Real World F# talk presented at the SDD conference at the Barbican, London in May 2015

1. REAL-WORLD F# Phil Trelford
SDD, 2015

2. F# TAGLINE
F# is a practical, functional-first
language
that lets you write simple code
to solve complex problems

3. CASE STUDY Phil Trelford, @ptrelford
#SDDConf, 2015

4. I am still waiting for the first bug to come
in,
E-On

5. ANALYSIS OF 2 SIMILAR APPS
C#
8 developers peak
5 years
Requirements not met
F#
2 developers peak
< 1 year
Requirements met

6. LINES OF CODE
Implementati
on
C# F#
Braces 56,929 643
Blanks 29,080 3,630
Null Checks 3,011 15
Comments 53,270 487
Useful Code 163,276 16,667
App Code 305,566 21,442
Test Code 42,864 9,359
Total Code 348,430 30,801

7. CODE PATHOGENS
Logging Exception handling

8. SUMMARY
I can fit the whole F# solution in the blank lines of the C# solution
with 7,000 lines to spare.
WTF C#! OMG F#!
I have spent most of my life writing buggy, bloated software that was
impossible to reason about. What was I thinking?

9. LIVE DEMOS Phil Trelford, @ptrelford
#SDDConf, 2015

10. THOUGHTWORKS TECH RADAR
2012
F#
“F# is excellent at concisely
expressing business and domain
logic.”
Languages

11. CURRENCY CONVERSIONS
[<Measure>] type EUR
[<Measure>] type GBP
let rateEurGbp = 0.783M<GBP/EUR>
// Converts amount in EUR to GBP
let euroToPounds (eur:decimal<EUR>) = eur * rateEurGbp

12. UNITS IN CELLS
type formula =
| Neg of formula
| Exp of formula * formula
| ArithmeticOp of
formula * arithmetic * formula
| LogicalOp of
formula * logical * formula
| Num of UnitValue
| Ref of int * int
| Range of int * int * int * int
| Fun of string * formula list

13. UNITS OF MEASURE

14. SQL TYPE PROVIDER

15. AUTOMATING 2048 WITH CANOPY
start firefox
url "http://gabrielecirulli.github.io/2048/
press up
press left
press right
let score = element ".score-container"
printfn "Score %s" score.Text

16. MARIO TUTORIAL

17. FUNCTIONAL C# Phil Trelford, @ptrelford
#SDDConf, 2015

18. FUNCTIONAL C# - MAP/REDUCE
using System;
using System.Collections.Generic;
public class Enumerable
{
public static IEnumerable<TResult> Map<TSource, TResult>(this IEnumerable<TSource> source, Func<TSource, TResult> func)
{
foreach(var item in source)
{
yield return func(item);
}
}
public static TAccumulate Reduce<TSource,TAccumulate>(this IEnumerable<TSource> source, TAccumulate seed, Func<TAccumulate,TSource,TAccumulate> func)
{
var current = seed;
foreach(var item in source)
{
current = func(current, item);
}
return current;
}
}

19. HIGHER ORDER FUNCTIONS – C#
MAP
public static IEnumerable<TResult> Map<TSource, TResult>(this IEnum
{
foreach(var item in source)
{
yield return func(item);
}
}

20. HIGHER ORDER FUNCTIONS – F#
MAP/REDUCE
let map func items =
for item in items do
func item
let reduce func seed items =
let mutable acc = seed
for item in items do
acc <- func acc
acc

21. INTEGRATING F# Phillip Trelford
SDD, 2015

22. F# COMPONENT DESIGN
GUIDELINES

23. C#/F# INTEROP (MOSTLY IT JUST
WORKS)
C# friendly
Classes
Interfaces
Modules
Records
Tuples(*)
F# specific
Discriminated unions
Function arguments
Curried arguments
Option
Async

24. CONTINUOUS INTEGRATION
F# Project - FSharp.Core App.config – Binding Redirect
<?xml version="1.0" encoding="utf-8"?>
<configuration>
<startup>
<supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.0" />
</startup>
<runtime>
<assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
<dependentAssembly>
<assemblyIdentity name="FSharp.Core"
publicKeyToken="b03f5f7f11d50a3a"
culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-4.3.1.0" newVersion="4.3.1.0" />
</dependentAssembly>
</assemblyBinding>
</runtime>
</configuration>

25. RESOURCES Phillip Trelford
SDD, 2015

26. F# Software
Foundation
http://www.fsharp.org
software stacks
trainings teaching F# user groups snippets
mac and linux cross-platform books and
tutorials
F# community open-source
MonoDevelop
contributions research support
consultancy mailing list

27. F# KOANS
[<Koan>]
let SquareEvenNumbersWithPipelineOperator() =
(* In F#, you can use the pipeline operator to get the benefit of
the parens style with the readability of the statement style. *)
let result =
[0..5]
|> List.filter isEven
|> List.map square
AssertEquality result __

28. TRY IT BEFORE YOU BUY IT

29. BUY THE BOOK

30. QUESTIONS?
Twitter
 @ptrelford
Blog
 http://trelford.com/blog
F# eXchange:
 http://tinyurl.com/fsharpex