Introduction to Railway Oriented Programming

Ed Courtenay@edcourtenay

Ed Courtenay

Senior Engineer, Application Reliability Team

Inspiration for this

talk

• Scott Wlaschin

• F# for Fun and Profit -https://fsharpforfunandprofit.com/rop

Agenda

• So what are we talking about?

• F# demos

• How can these principles be applied to non-functional languages?

• C# demo

Always code as if the person who ends up maintaining your code is a violent psychopath who knows where you live.

http://wiki.c2.com/?CodeForTheMaintainer

What is Railway Oriented Programming?• A functional approach to error handling

• A technique for creating pipelines

• Push error handling to where it belongs

• Control flow over exceptions

Func<Doctor, Doctor>

Regenerate

F# Demo

'TInput Happy Path

'TOutput

Single Track Function

'TA 'TB 'TC 'TD

'TInput Happy Path

Sad Path

Result<'TSuccess, 'TFailure>

Switch Function

('a -> Result<'b, 'c>) -> Result<'a, 'b> -> Result<'b, 'c>

switchFunction twoTrackInput output

MapR

esu

lt<T

A, T

C>

Resu

lt<TA, TC

>

Success path

Failure path

TA TB

TC TC

MapR

esu

lt<l

on

g, s

trin

g>R

esult<

DateTim

e, strin

g>

Success path

Failure path

long DateTime

string string

Bind

Success path

Failure path

TA TB

TC TC

C# Demo

Code for this talk

• https://github.com/ecourtenay/ROP

Any Questions?