Functional Programming in PHP

FUNCTIONAL PHP
SIMON HOLYWELL
12/02/2014
0

View Slide

WHO?
Lead developer
Mosaic in Brighton
Full service agency
@ on Twitter
Treffynnon
SimonHolywell.com

View Slide

WORK
Web apps
Obligatory CMS!

View Slide

PROJECTS
Maintainer of
ssdeep - and extension
- geo library for PHP
- Node.js bot for GTalk - now defunct :(
Idiorm and Paris
PECL HHVM
Navigator
PHP-at-Job-Queue-Wrapper
njsbot

View Slide

FUNCTIONS IN PHP
Rarely employed
Discouraged by PHP's evolution
Naming collisions
The old name spacing object

View Slide

SIMPLE BEASTS
PHP functions are:
Easy
Contained
Unaware of global state
Can now be namespaced

View Slide

FUNCTION
<
?
p
h
p
f
u
n
c
t
i
o
n h
e
l
l
o
(
$
a
r
g = '
W
o
r
l
d
'
) {
e
c
h
o _
_
F
U
N
C
T
I
O
N
_
_ . " $
a
r
g
"
;
}
h
e
l
l
o
(
)
; /
/ h
e
l
l
o W
o
r
l
d

View Slide

A LITTLE BIT OF HISTORY
I started with PHP3
Functions were the norm
Classes merely wrapped them
OOP was very poorly understood

View Slide

DRY
Most mashed code with HTML
Functions promoted code reuse
HTML then had functions in it!

View Slide

EVOLVE
Come PHP4 you get better OOP
Functions no longer in focus
They become seen poorer cousins
Can't carry context vs. class properties

View Slide

PHP5
Functions are still marginalised
Still seen as spaghetti
The bad way

View Slide

PHP5.3+
Proper anonymous functions
We get closures!

View Slide

THE BASICS ARE IN
PLACE
¡Functional is possible!

View Slide

JUST WHAT IS
FUNCTIONAL?
Programming without assignment
Stateless
Pure

View Slide

WITHOUT ASSIGNMENT...
Say goodbye to
$
v
a
r = '
v
a
l
u
e
'
;
$
C
l
a
s
s
I
n
s
t
a
n
c
e
-
>
p
r
o
p
e
r
t
y = '
v
a
l
u
e
'
;

View Slide

STATELESS AND PURE
No:
Globals
Side effects
Incrementors/accumulators
For, while or foreach loops

View Slide

PASSING VALUES
From function to function as
Arguments
Return values

View Slide

10
How would you sum all the integers from one to ten?

View Slide

IMPERATIVE WAY
<
?
p
h
p
$
s
u
m = 0
;
f
o
r
(
$
i = 1
; $
i <
= 1
0
; $
i
+
+
) {
$
s
u
m +
= $
i
;
}
/
/ $
s
u
m = 5
5

View Slide

FUNCTIONAL WAY
<
?
p
h
p
a
r
r
a
y
_
s
u
m
(
r
a
n
g
e
(
1
, 1
0
)
)
;
More descriptive
Removes state ($
s
u
m
)
Reusable components

View Slide

LIKE WELL-DESIGNED
OOP
Encapsulated
Broken down into small chunks
Reusable

View Slide

CAN IT BE NEATER?
<
?
p
h
p
a
r
r
a
y
_
s
u
m
(
r
a
n
g
e
(
1
, 1
0
)
)
;
Lua - s
=
0
; f
o
r i
=
1
,
1
0 d
o s
=
s
+
i e
n
d
Erlang - l
i
s
t
s
:
s
u
m
(
l
i
s
t
s
:
s
e
q
(
1
, 1
0
)
)
.
Clojure - (
r
e
d
u
c
e + (
r
a
n
g
e (
i
n
c 1
0
)
)
)
Ruby - (
1
.
.
1
0
)
.
i
n
j
e
c
t
(
0
) {
|
s
,
i
| s + i
}
Python - s
u
m
(
r
a
n
g
e
(
1
, 1
0 + 1
)
)
F# - L
i
s
t
.
s
u
m [
1 .
. 1
0
]
Scala - (
1 t
o 1
0
)
.
s
u
m
Haskell - s
u
m
[
1
.
.
1
0
]

View Slide

THE SCALE
Pure - Haskell
Middle ground - Scala and Clojure
Dabbling - PHP and Python
Hopeless - Brainfuck
%

View Slide

HISTORY
Vienna Circle - 1920s
Philosophers
Logic
Can be defined apart from content
Unless experienced or observed = worthless
M! = ethics, metaphysics, religion and aesthetics

View Slide

KURT GÖDEL
Attended Vienna Circle
Ultimately disproved manifesto
Incompleteness theorem - 1931
Some truths cannot be proven

View Slide

FUNCTIONAL HISTORY
Kurt Gödel - recursively calculated functions - 1930s
Haskell Curry - combinatory logic - 1927
Alan Turing - machines calculating from inputs - 1936
Alonzo Church - lambda calculus - 1930s

View Slide

LAMBDA CALCULUS
Mathematical functions - abstraction
Accept functions as parameters
Return other functions
Basis of functional programming

View Slide

COMBINATORY LOGIC
Haskell Curry
Combinatory calculus - 1927
Primitive functions combined to build others
Named after him
Currying
Haskell

View Slide

WORLD WAR II
Vienna/Göttingen unsafe
Great minds move to US or UK
Turing involved in code breaking

View Slide

ACADEMIC
Little activity 'til late 1950s

View Slide

LISP
1958
Jon McCarthy
MIT
Became the standard for AI

View Slide

MOMENTUM
Some advances
Still mostly academic
Imperative programming the norm

View Slide

TELEPHONES
Fault tolerant system
Erlang by Ericsson
1980s

View Slide

ERICSSON
Ericsson
Erlang
Highly symbolic to improve productivity
Lisp and Prolog discounted
Focused on
Reliability
Concurrency

View Slide

HASKELL
Formed by committee
Pure functional language

View Slide

COMMERCIAL ADOPTION
Domain specific languages (DSL)
Type handling
Pattern matching
Fast to build complex parsers
Less code = easier to maintain

View Slide

CASESTUDY
Barclays bank
Functional Payout Framework
Written in Haskell
DSL for mathematicians
Builds trading applications
Functional eased scope creap
^

View Slide

NONE SHALL PASS!
<
?
p
h
p
$
a
l
l
o
w
a
b
l
e
_
i
p
s = a
r
r
a
y
(
'
1
9
2
.
1
6
8
.
0
.
'
,
'
8
.
8
.
8
.
8
'
,
)
;
a
r
r
a
y
_
f
i
l
t
e
r
(
$
a
l
l
o
w
a
b
l
e
_
i
p
s
, f
u
n
c
t
i
o
n
(
$
i
p
) {
r
e
t
u
r
n $
i
p =
=
s
u
b
s
t
r
(
$
_
S
E
R
V
E
R
[
'
R
E
M
O
T
E
_
A
D
D
R
'
]
, 0
, s
t
r
l
e
n
(
$
i
p
)
)
;
}
) ?
: d
i
e
(
'
D
e
n
i
e
d
.
'
)
;

View Slide

ARRAY_FILTER()
<
?
p
h
p
a
r
r
a
y
_
f
i
l
t
e
r
(
$
a
l
l
o
w
a
b
l
e
_
i
p
s
, f
u
n
c
t
i
o
n
(
$
i
p
) {
Takes a list and predicate
"Removes" items when predicate fails
λ or anonymous function
And hey, it's not a loop!

View Slide

THA PREDICATE
<
?
p
h
p
f
u
n
c
t
i
o
n
(
$
i
p
) {
r
e
t
u
r
n $
i
p =
=
s
u
b
s
t
r
(
$
_
S
E
R
V
E
R
[
'
R
E
M
O
T
E
_
A
D
D
R
'
]
, 0
, s
t
r
l
e
n
(
$
i
p
)
)
;
}
IP v.4 addresses
Chops user IP to same length as allowable ($
i
p
)
Compares result for equality

View Slide

KILLER CONDITION
<
?
p
h
p
?
: d
i
e
(
'
D
e
n
i
e
d
.
'
)
;
Empty arrays == false
Terminates application
Ternary shortcut
<
?
p
h
p
e
x
p
r
1 ? e
x
p
r
2 : e
x
p
r
3
;
e
x
p
r
1 ?
: e
x
p
r
3
;

View Slide

WHAT SAY THE BLACK
KNIGHT?
<
?
p
h
p
/
/ $
_
S
E
R
V
E
R
[
'
R
E
M
O
T
E
_
A
D
D
R
'
] = '
1
9
2
.
1
6
8
.
'
$
a
l
l
o
w
a
b
l
e
_
i
p
s = a
r
r
a
y
(
'
1
9
2
.
1
6
8
.
0
.
'
,
'
8
.
8
.
8
.
8
'
,
)
;
a
r
r
a
y
_
f
i
l
t
e
r
(
$
a
l
l
o
w
a
b
l
e
_
i
p
s
, f
u
n
c
t
i
o
n
(
$
i
p
) {
r
e
t
u
r
n $
i
p =
=
s
u
b
s
t
r
(
$
_
S
E
R
V
E
R
[
'
R
E
M
O
T
E
_
A
D
D
R
'
]
, 0
, s
t
r
l
e
n
(
$
i
p
)
)
;
}
) ?
: d
i
e
(
'
D
e
n
i
e
d
.
'
)
;

View Slide

BONUS: ARRAY CLEANER
a
r
r
a
y
_
f
i
l
t
e
r
(
) without a predicate
Entries == false dropped
false == "" == 0 == array() == null == '0' == 0.0
<
?
p
h
p
a
r
r
a
y
_
f
i
l
t
e
r
(
a
r
r
a
y
(
'
'
, '
s
'
, 0
)
)
;
/
/ a
r
r
a
y
(
'
s
'
)

View Slide

BENEFITS OF
FUNCTIONAL
Techniques useful for OOP
Abstraction = more readable
No distracting guff
Just the problem solving stuff

View Slide

...AND MORE
Shorter code = quicker to debug
No global state to assemble in mind
Focus on the hard problems

View Slide

HEY! WAIT THERE'S
STILL MORE
Testing is easier
No globals again
Values are final

View Slide

REFERENTIAL
TRANSPARENCY
Replace any function with it's return value
Algorithm still works!
<
?
p
h
p
a
r
r
a
y
_
s
u
m
(
a
r
r
a
y
(
1
,
2
,
3
,
4
,
5
,
6
,
7
,
8
,
9
,
1
0
)
)
;
/
/ I
s s
t
i
l
l 5
5
!
Can you do that to a for loop?

View Slide

NO!
<
?
p
h
p
$
s
u
m = 0
;
f
o
r
(
$
i = 1
; $
i <
= 1
0
; $
i
+
+
) {
$
s
u
m +
= $
i
;
}
/
/ $
s
u
m = 5
5
Closest:
<
?
p
h
p
$
s
u
m = 0
;
$
s
u
m +
= 1
;
$
s
u
m +
= 2
;
.
.
.
$
s
u
m +
= 1
0
;
/
/ $
s
u
m = 5
5

View Slide

SO WHAT ELSE?
Easier parallel processing
Who's using the other cores in your CPU?
Not common in PHP - see pthreads

View Slide

IF PHP WERE REALLY
FUNCTIONAL
Machine optimisation of code
Lazy-evaluation
Hot code deployment (Erlang!)
%

View Slide

STEP BACK - Λ
λ
lambda function
anonymous function
<
?
p
h
p
$
f
u
n
c
_
n
a
m
e = f
u
n
c
t
i
o
n
(
$
p
a
r
a
m
) {
r
e
t
u
r
n $
p
a
r
a
m
;
}
;

View Slide

SHOULD BE FAMILIAR
<
?
p
h
p
s
p
l
_
a
u
t
o
l
o
a
d
_
r
e
g
i
s
t
e
r
(
f
u
n
c
t
i
o
n (
$
c
l
a
s
s
) {
i
n
c
l
u
d
e '
c
l
a
s
s
e
s
/
' . $
c
l
a
s
s . '
.
c
l
a
s
s
.
p
h
p
'
;
}
)
;
If not - how about in JS:
b
u
t
t
o
n
.
o
n
c
l
i
c
k = f
u
n
c
t
i
o
n
(
) {
a
l
e
r
t
(
'
L
a
m
b
d
a
'
)
;
}
;

View Slide

EXTEND IT - CLOSURE
Just like a lambda
But, with context/data ($
v
a
l
u
e
)
<
?
p
h
p
$
v
a
l
u
e = 5
;
$
f
u
n
c
_
n
a
m
e = f
u
n
c
t
i
o
n
(
$
p
a
r
a
m
) u
s
e (
$
v
a
l
u
e
) {
r
e
t
u
r
n $
p
a
r
a
m + $
v
a
l
u
e
;
}
;
e
c
h
o $
f
u
n
c
_
n
a
m
e
(
3
)
; /
/ 8
Vars can be other closures or lambdas too
No aliasing unfortunately

View Slide

MAP
a
r
r
a
y
_
m
a
p
(
)
Applies function to each element
Returns new array with adjusted elements
<
?
p
h
p
a
r
r
a
y
_
m
a
p
(
f
u
n
c
t
i
o
n
(
$
v
) { r
e
t
u
r
n s
t
r
t
o
u
p
p
e
r
(
+
+
$
v
)
; }
,
$
a
r
r
a
y
)
;
a
r
r
a
y
(
'
o
'
, '
g
'
, '
o
'
) becomes a
r
r
a
y
(
'
P
'
, '
H
'
, '
P
'
)

View Slide

SOCHI MAP IT
1st

View Slide

APPLIED BY A MAP
2nd

View Slide

MORE MAPPING!
3rd

View Slide

REDUCE
a
r
r
a
y
_
r
e
d
u
c
e
(
)
Fold array down to one value
Applies function to each element
<
?
p
h
p
a
r
r
a
y
_
r
e
d
u
c
e
(
$
a
r
r
a
y
,
f
u
n
c
t
i
o
n
(
$
r
e
s
u
l
t
, $
v
) { r
e
t
u
r
n $
r
e
s
u
l
t .
= $
v
; }
)
;
a
r
r
a
y
(
'
o
'
, '
g
'
, '
o
'
) becomes o
g
o

View Slide

REDUCE FIGURES
9 + 6.10 + 7.62 + 6.98 ...

View Slide

FOLDING SCORES
15.10 + 7.62 + 6.98 ...

View Slide

DISAPPOINTMENT
63.10

View Slide

MAP AND REDUCE
Combined to great effect
<
?
p
h
p
$
a = a
r
r
a
y
(
'
o
'
, '
g
'
, '
o
'
)
;
a
r
r
a
y
_
r
e
d
u
c
e
(
a
r
r
a
y
_
m
a
p
(
f
u
n
c
t
i
o
n
(
$
v
) { r
e
t
u
r
n s
t
r
t
o
u
p
p
e
r
(
+
+
$
v
)
; }
, $
a
)
,
f
u
n
c
t
i
o
n
(
$
r
e
s
u
l
t
, $
v
) { r
e
t
u
r
n $
r
e
s
u
l
t .
= $
v
; }
)
;
/
/ P
H
P

View Slide

RECURSION
Just like the meaning of PHP
A function that calls itself
Directly or
Indirectly
Can be used for loops
Loose or forgotten condition = blown stack

View Slide

HEADS OR TAILS
PHP = heads
<
?
p
h
p
f
u
n
c
t
i
o
n h
e
a
d
_
s
u
m
(
$
x
) {
r
e
t
u
r
n (
$
x =
= 1
)
? $
x
: $
x + h
e
a
d
_
s
u
m
(
$
x - 1
)
;
}
h
e
a
d
_
s
u
m
(
1
0
)
; /
/ 5
5
Other languages have optimised tails

View Slide

HIGHER ORDER
FUNCTIONS
Functions that have other functions as
Call parameters
Return values
Can be used to form expressions

View Slide

HIGHER EXAMPLE
<
?
p
h
p
$
d
a
t
a = a
r
r
a
y
(
1
, 2
, 3
, 4
, 5
, 6
, 7
, 8
, 9
, 1
0
)
;
f
u
n
c
t
i
o
n g
e
t
_
a
l
g
o
r
i
t
h
m
(
$
r
a
n
d
_
s
e
e
d
_
f
n
c
) {
r
e
t
u
r
n (
o
d
d
_
e
v
e
n
(
$
r
a
n
d
_
s
e
e
d
_
f
n
c
(
)
)
) ?
f
u
n
c
t
i
o
n
(
$
v
a
l
u
e
) {
r
e
t
u
r
n $
v
a
l
u
e * $
v
a
l
u
e
;
} :
f
u
n
c
t
i
o
n
(
$
v
a
l
u
e
) u
s
e (
$
r
a
n
d
_
s
e
e
d
_
f
n
c
) {
r
e
t
u
r
n (
$
v
a
l
u
e * $
v
a
l
u
e / $
r
a
n
d
_
s
e
e
d
_
f
n
c
(
)
) + 1
0
;
}
;
}
f
u
n
c
t
i
o
n o
d
d
_
e
v
e
n
(
$
v
a
l
u
e
) {
r
e
t
u
r
n (
$
v
a
l
u
e % 2 =
=
= 0
)
;
}
$
r
a
n
d
_
s
e
e
d
_
f
n
c = f
u
n
c
t
i
o
n
(
) { r
e
t
u
r
n r
a
n
d
(
)
; }
;
$
r
e
s
u
l
t
s = a
r
r
a
y
_
m
a
p
(
g
e
t
_
a
l
g
o
r
i
t
h
m
(
$
r
a
n
d
_
s
e
e
d
_
f
n
c
)
, $
d
a
t
a
)
;

View Slide

PARTIAL FUNCTION
APPLICATION
Essentially set defaults
<
?
p
h
p
$
f
i
r
s
t
_
c
h
a
r = f
u
n
c
t
i
o
n
(
$
s
t
r
i
n
g
) {
r
e
t
u
r
n s
u
b
s
t
r
(
$
s
t
r
i
n
g
, 0
, 1
)
;
}
;
Works nicely with a
r
r
a
y
_
m
a
p
(
)
<
?
p
h
p
a
r
r
a
y
_
m
a
p
(
$
f
i
r
s
t
_
c
h
a
r
, a
r
r
a
y
(
'
f
o
o
'
,
'
b
a
r
'
,
'
b
a
z
'
)
)
;
/
/ a
r
r
a
y
(
'
f
'
,
'
b
'
,
'
b
'
)

View Slide

CURRYING
Each parameter becomes a function
More flexible PFA
<
?
p
h
p
$
f
i
r
s
t
_
c
h
a
r = f
u
n
c
t
i
o
n
(
$
s
t
a
r
t
) {
r
e
t
u
r
n f
u
n
c
t
i
o
n
(
$
l
e
n
g
t
h
) u
s
e (
$
s
t
a
r
t
) {
r
e
t
u
r
n f
u
n
c
t
i
o
n
(
$
s
t
r
i
n
g
) u
s
e (
$
s
t
a
r
t
, $
l
e
n
g
t
h
) {
r
e
t
u
r
n s
u
b
s
t
r
(
$
s
t
r
i
n
g
, $
s
t
a
r
t
, $
l
e
n
g
t
h
)
;
}
;
}
;
}
;
$
a = $
f
i
r
s
t
_
c
h
a
r
(
0
)
;
$
b = $
a
(
1
)
;
$
b
(
'
f
o
o
'
)
; /
/ f
$
c = $
a
(
2
)
;
$
c
(
'
f
o
o
'
)
; /
/ f
o

View Slide

MEMOIZATION
Function local cache
<
?
p
h
p
f
u
n
c
t
i
o
n d
e
m
o
(
) {
s
t
a
t
i
c $
_
c
;
i
f
(
i
s
_
n
u
l
l
(
$
_
c
)
) {
$
_
c = g
e
t
_
s
o
m
e
_
e
x
p
e
n
s
i
v
e
_
o
p
e
r
a
t
i
o
n
(
)
;
}
r
e
t
u
r
n $
_
c
;
}
Handy in class methods too!

View Slide

WHEN TO USE
FUNCTIONAL?
Practice
Innate understanding
Turing complete methodology

View Slide

SO MUCH MORE...
Function composition
Tail recursion
Function objects
New language features
Functors
Applicatives
Monads
Event driven programming
Null handling
& more.

View Slide

EXIT()
Functional PHP
Follow @ for tips
Simon Holywell
Follow @
FunctionalPHP
FunctionalPHP.com
Treffynnon
SimonHolywell.com

View Slide

Functional Programming in PHP

Functional Programming in PHP

Simon Holywell

More Decks by Simon Holywell

Other Decks in Programming

Featured

Transcript