1. Time for Functions
@simontcousins

4. let rec qsort = function
| [] -> []
| hd :: tl ->
let lesser, greater = List.partition ((>=) hd) tl
List.concat [qsort lesser; [hd]; qsort greater]
http://rosettacode.org/wiki/Sorting_algorithms/Quicksort#F.23

5. private static List<int> quicksort(List<int> arr)
{
List<int> loe = new List<int>(), gt = new List<int>();
if (arr.Count < 2)
return arr;
int pivot = arr.Count / 2;
int pivot_val = arr[pivot];
arr.RemoveAt(pivot);
foreach (int i in arr)
{
if (i <= pivot_val)
loe.Add(i);
else if (i > pivot_val)
gt.Add(i);
}
List<int> resultSet = new List<int>();
resultSet.AddRange(quicksort(loe));
if (loe.Count == 0){
loe.Add(pivot_val);
}else{
gt.Add(pivot_val);
}
resultSet.AddRange(quicksort(gt));
return resultSet;
}

6. Functional code is…
•
Clear
•
•
Concise
•
•
closer to a statement of the algorithm
less noise and accidental complexity
Correct
•
the type system works with the developer

7. and this
is a
really bi
g but
but…
http://xkcd.com/

8. Some new things to learn…
recursion
pure functions
immutable data
partial application
let rec qsort = function
| [] -> []
| hd :: tl ->
let lesser, greater = List.partition ((>=) hd) tl
List.concat [qsort lesser; [hd]; qsort greater]
pattern matching
higher-order functions
type inference
generics by default
'a list -> 'a list when 'a : comparison

9. let rec qsort = function
| [] -> []
| hd :: tl ->
let lesser, greater = List.partition ((>=) hd) tl
List.concat [qsort lesser; [hd]; qsort greater]
gotcha!

10. Some real-world concerns…
•
Good for demos but what about large
programs?
•
Good for academics but what about us?
•
Elegant code but what about performance?
•
Does it work with legacy software?
•
Where do I find functional programmers?

12. Bespoke Enterprise Applications
for the Energy Sector
•
lots of data
•
forecasts
•
•
•
metered data
market data
lots of types
•
units of measure
•
lots of computations
•
schedules
•
contracts
•
analysis
rates
•
•
station parameters
… all changing over time

13. stay at 50Hz
by
adjusting
these
to make
this zero
{
www.statnett.no
THE
ENERGY
SECTOR

14. Project: Balancing Services
•
Blackstart
•
BMSU
•
Faststart
•
Frequency Response
•
Reactive Power
•
STOR
contracted services
provided by energy
companies to
ensure the security
and stability of
supply
http://www2.nationalgrid.com/uk/services/balancing-services/

15. Old System
New System
•
C#
•
F#
•
OO / Imperative
•
Functional / OO / Imperative
•
Relational Database
•
Document Store
•
Untestable
•
Highly testable
•
Slow
•
Fast
•
Contracts not fully implemented
•
Contracts fully implemented
defeated by complexity
tinyurl.com/stor-contract

16. Dynamic
API
Market
API
Test
Console
Contract
Evaluation
Job API
Asset
API
Contract
Evaluation
API
Scheduler
Document
Store
Web UI
View Model
API

18. Elegant
beautiful
simple
efficient
functional

19. Not Elegant
“… but hey, it’s object-oriented!”

20. Real-world OO
•
Struggles to be elegant
•
top down designs
•
•
high ceremony
•
•
coarse abstractions
data and behaviour tightly coupled
Mutating state is a powerful and dangerous
technique
•
hard to reason about
•
requires synchronised access
Lots of accidental complexity
•
abstraction event horizon
•
•
•
ORMs, IoCs, Mocks, Design Patterns,
UML …
Hard to find developers who have mastered
all of this

21. me
preparing
to
mutate
some
state

22. Not-Only SQL
•
most applications do not require the
flexibility a relational schema affords
•
•
applications are written in terms of
aggregates not relational schemas
•
•
as-of
store inputs and outputs
•
avoid accidental
complexity: ORM,
normal form
persist aggregates
making aggregates immutable affords
•
•
separate reporting concerns from
application concerns
what-if, easy test and debug
fits well with
functional
programs

23. JSON Documents
Input
• RunID
• Contract Parameters
• Asset Parameters
• Dynamic Parameters
• Market Parameters
JobRequest
• RunID
• Contract
• Interval
Pure
Function
Contract
Evaluation
API
Scheduler
Contract
Evaluation
Job API
Output
• RunID
• Revenue
• Additional Information
Document
Store
“Pure I/0”
Input
Output

25. Adoption: F#
•
Low risk
•
Runs on CLR and mono
•
Open source
•
Inter-op with legacy software and libraries
•
Back-out to C#

26. Adoption: Developers
•
Self taught
•
Hire good .NET developers, not language x
developers
•
.NET developer cutting F# production code in
a week
•
Functional programmer in a month

27. Adoption: Managers
?

28. Approach
exploratory
DRYer
REPL driven
repeatedly re-factor
test driven documented development

29. Self-host Web API
let config = new HttpSelfHostConfiguration(baseAddress)
config.MapHttpAttributeRoutes()
config.Formatters.JsonFormatter.SerializerSettings <-
JsonSerializerSettings(
PreserveReferencesHandling = PreserveReferencesHandling.None,
Converters =
[|
Json.TupleConverter()
Json.OptionConverter()
Json.ArrayConverter()
Json.ListConverter()
Json.MapTypeConverter()
Json.UnionTypeConverter()
|])
config.DependencyResolver <- new UnityResolver(container)
F# type JSON
converters

30. Topshelf Windows Service
F# working with an
existing
OO framework
HostFactory.Run(fun hc ->
hc.UseLog4Net("log4net.config")
hc.SetServiceName("Job.Api.Host")
hc.SetDisplayName("E.ON Ancillary Services Job API Host")
hc.SetDescription("An API service for Ancillary Services Jobs.")
hc.RunAsNetworkService() |> ignore
hc.Service<ApiService>(fun (s: ServiceConfigurator<ApiService>) ->
s.ConstructUsing(fun (name: string) -> new ApiService(config)) |> ignore
s.WhenStarted(fun (svc: ApiService) ->
jobRequestQueue.Start()
svc.Start()) |> ignore
s.WhenStopped(fun (svc: ApiService) ->
svc.Stop()
jobRequestQueue.Stop())
|> ignore)
|> ignore)

31. Web API Service
an F# class!!!
type ApiService(config: HttpSelfHostConfiguration) =
!
member val Server =
new HttpSelfHostServer(config) with get, set
!
member this.Start() =
this.Server.OpenAsync().Wait()
member this.Stop() =
if this.Server <> null then
this.Server.CloseAsync().Wait()
this.Server.Dispose()

32. Web API Controller
another F# class!!!
type JobController(log: ILog, jobRequestQueue: JobRequestQueue)
inherit ApiController()
!
[<Route("job/ping")>]
member x.Get() =
log.Debug("ping!!!")
"pong"
[<Route("job")>]
member x.Post(request:JobRequest) =
jobRequestQueue.Add(request)

33. agents: the safe way to manage state
Job Queue
let requests = BlockingQueueAgent<JobRequest>(config.JobRequestQueueLength)
!
let workerName (i: int) = String.Format("worker[{0}]", i)
!
let worker (workerName: string) =
async {
while true do
log.DebugFormat("{0} free", workerName)
let! request = requests.AsyncGet()
log.DebugFormat("{0} busy: job {1}", workerName, request.JobId)
run request
}
async, efficient use of threads
!
for i in 1 .. config.JobRequestWorkers do
Async.Start(workerName i |> worker, CancellationToken.Token)
!
requests.Add(request)
scale workers
github.com/fsprojects/fsharpx/blob/master/src/FSharpx.Core/Agents/
BlockingQueueAgent.fs

34. Execute Job
composition of async computations
async {
let! input = buildRequest dataProvider
let! output = sendToCompute input
let result = buildModel input output
do! store result
}
{

35. Post
dispose of resource when done
async {
use! response =
httpClient.PostAsync(uri, toContent request)
|> Async.AwaitTask
return!
response.EnsureSuccessStatusCode().Content.ReadAsStringAsync()
|> Async.AwaitTask
}
F# async works with TPL Tasks

36. API Call
catch exceptions as Choice2Of2
Async.RunSynchronously(
post client config.JobUri request |> Async.Catch,
config.Timeout)
|> Choice.choice
(fun _ -> log.InfoFormat("Executed Job [{0}]", request.JobId))
(fun exn -> log.Error(String.Format("Failed Job [{0}]", request.JobId), exn))
FSharpx
github.com/fsprojects/fsharpx/blob/master/src/FSharpx.Core/
ComputationExpressions/Monad.fs

37. FR Calculation Request
type FrequencyResponseCalculationRequest = {
Interval: Interval.Time.T
InitialState: FRUnitState
ContractParameters: Line.Time.T<ContractParameters>
Instruction: Line.Time.T<Instruction>
Mel: Line.Time.T<float<MW>>
Sel: Line.Time.T<float<MW>>
AdjustedPN: Line.Time.T<float<MW>>
ActualFrequencies: Line.Time.T<float<Hz>>
TargetFrequencies: Line.Time.T<float<Hz>>
MarketPrices: Line.Time.T<float<``£``/(MW h)>>
}
ubiquitous language

38. Ubiquitous Language
[<Measure>]
[<Measure>]
[<Measure>]
[<Measure>]
type
type
type
type
min
hh
h
MW
units of measure
!
type
type
type
type
Interval<'t> = 't * 't
Point<'x,'y> = 'x * 'y
Segment<'x,'y> = Point<'x,'y> * Point<'x,'y>
Line<'x,'y> = Segment<'x,'y> list
all missing concepts from C# solution

39. Ubiquitous Language
(Revised)
segment is an event
module Segment =
!
segment holds a value
over an interval
type T<'x,'y> =
| Instantaneous of Point.T<'x,'y>
| Discrete of IntervalType.T * Interval.T<'x> * 'y
| Continuous of Point.T<'x,'y> * Point.T<'x,'y>
segment between two data points

40. module Units =
!
Units of Measure
[<AutoOpen>]
module UnitNames =
/// a unit of time
[<Measure>] type minute
/// a unit of time
[<Measure>] type halfhour
/// a unit of time
[<Measure>] type hour
/// a unit of active power
[<Measure>] type megawatt
/// a unit of energy
[<Measure>] type poundssterling
/// a unit of frequency
[<Measure>] type hertz
[<AutoOpen>]
module UnitSymbols =
/// a synonym for halfhour, a unit of time
[<Measure>] type min = minute
/// a synonym for halfhour, a unit of time
[<Measure>] type hh = halfhour
/// a synonym for hour, a unit of time
[<Measure>] type h = hour
/// a synonym for megawatt, a unit of power
[<Measure>] type MW = megawatt
/// a synonym for pounds sterling, a unit of currency
[<Measure>] type ``£`` = poundssterling
/// a synonym for hertz, a unit of frequency
[<Measure>] type Hz = hertz
https://github.com/fsharp/fsharp/blob/master/src/fsharp/FSharp.Core/SI.fs

41. Units of Measure
// Conversion constants
let minutePerHalfhour = 30.0<min>/1.0<hh>
let minutePerHour = 60.0<min>/1.0<h>
let halfhourPerMinute = 1.0<hh>/30.0<min>
let halfhourPerHour = 2.0<hh>/1.0<h>
let hourPerMinute = 1.0<h>/60.0<min>
let hourPerHalfhour = 1.0<h>/2.0<hh>
module Minute =
let toHalfhour (a:float<min>) = a * halfhourPerMinute
let toHour (a:float<min>) = a * hourPerMinute
let inline lift a = LanguagePrimitives.FloatWithMeasure<min>(float a)
let liftTimeSpan (t:TimeSpan) = lift t.TotalMinutes

42. Contract Evaluation
to
p
let run interval initialState parameters
actualFrequencies targetFrequencies marketPrices pdtmLine =
let deloadLine = DeloadLineCalculation.run …
let holdingPayments = holdingPayments …
let referencePrices = ReferencePriceCalculation.run …
responseEnergyPayments …
se
cr
et
… but it involves a fold

43. Testing
// Straight forward implementation
!
let rec reverse = function
| [] -> []
| x::xs -> reverse xs @ [x]
!
// Efficient implementation
!
let rec revAcc xs acc =
match xs with
| [] -> acc
| h::t -> revAcc t (h::acc)
!
let rev xs =
match xs with
| [] -> xs
| [_] -> xs
| h1::h2::t -> revAcc t [h2;h1]
!
// Generate random tests to see if they behave the same
!
Check.Quick(fun (xs:int list) -> reverse xs = rev xs)
github.com/fsharp/FsCheck

44. Testing
nice names
open NUnit.Framework
open FsUnit
!
[<TestFixture; Category("Unit")>]
type ``When I run the deload line calculation`` () =
!
[<Test>]
member x.``with empty MEL line and empty PN line then the deload line is correct`` () =
let melLine = Line.empty
let pnLine = Line.empty
let actual = DeloadLineCalculation.run melLine pnLine
let expected : Line.Time.T<float<MW>> = Line.empty
actual |> should equal expected
structural equality for free
github.com/fsharp/FsUnit

46. C#
F#
Two Implementations of the Same Application
400000
30,801
348,430
21,442
Lines of Code
300000
305,566
200000
16,667
163,276
100000
643
56,929
487
53,270
9,359
42,864
3,630
29,080
0
15
3,011
Braces
Blanks
Null Checks
Comments
Useful Code
App Code
Test Code
Total Code

47. … things aren’t looking good for the old
way of doing things

48. Logging LOC

49. Exception Handling LOC

50. Test Code Ratio

51. Performance

52. … and finally say yes to NOOO

53. Manifesto for Not Only Object-Oriented Development!
We are uncovering better ways of developing software by doing
it and helping others do it. Through this work we have come to
value:
!
•
•
•
•
•
0b
ov
Functions and Types over classes
0, er
si
gn 00
Purity over mutability
0,
at
Composition over inheritance
or 0 0
0
Higher-order functions over method dispatch
ie
s!
Options over nulls
10
!
That is, while there is value in the items on the right (except for
nulls), we value the items on the left more.
notonlyoo.org

54. @simontcousins
simontylercousins.net
www.slideshare.net/simontcousins/time-for-functions