Orthogonal Functional Architecture

Orthogonal Functional
Architecture
Lambda Squared - Knoxville, TN
John A. De Goes — @jdegoes
http://degoes.net

The Dysfunctional Nightmare abandon all
hope ye who
enter

Procedural Code
Ad hoc solutions constructed from large number of non-composable effects that
are reasoned about non-locally.

The Functional Dream bliss awaits all
ye who enter

Functional Code
Principled solutions constructed from a small number of composable building
blocks that are reasoned about locally.

Two Keys to Bliss
Orthogonality + Composability

Two Keys to Bliss
Composability makes functional
code powerful, and
orthogonality makes it
beautiful*
*i.e. modular and uncluttered by irrelevant details.

Two Keys to Bliss
Composable, orthogonal bases
tend to be powerful, but small
and simple to reason about,
permitting flexible, modular
solutions to many problems.

Composability
public interface Future<V> {
boolean cancel(boolean mayInterruptIfRunning);
boolean isDone();
V get() throws InterruptedException, ExecutionException;
V get(long timeout, TimeUnit unit) throws
InterruptedException, ExecutionException, TimeoutException;
}
Is this Java Future composable?

Composability
Composability measures the
extent to which values can be
combined with other values to
produce like values

Composability
1 + 1 = 2
Two integers combine to yield another integer.
1 – 1 = 0
Integers are composable with respect to addition/subtraction.

Composability
Non-Composable Composable

Orthogonality
boolean isDone();
}
Is this Java Future orthogonal?

Orthogonality
Orthogonality measures the
extent to which primitive
operations on values have
single, unique concerns

Orthogonality
Addition moves right
Addition/subtraction are orthogonal
Subtraction moves left

Orthogonality
A
A + B B
A
Non-Orthogonal Orthogonal
B

Orthogonality
boolean isDone();
}
Is this orthogonal?

Orthogonality
boolean cancel(
boolean mayInterruptIfRunning);
boolean isDone();
V get() throws
InterruptedException,
ExecutionException;
V get(long timeout, TimeUnit unit)
throws
InterruptedException,
ExecutionException,
TimeoutException;
}
Is this orthogonal?
Timeout
Get
Timeout + Get

Orthogonality
The cardinal sin of
non-orthogonality is the
tangling of separate concerns,
which infects the code base to
destroy modularity.

Steps Toward Orthogonality
1. Make the system composable.

2. Identify the primitive
operations.

3. Identify the unique concerns.

4. Refactor the primitive
operations until each has a
unique concern.

Worked Examples
boolean isDone();
V get(long timeout, TimeUnit unit) throws InterruptedException,ExecutionException,
TimeoutException;
}
Is this orthogonal?

Worked Examples
The curse of non-orthogonality!
// Would like to write:
<A> Future<A> retryUntilSuccess(Future<A> future, Interval spacing) {
// ???
}
// Forced to write:
A retryUntilSuccess(Future<A> future, Interval spacing,
long timeout, TimeUnit unit) {
// ...
}

Worked Examples
Future<Tuple2<Future<V>, Function<Boolean, Future<Unit>>>> fork();
V unsafePerformGet() throws InterruptedException, ExecutionException;
Future<V> timeout(long timeout, TimeUnit unit);
}
Future 2.0: Detangle ‘get’ and ‘timeout’

Worked Examples
Is this orthogonal?
static int compare(
String str1,
String str2,
boolean nullIsLess)

Worked Examples
Is this orthogonal?
NullIsLess +
Comparison
NullIsLess
Comparison
static int compare(
String str1,
String str2,
boolean nullIsLess)

Worked Examples
The curse of non-orthogonality!
List<String> myAlgorithm(List<String> list, boolean nullIsFirst) {
// ...
int c = compare(first, second, nullIsFirst);
// ...
}

enum Ordering { LT, EQ, GT }
interface Ord<A> {
Ordering compare(A l, A r);
}
Worked Examples
1. Define a unit of composition

class StringOrd extends Ord<String> {
public Ordering compare(String l, String r) {
// ...
}
}
Worked Examples
2. Define one dimension (string comparison)

class NullIsLess<A> {
private final Ord<A> ord;
public NullIsLess(Ord<A> ord) {
this.ord = ord;
}
public Ordering compare(A l, A r) {
if (l == null) { if (r == null) return EQ; else return LT; }
else if (r == null) return GT;
else return ord.compare(l, r);
}
}
Worked Examples
3. Define another dimension (null is first)

List<String> myAlgorithm(List<String> list, Ord<String> ord) {
// ...
Ordering c = ord.compare(first, second); // <- Beautiful!!!
// ...
}
Ord<String> ord = new NullIsLess<String>(new StringOrd());
List<String> list2 = myAlgorithm(list, ord);
Worked Examples
4. Compose orthogonal components

Worked Examples
Is this orthogonal?*
data MVar a
putMVar :: MVar a -> a -> IO ()
takeMVar :: MVar a -> IO a
*Thanks to Fabio the fabulous for this example.

Worked Examples
Is this orthogonal?
data MVar a
putMVar :: MVar a -> a -> IO ()
takeMVar :: MVar a -> IO a
Synchronization +
Concurrency
Synchronization
Concurrency

Worked Examples
data IORef a
newtype Expect a = Expect a
modify ::
IORef a -> (a -> a) -> IO Bool
data Promise a
newPromise :: IO (Promise a, a -> IO ())
awaitPromise :: Promise a -> IO a
Synchronization
(IORef)
Concurrency
(Promise)

Worked Examples
*A tiny part of Apache String Utils.

Worked Examples
Is this orthogonal?
?
?

Worked Examples
Is this orthogonal?
data Parser a = Parser (String -> Either String (String, a))
char :: Parser Char
fail :: String -> Parser a
alt :: Parser a -> Parser a -> Parser a
seq :: Parser a -> (a -> Parser b) -> Parser b
pure :: a -> Parser a
map :: (a -> b) -> Parser a -> Parser b

Worked Examples
data Parser a = Parser (String -> Either String (String, a))
char :: Parser Char
*Trick question — or is it?

Worked Examples
Is this orthogonal?
data Parser a = Parser (String -> ...
char :: Parser Char
SequencingMapping
Flattening

Worked Examples
Is this orthogonal?
data Parser a = Parser (String -> ...
char :: Parser Char
join :: Parser (Parser a) -> Parser a
Mapping
Flattening

Summary
1. Functional code is composable and orthogonal, allowing a small set of
principled building blocks to snap together to solve complex problems in
a predictable, reasonable way.
2. Composability measures the combinability of values.
3. Orthogonality measures the singular focus of primitive operations.
4. Refactor to orthogonality to obtain modular clode, uncluttered by
irrelevant details.

Thank You!
Special thanks to Reid, Cameron, Emily, & the wonderful Knoxville FP
community, and the generous sponsor ResultStack!
John A. De Goes — @jdegoes
http://degoes.net

Orthogonal Functional Architecture

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