The F# Path to Relaxation by Don Syme Born in a lab, matured in the enterprise, and now fully baked as an open-source, cross-platform, professionally-supported language: the F# journey has always been about reconciling the apparently irreconcilable. Javascript and .NET, Linux and Windows, Functional and Objects, Company and Openness, Android and iOS, Programming and Data, Server and Client - F# finds a way. Come along and take a journey with me through the modern programming landscape and the F# approach to language design, interoperability, tooling and community.

1. | Basel
The F# Path to Relaxation
Language Design, Platforms, Community, Openness
Don Syme, F# Community Contributor, MSR Principal Researcher in
Mobile Tools

6. X Y

7. Functional Interop

10. ✔
✔
✔
✖
Functional Interop

11. X Y

12. Enterprise Openness

13. F# is open, cross-
platform, neutral,
independent
All F# language and
tooling is accepting
contributions
The F# community is
very “self-empowered”
fsharp.org
Xamarin provide F#
tools Android and iOS
The Visual F# Tools are
Microsoft’s
professional tools for
Windows and Azure
Debian, RPM and .NET
Core for Linux/OSX
The F# Compiler
Service powers many
other tools
Fable for F#-to-
Javascript
SAFE for F# fullstack
F# 4.1 now complete!

15. fsharp.github.io

16. github.com/fsharp/fslang-design
github.com/fsharp/fslang-suggestions

17. ✔
✔
✔
✔
✔
✔
https://github.com/fsharp/fslang-design/tree/master/FSharp-4.0

18. ✔
✔
✔
✔
✔
✔
https://github.com/fsharp/fslang-design/tree/master/FSharp-4.1

20. docs.microsoft.com/en-us/dotnet/core/

21. fable.io

22. fsharp.github.io/FSharp.Compiler.Service

24. printfn "hello world"
✓
✓
✓
✓
✓
✓

26. let symbolUses =
symbolUses
|> Array.filter (fun symbolUse -> …)
|> Array.Parallel.map (fun symbolUse -> …)
|> Array.filter (fun … -> …)
|> Array.groupBy (fun … -> …)
|> Array.map (fun … ->….)

28. https://lukemerrett.com/fsharp-domain-modelling/
type Status =
| Online
| Unresponsive of string
| Missing of string
| NotChecked of string
| Ignored

29. https://medium.com/@odytrice Ody Mbegbu
type Value =
| Integer of int64
| String of string
| Date of DateTime
| Data of string
| Bool of bool
| Dict of (string * Value) list
| Array of Value list

32. /// The view function giving updated content for the page
let view model dispatch =
match model.Text with
| [| |] ->
div [] [ div [] [str "Loading..."] ]
| _ ->
div [ ClassName "container" ] [
button [ OnClick (fun _ -> dispatch Faster) ] [ str "Faster" ]
div [ ClassName "theText" ] [ str model.Text.[model.Index] ]
button [ OnClick (fun _ -> dispatch Slower) ] [ str "Slower" ]
div [] [ str (sprintf "Ticks Per Update: %d" model.TicksPerUpdate) ]
]
A functional-reactive
dynamic web view

33. /// The view function giving updated content for the page
let view (model: Model) dispatch =
if model.Pressed then
Xaml.Label(text="I was pressed!")
else
Xaml.Button(text="Press Me!", command=(fun () -> dispatch Pressed))
A functional-reactive mobile
app view

34. type Msg = | Pressed
type Model = { Pressed: bool }
let init() = { Pressed=false }
let update msg model =
match msg with
| Pressed -> { model with Pressed = true }
let view (model: Model) dispatch =
if model.Pressed then
Xaml.abel(text="I was pressed!")
else
Xaml.Button(text="Press Me!", command=(fun () -> dispatch Pressed))
type App () =
inherit Application ()
do Program.run init update view
A full Xamarin mobile app
The messages
The initial model
The update function
The dynamic view
Host+run
github.com/fsprojects/Elmish.XamarinForms/
The model

36. ✔
Enterprise Openness

37. X Y

38. Functional Objects

40. type Vector2D (dx:double, dy:double) =
let d2 = dx*dx+dy*dy
member v.DX = dx
member v.DY = dy
member v.Length = sqrt d2
member v.Scale(k) = Vector2D (dx*k, dy*k)
Inputs to object
construction
Exported properties
Exported method
Object internals

41. Object Interface Types
type IObject =
interface ISimpleObject
abstract Prop1 : type
abstract Meth2 : type -> type
Object Expressions
{ new IObject with
member x.Prop1 = expr
member x.Meth1 args = expr }
{ new Object() with
member x.Prop1 = expr
interface IObject with
member x.Meth1 args = expr
interface IWidget with
member x.Meth1 args = expr }
Constructed Class Types
type ObjectType(args) =
let internalValue = expr
let internalFunction args = expr
let mutable internalState = expr
member x.Prop1 = expr
member x.Meth2 args = expr

44. objects as a single paradigm
overuse of hierarchical classification
large abstractions many holes failure points
declarations expressions
complex inheriting complex

46. ✔
Functional Objects

47. fsharp.org/testimonials

48. 350,000
lines of C# OO
by offshore team
30,000
lines of robust F#, with
parallel +more features
An application to evaluate the revenue due from Balancing Services contracts in
the UK energy industry
http://simontcousins.azurewebsites.net/does-the-language-you-use-make-a-
difference-revisited/

51. Zero
bugs in deployed system
“F# is the safe choice for this project,
any other choice is too risky”
An application to evaluate the revenue due from Balancing Services contracts in the
UK energy industry
http://simontcousins.azurewebsites.net/does-the-language-you-use-make-a-
difference-revisited/

53. X Y

54. Pattern
Matching
Abstraction

59. module BasicPatterns =
let (|Value|_|) (e:FSharpExpr) = ...
let (|Const|_|) (e:FSharpExpr) = ...
let (|TypeLambda|_|) (e:FSharpExpr) = ...
let (|Lambda|_|) (e:FSharpExpr) = ...
let (|Application|_|) (e:FSharpExpr) = ...
let (|IfThenElse|_|) (e:FSharpExpr) = ...
let (|Let|_|) (e:FSharpExpr) = ...
let (|LetRec|_|) (e:FSharpExpr) = ...
let (|NewRecord|_|) (e:FSharpExpr) = ...
let (|NewUnionCase|_|) (e:FSharpExpr) = ...
let (|NewTuple|_|) (e:FSharpExpr) = ...
let (|TupleGet|_|) (e:FSharpExpr) = ...

60. let (|IdentifierNameSyntax|_|) (n: CSharpSyntaxNode) =
match n with
| :? IdentifierNameSyntax as t -> Some(t.CSharpKind(), t.Identifier)
| _ -> None
let (|IdentifierName|_|) (n: CSharpSyntaxNode) =
match n.CSharpKind() with
| SyntaxKind.IdentifierName -> ...
| _ -> None
let (|QualifiedNameSyntax|_|) (n: CSharpSyntaxNode) =
match n with
| :? QualifiedNameSyntax as t -> ...
| _ -> None
let (|QualifiedName|_|) (n: CSharpSyntaxNode) =
match n.CSharpKind() with
| SyntaxKind.QualifiedName -> ...
| _ -> None

61. ✔
Pattern
Matching
Abstraction

62. Code Data

64. 1 2 3 4 5 6 7
2012 2013
6,432 10,537

66. Statically
Typed
Dynamically
Typed
Options
• make statically typed langs more
dynamic
• make dynamically typed langs more
static
• apply moderated static typing much
more broadly

68. http://fsharp.github.io/FSharp.Data/images/csv.gif
http://fsharp.github.io/FSharp.Data/images/wb.gif

69. types
Segoe UI Light

70. 01/06/2018 70

71. 01/06/2018 71

72. 01/06/2018 72

73. 01/06/2018 73

74. 01/06/2018 74

75. 01/06/2018 75

76. 01/06/2018 76

77. 01/06/2018 77

78. 01/06/2018 78

79. 01/06/2018 79

80. integrating internet-scale information services
directly into the program's variable and type space is
probably the most innovative programming language
idea I’ve heard of in a decade

81. ✔ ✔
Code Data

82. X Y

83. Sync Async

84. Numbers
Numbers-
with Units

86. Synthesis from
contradiction is at
the heart of applied
PL design
Opposites come in
all shapes and
flavours
Achieve relaxation
today ☺
Code Data
Functi
onal
Objec
ts
Open
Enter
prise
Sync Async
… …

87. Thank you!!
Questions?