Javaslang - Functional Sugar For Java

JΛVΛSLΛNGFunctional Sugar For Java

slang (noun ˈslaŋ)
1. language peculiar to a
particular group
2. 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

Classic Exception Handling
try { 
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 Decomposition
Image 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 stuff
public 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 rescue
public 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

THANK YOU!
<david.schmitz@senacor.com> @koenighotze

Javaslang - Functional Sugar For Java

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