Download - Ur Domain Haz Monoids
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Ur Domain Haz Monoids?
Cyrille Martraire - @cyriux
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"My first encounter with FP concepts was from
DDD"
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A matter of Taste
http://rosshirt.blogspot.fr/
The CodeGourmet
(dedicated to @ziobrando)
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FP
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Passionate developer
PARISSince 1999
@cyriuxCyrille Martraire
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Paris Software Craftsmanship Community
http://www.meetup.com/paris-software-craftsmanship/
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TDDBDDDDDLegacy
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WARNINGThe following show features no spectacular stunt, no live coding, only trivial Java code. You can re-create or re-enact at home with no danger.
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a bit personal
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Adopted 2005Still in love
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...
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What do DDD & FP have in common?
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FP = ?
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http://www.jaider.net/archives/609-intro-to-functional-programming/
PURE
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No StateNo War
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So what do DDD & FP
have in common?
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Value Objects................................................................................................. 19
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Learn oneand get the other
one for FREE!
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DDDFP
(OO)
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NICE STYLE
of code
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DDD+FP = ?
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Example PLZ?
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MONOIDZ!
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@cyriux
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ClosureAssociativity
Neutral Element
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only 3 numbers in
programming
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0, 1, MANY
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Monoid:encapsulate
diversity inside
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0, 1, MANY
Neutral Element
Element
Operation
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Battle against complexity
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Encapsulate details (unit...)
→ simple again
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For a given interface I find myself doing often 0, 1, Many
OO FTW!
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0, 1, MANY
NullObject
Implementation(s)
Composite
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Identity Element
= NullObject
VatCalculation.NONE
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Applied often:
→ scalable process
→ can grow to very complex complexity
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Example PLZ!
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Numbersint+int=int
(3+5)+2=3+(5+2)0
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Lists
(.)+(.,.)=(.,.,.) ︎(a ︎)+(b,︎c)=(a ︎, b)+(c) ︎
()
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Strings
"hello"+"world""cy"+"ri"+"lle"
""
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look simplistic;the key to very
complex behavior
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The key to infinite scalability!
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The key to infinite incremental computing!
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Hadoop x Storm
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Composeability
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Monoids ☛ reduce
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Monoids ☛ domain
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Monoids are typical FP
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FP: everything is a value
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Therefore:Monoids are
values!
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VALUEOBJECTS
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ImmutableEquals by value
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Not Anemic
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18°C+ 16°C= 34°C
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returns a new instance
Change -> new instance
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SIDE-EFFECT -free
FUNCTIONS
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Immutability&
Side-effect-free functions!
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Value Object
A DDD patternto import FP-ish
values in OO languages
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“Functional-First” style
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90%“Functional-First” style
Value Objects
(Ok, gut feeling, I did’nt measure)
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Money
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(25, EUR)+
(30, EUR)=
(55, EUR)
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(25, EUR)+
(30, USD)=
exception
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Money
amountcurrencyadd(Money): Money
<<ValueObject>>
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Cashflows (Payments)
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(25, EUR, today)+
(30, EUR, today)=
(55, EUR, today)
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(25, EUR, today)+
(30, EUR, next day)=
exception
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CashFlow
amountcurrencydate
add(CashFlow):CashFlow
<<ValueObject>>
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CLOSURE of
OPERATION
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Cashflows Sequences
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(10, EUR, 20/03)
(30, EUR, 21/03)
(25, EUR, 21/03)
(12, EUR, 22/03)
(10, EUR, 20/03)
(55, EUR, 21/03)
(12, EUR, 22/03)
+
=
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Cashflow Sequence +
Cashflow Sequence =
Cashflow Sequence
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ObjectArithmetics
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This is how domain experts THINK
about itSAY
SKETCH
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Ranges
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[1, 3]Union [2, 4]
= [1, 4]
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[1, 3]Union [2, 4]
= [1, 4] ][
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Predicates
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FilterAND Filter
= Filter
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FilterAND Filter
= Filter
Always
True
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FilterOR
Filter=
Filter
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FilterOR
Filter=
FilterAlways
False
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Grants
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Read, Write, Execute
"most secure wins"
r + w = rw + x = w
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Configuration Maps
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+
=
Color BLUE
Enable TrueTimeout 30 +
=
Color RED
Enable FalseTimeout 25
Desk FX
Color RED
Enable TrueTimeout 25
Desk FX
Default Desk-specific
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+
=
Color BLUE
Enable TrueTimeout 30 +
=
Color RED
Enable FalseTimeout 25
Desk FX
Color RED
Enable TrueTimeout 25
Desk FX
Default Desk-specific
overw
rite
logic
al OR
min
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+
=
Color BLUE
Enable TrueTimeout 30 +
=
Color RED
Enable FalseTimeout 25
Desk FX
Color RED
Enable TrueTimeout 25
Desk FX
Default Desk-specific
overw
rite
logic
al OR
min
Values are monoids too!
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+
=
Color BLUE
Enable TrueTimeout 30 +
=
Neutral Element
Color BLUE
Enable TrueTimeout 30
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+
=
Color BLUE
Enable TrueTimeout 30 +
=Color BLUE
Enable TrueTimeout 30
Value Objects may be
*BIG* object trees!
(DOM)
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Non-Linear Stuff(average, std dev,
K-clustering, barycenters...)
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Average + Average = WRONG
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Average + Average Not Composeable!
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avg = sum / count
avg = sum / count
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avg = sum / count
avg = sum / count+
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avg = sum / count
avg = sum / count+ +
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avg = sum / count
avg = sum / count
avg = sum / count
+
=
+
=
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(sum, count)
(sum, count)
(sum, count)
+
=
Average
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(sum, sum2, count)
(sum, sum2, count)
(sum, sum2, count)
+
=
Std deviation
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Can model as a monoid even non-
linear stuff!
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MOARMATHS
PLZ!
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Monoid several times...
toString(): Stringunion(MailingList): MailingListintersection(MailingList): MailingListnobody(): MailingListeverybody(): MailingList
MailingList
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Space Vectors
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average temperature = t1.add(t2) .scale(1/2)
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returns a new instance
Change -> new instance
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Space Vector
toCelsius(): TemperaturetoFarenheit(): Temperatureadd(Temperature): Temperaturescale(double): Temperature
Temperature
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Why is it useful?
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(10, EUR, 20/03)
(30, EUR, 21/03)
(25, EUR, 21/03)
(12, EUR, 22/03)
(10, EUR, 20/03)
(55, EUR, 21/03)
(12, EUR, 22/03)
+
=
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Cashflow Sequence +
Cashflow Sequence =
Cashflow Sequence
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This is how domain experts THINK
about itSAY
SKETCH
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DECLARATIVE STYLE
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Much less codeMuch less bugs
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// without monoidsPaymentsFees(...)PaymentsFeesWithOptions(...)PaymentsFeesWithInsuranceAndOptions(...)PaymentsFeesWithInsurance(...)NoFeesButInsurance(...)...
// with monoidsfees(...) : Paymentsoptions(...) : Paymentsinsurance(...) : Payments
Payments.add(Payments) : Payments
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side-effect-free
operation
Very easy to test
input output
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Much less stuff to learn
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1 interface to rule them all
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Cashflow Sequence +
Cashflow Sequence =
Cashflow Sequence
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ESTABLISHEDFORMALISMS
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Monoid/Vector Spaces/Cyclic Group
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LiteratureDocumented
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@annotations
@Monoid()intersection(MailingList): MailingList
@NeutralElement("intersection")nobody(): MailingList
MailingList
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LIVINGDOCUMENTATION
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Signal to Noise ratio
http://www.flickr.com/photos/28471130@N07/2666802097
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Signal to Noise Ratio
• SNR ≥ 80 %
• Signal (VO): CashFlow.multiply(), CashFlowSequence.add(), .negate(), truncate(), Money.add(), .times(), .opposite(), Fixing, FinancialProduct, BankHolidays, ReferenceData
• Noise: CashFlowBuilder, CompositeEngine, ProductFactory, BankHolidaysDecorator
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Write code that tells the business
domain stories
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@annotations
@Monoid()intersection(MailingList): MailingList
@NeutralElement("intersection")nobody(): MailingList
MailingList
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Domain-Specific
@Monoid()overlaping(MailingList): MailingList
@NeutralElement("overlaping")nobody(): MailingList
MailingList
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Value Objects have domain-specific
flavors too:
Convention, Policy, Status, Quantity,
Observation...
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- Annotate domain-relevant classes
- Custom Doclet to export Excel-formatted glossary of every domain concept
Glossary from Code
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Sent directly to end customers
Glossary from Code
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SELF-EXPLAINING VALUES
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We Want:Traceability of processing
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No worry!
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Just enrich our types
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Just enrich our types
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Just enrich our types
label field
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Monad-ishNo logging neededEach value stores
its history
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http://stuartcook.files.wordpress.com/2010/11/happy-monkey.jpg
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In Closing
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Invest time:
Learn DDD, and get free FP exposure
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A paradox:
FP influence helps craft better Object-
Oriented code!
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Monoids are good: Eat Them!
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LOOK 4 Ur DOMAIN MONOIDZ!
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Also learn other maths structures
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Wikipedia is your friend!
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DDD+FP=
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http://wadler.blogspot.fr/2008/04/functional-programming-is-beautiful.html
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Taste-Driven Development
TDD
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Questions? Did you try similar things too?
Let’s discuss!
@cyriux
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Follow me @cyriux
Slides: slideshare.net/cyriux
Blog: cyrille.martraire.com
In Paris? Join !
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Merci