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JΛVΛSLΛNGFunctional Sugar For Java
slang (noun \ˈslaŋ\)1. language peculiar to a
particular group2. a non-standard vocabulary
composed of words and senses characterized primarily by connotations of extreme informality
Functional Progamming?
Side-Effects
Referential Transparency
Thinking in Values
Side-Effects
Exceptions are non-local goto-statements
try { int i = 1/0; } catch (Throwable t) { … } :(
Referential Transparency
Math.random();
Math.max(1, 2);
Pure functions are a Good ThingTm
Side-effect :(
Thinking in Values
Because Rich Hickey is always right
A taste of JΛVΛSLΛNG!
Immutable Collections
The Try Monad
Structural Decomposition
Immutable Collections Image by Douglas Muth, https://flic.kr/p/acFwxG
Mutable Collections
Returning void is a code smell!
interface Collection<E> { … void clear(); } Side-effect :(
Functional Data Structures
Immutable
Persistent
Referential transparent
(and fully integrated with java.util.*)
List<~> t = List.of(withName(“F95”));
List<~> t2 = t.append(withName(“FCK”));
List
F95 /t
List<~> t = List.of(withName(“F95”));
List<~> t2 = t.append(withName(“FCK”));
List
F95 /
FCK
t
t2
List<~> t = List.of(withName(“F95”));
List<~> t2 = t.append(withName(“FCK”));
List
F95 /
FCK
t
t2
The Try Monad
Classic Exception Handlingtry { URL url = new URL(“http://…”); …} catch (MalformedURLException e) { … } catch (IOException e) { … }
Exception Handling as a Monad
Try.of(() -> new URL(“http://…”)) .flatMap( u->Try.of(u::openConnection) ) .flatMap( c->Try.of(c::getInputStream) )…
Recovering from failure
Try.of(() -> new URL(“http://…”)) … .recover( t-> singletonList(t.getMessage()) ) .getOrElse(emptyList());
Structural DecompositionImage by Arend, https://flic.kr/p/pkBe4g
Handling a HTTP response the classic way
if (OK.equals(res.getStatusCode())) { return exchange.getBody(); } else { return emptyList(); }
…now the JΛVΛSLΛNG way
Match(res.getStatusCode()) .of( Case($OK), res.getBody()), Case(API.<HttpStatus>$(), emptyList()) );
Guard Clauses
Match(Option.of("bla")).of( Case(Some( $(v -> v.length()>4)), identity()), Case(Some($()), "other") )
An example from the trenches Image by Shawn Carpenter, https://flic.kr/p/7FMFjC
A taste, classic stuffpublic void reset(IModel<?> model) { MyLadenModel<?, ?> myLadenModel; if (model instanceof IResettableWrapModel) { IResettableWrapModel<?> res = (IResettableWrapModel<?>) model; myLadenModel = (AbstractKontenLadenModel<?, ?>) res.getWrappedModel(); } else if (model instanceof AbstractLadenModel) { myLadenModel = (AbstractLadenModel<?, ?>) model; } else { throw new IllegalArgumentException(“Peng!”); } kontenLadenModel.reset(); }
JΛVΛSLΛNG to the rescuepublic void reset(IModel<?> model) { MyLadenModel<?, ?> myLadenModel = Match(model).of( Case($(instanceOf(IResettableWrapModel.class)), res->res.getWrappedModel()), Case($(instanceOf(AbstractLadenModel.class)), identity()) );
myLadenModel.reset(); }
We can’t cover everything
Collections Seq, Set, Tree…
Functional Sugar Lift, Memoize, Currying
Values Option, Lazy, Future
Extensions Circuit Breaker, Property Test
But wait…what are the drawbacks?
Java’s baroque type-system
Functional Programming…use Clojure
#Collection-lib > #Logging Impl
Do you want to know more?
Javaslang Homepage
http://www.javaslang.io/javaslang-docs/
Mario Fusco, From object oriented to functional domain modeling
http://bit.ly/28Nj1Ut
