Monads in Practice

Christophe Marchal | Software Architect

A couple of links

http://francesbagual.net

@toff63

http://github.com/toff63

christophe.marchal@ilegra.com

Disclaimer

Manage complexity with Monad

Study Monads online is hard

Academic talks

Func

tor

Monoids

Monads

Category theory

Category Theory

Function

Monoids

Associative

( 1 + 2 ) + 3 = 1 + ( 2 + 3 )

InitiAl Value

Result stay in the same

category

Monoid Example

Monoid

FunctorThings that can be map over

map

capacityBEHaviour

Functor: Example

Functor: Example

Monads

Problem it solves

Scenario

F 1 F 2

sweet

Monads Rules: function to create it

Broken Composition

F 1

F 2

sweet

F 1

map ( f 2 )

sweet

Monads Rules: You need a Functor

Scenario

F 1 F 3

sweet

F 1

sweet

Problem: Nested Monad

map ( f 3 )

sweet

F 1

sweet

Flatmap ( f 3 )

Monads Rules: You need a Flatmap

Business rule

age > 18

AuthorizedNot

Authorized

TRUE False

Business rule implementation

What we want

Monad (?) Code

Trade-off

More code than before

Better API

Easy to reuse

Potential complexity Managed

Traditional Code

Side Effect

Our method can return either a sequence

either null

Exist?

null ?

Riendutout quelquechose

TRUE False

Encapsulating if null with Option

Creating our OptionBagual

Code with Options

Business code

Side Effect

Our method can return either an option

[sequence] either throw an exception

Try!

Try to

execute

Gremio Inter

Success Failure

Encapsulating try/catch with Try

Encapsulating try/catch with Try

Code with Try

Business code

Connection Handling

No silver bullet

Loan Pattern

Final Code

Conclusion

● NO IFs

● Border cases handled on demand

● More declarative types

● Highlight business code

● Easy to create

● More reusable code

Thank You!

Christophe Marchal | Software Architect