?)
geometry.sphere/surface-area
geometry.sphere=> (s/fdef volume
#_=> :args (s/cat :sphere ::sphere)
#_=> :ret number?)
geometry.sphere/volume

Instrument specs
※ add as a dependency (cf. )
geometry.sphere=> (require '[cljs.spec.test.alpha :as stest
#_=> :include-macros true])
nil
geometry.sphere=> (stest/instrument)
[geometry.sphere/surface-area geometry.sphere/volume]
test.check CLJS-1792
# for example
$ lumo -c src:~/.m2/repository/org/clojure/test.check-0.9.0.jar

Spec-instrumented surfacearea function
geometry.sphere=> (surface-area #::{:radius 2})
50.26548245743669
geometry.sphere=> (surface-area #::{:radias 2})
Call to #'geometry.sphere/surface-area did not conform to spec:
In: [0] val: #:geometry.sphere{:radias 2} fails
spec: :geometry.sphere/sphere
at: [:args :sphere]
predicate: (contains? % :geometry.sphere/radius)
:cljs.spec.alpha/spec #object[cljs.spec.alpha.t_cljs$spec$alpha
10508]
:cljs.spec.alpha/value (#:geometry.sphere{:radias 2})
:cljs.spec.alpha/args (#:geometry.sphere{:radias 2})
:cljs.spec.alpha/failure :instrument
,,,

Spec-instrumented volume function
geometry.sphere=> (volume #::{:radius 2})
33.510321638291124
geometry.sphere=> (volume #::{:radius "2"})
Call to #'geometry.sphere/volume did not conform to spec:
In: [0 :geometry.sphere/radius] val: "2" fails
spec: :geometry.sphere/radius
at: [:args :sphere :geometry.sphere/radius]
predicate: number?
:cljs.spec.alpha/spec #object[cljs.spec.alpha.t_cljs$spec$alpha
10508]
:cljs.spec.alpha/value (#:geometry.sphere{:radius "2"})
:cljs.spec.alpha/args (#:geometry.sphere{:radius "2"})
:cljs.spec.alpha/failure :instrument
,,,

Land of Lisp invades JS world!!Land of Lisp invades JS world!!

ClojureScript: The Good Parts

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