Getting Started in Functional Programming using F#

Solving complex problems with less code is the beauty of functional programming. But for programmers who are coming from imperative or object-oriented programming background, it is very hard to think from a different perspective and follow the design principles of functional programming.

Functional Programming is not as hard as you think. This talk will help you to demystify the perceived complexities of functional programming and empower you to get started in functional programming using F#.

Meetup: http://www.meetup.com/Chennai-Microsoft-Azure-User-Group/events/235035148/

Transcript

1. Functional Programming λ
3. About Me Pragmatic, Passionate and Polyglot Programmer @tamizhvendan http://blog.tamizhvendan.in www.ajira.tech bit.ly/fsapplied
4. May I Know about you?
5. Why another Programming Language?
6. Problem
7. Problem Solution
8. Problem Solution
9. Origin
10. Origin Destination
11. Origin Destination
12. Origin Destination
13. Origin Destination
14. Origin Destination
15. Origin Destination
16. Origin Destination
17. Problem
18. Problem Solution
19. Problem Solution
20. Problem Solution C#
21. Problem Solution C# F#
22. Problem Solution C# F# Java
23. Problem Solution C# F# Java js
24. Problem Solution C# F# Java js Azure
25. Problem Solution C# F# Java js Azure Aws
26. Problem Solution C# F# Java js Azure Aws GCE
27. Why Functional Programming?
30. I’m Convinced! Tell me How to go about it?
31. Functional Programming x Model your Domain (Data)
32. Functional Programming λx Define functions which operate on your Domain (Data)
33. Functional Programming >> >=> >>= << |> Define “System” by composing functions
34. POST /message Chat Server CREATE Model Your Domain x
35. POST /message Chat Server CREATE Model Your Domain HttpRequest x
36. POST /message Chat Server CREATE Model Your Domain HttpRequest Message x
37. POST /message Chat Server CREATE Model Your Domain HttpRequest Message Error x
38. POST /message Chat Server CREATE Model Your Domain HttpRequest Message Error Result<Message,Error> x
39. POST /message Chat Server CREATE Model Your Domain HttpRequest Message Error Result<Message,Error> HttpResponse x
40. POST /message Chat Server CREATE Define functions λx
41. POST /message Chat Server CREATE Define functions readRequest :: HttpRequest -> Result<Message,Error> λx
42. POST /message Chat Server CREATE Define functions readRequest :: HttpRequest -> Result<Message,Error> validate :: Message -> Result<Message,Error> λx
43. POST /message Chat Server CREATE Define functions readRequest :: HttpRequest -> Result<Message,Error> validate :: Message -> Result<Message,Error> createInDb :: Message -> Result<Message,Error> λx
44. POST /message Chat Server CREATE Define functions readRequest :: HttpRequest -> Result<Message,Error> validate :: Message -> Result<Message,Error> createInDb :: Message -> Result<Message,Error> writeResponse :: Result<Message,Error> -> HttpResponse λx
45. POST /message Chat Server CREATE Compose functions
46. POST /message Chat Server CREATE Compose functions readRequest
47. POST /message Chat Server CREATE Compose functions readRequest >>= createInDb
48. POST /message Chat Server CREATE Compose functions readRequest >>= validate >>= createInDb
49. POST /message Chat Server CREATE Compose functions readRequest >>= validate >>= createInDb |> writeResponse
50. POST /message Chat Server CREATE Compose functions readRequest system :: HttpRequest -> HttpResponse >>= validate >>= createInDb |> writeResponse
51. Let’s Apply!
52. Libraries & Frameworks For Web Development
53. Learn By Synthesis
54. Learn By Synthesis http://www.keyword-suggestions.com/
55. Learn By Synthesis http://www.keyword-suggestions.com/
56. Learn By Synthesis Don’t dissect the frog, build it! http://www.keyword-suggestions.com/
57. Learn By Synthesis Don’t dissect the frog, build it! http://www.keyword-suggestions.com/ http://bit.ly/29QAUyp
58. Domain User sends a Request and gets a Response after some time Request contains HttpMethod, Headers & a Resource Path HttpMethod will be any one of Get, Post, Put, Delete Headers is a list of Key Value pairs Path specifies the path of the resource being requested
59. Domain Response contains StatusCode, Headers & Content StatusCode will be any one of Ok, NotFound, BadRequest Headers is a list of Key Value pairs Content represents resource that is requested.
60. Functional Programming x Model your Domain (Data)
61. Model HttpMethod HttpMethod will be one of the following Get, Put, Post, Delete
62. type HttpMethod = | Get | Put | Delete | Post
63. Model Header Header is a name value pair
64. type Header = string * string
65. Model Request Request contains HttpMethod, Path, Headers
66. type Request = { Path : string Headers : Header list HttpMethod : HttpMethod }
67. Model StatusCode StatusCode will be one of the following Ok, NotFound, BadRequest
68. type StatusCode = | Ok | BadRequest | NotFound
69. Model Response Response contains StatusCode, Headers & Content
70. type Response = { Content : string Headers : Header list StatusCode : StatusCode }
71. Designing Handlers express.js ASP.NET Web API Message Handler Go Spark Java
72. Design For Composition
73. Design For Composition x f1 y y f2 z >> x f1 >> f2 z
74. Design For Composition x f1 y y f2 z >> x f1 >> f2 z req handler1 res
75. Design For Composition x f1 y y f2 z >> x f1 >> f2 z req handler1 res req handler2 res
76. Design For Composition x f1 y y f2 z >> x f1 >> f2 z req handler1 res req handler2 res
77. Design For Composition x f1 y y f2 z >> x f1 >> f2 z req handler1 res req handler2 res
78. Design For Composition x f1 y y f2 z >> x f1 >> f2 z req handler1 res req handler2 res >>
79. Design For Composition x f1 y y f2 z >> x f1 >> f2 z req handler1 res req handler2 res >>
80. Design For Composition x f1 y y f2 z >> x f1 >> f2 z req handler1 res req handler2 res >>
81. Design For Composition x f1 y y f2 z >> x f1 >> f2 z req handler1 res req handler2 res >> x
82. Design For Composition x f1 y y f2 z >> x f1 >> f2 z req handler1 res req handler2 res >> x Create a new type containing Request & Response
83. Model Context Context contains Request & Response x
84. type Context = { Request : Request Response : Response }
85. C handler1 C C handler2 C Design For Composition
86. C handler1 C C handler2 C If handler1 handle the req don’t invoke handler2 Choose either one of the handler Invoke handler2 always Design For Composition
87. Design For Composition
88. C handler1 Design For Composition
89. C handler1 Design For Composition
90. C handler1 Design For Composition C handler2
91. C handler1 Design For Composition C handler2 C
92. C handler1 Design For Composition C handler2 C C handler3
93. C handler1 Design For Composition C handler2 C C handler3 C
94. Async POST /message Chat Server CREATE
95. Async POST /message Chat Server CREATE OK Chat Server Inserted
96. Design For Composition Async Type Option Type
97. C handler1 Design For Composition Async Type Option Type
98. C handler1 Design For Composition Async Type Option Type
99. C handler1 Design For Composition C handler2 Async Type Option Type
100. C handler1 Design For Composition C handler2 C Async Type Option Type
101. C handler1 Design For Composition C handler2 C handler3 C Async Type Option Type
102. C handler1 Design For Composition C handler2 C handler3 C C Async Type Option Type
103. Model WebPart WebPart takes a context and asynchronously may return the (modified) context.
104. type WebPart = Context -> Async<Context option>
105. Functional Programming λx Define functions which operate on your Domain (Data)
106. Combinator Pattern type WebPart = Context -> Async<Context option>
107. Combinator Pattern
108. Combinator Pattern The application is a
109. Combinator Pattern The application is a list of WebParts
110. Combinator Pattern The application is a list of WebParts Combined together
111. Combinator Pattern The application is a list of WebParts Combined together in some order
112. Combinator Pattern type WebPart = Context -> Async<Context option> The application is a list of WebParts Combined together in some order
113. Combinator Pattern type WebPart = Context -> Async<Context option> functions that create WebPart The application is a list of WebParts Combined together in some order
114. Combinator Pattern type WebPart = Context -> Async<Context option> functions that create WebPart The application is a list of WebParts Combined together in some order functions that combine WebParts
115. Combinators type WebPart = Context -> Async<Context option>
116. Combinators type WebPart = Context -> Async<Context option> functions that create WebPart
117. Combinators type WebPart = Context -> Async<Context option> functions that create WebPart combinator<‘a> : ‘a -> WebPart
118. Define OK Combinator OK is a combinator that takes a string and returns a WebPart It modifies the Response’s Content field with the string passed and sets its StatusCode field to Ok Then it asynchronously returns the modified context as Optional type string -> WebPart string -> Context -> Async<Context option>
119. let OK content ctx = let response = {ctx.Response with StatusCode = Ok Content = content} {ctx with Response = response} |> Some |> async.Return
120. Let’s Test
121. Define NOT_FOUND Combinator NOT_FOUND is a combinator that takes a string and returns a WebPart It modifies the Response’s Content field with the string passed and sets its StatusCode field to NotFound Then it asynchronously returns the modified context as Optional type string -> WebPart string -> Context -> Async<Context option>
122. let NOT_FOUND content ctx = let response = {ctx.Response with StatusCode = NotFound Content = content} {ctx with Response = response} |> Some |> async.Return
123. Define BAD_REQUEST Combinator BAD_REQUEST is a combinator that takes a string and returns a WebPart It modifies the Response’s Content field with the string passed and sets its StatusCode field to BadRequest Then it asynchronously returns the modified context as Optional type string -> WebPart string -> Context -> Async<Context option>
124. let BAD_REQUEST content ctx = let response = {ctx.Response with StatusCode = BadRequest Content = content} {ctx with Response = response} |> Some |> async.Return
125. Let’s Test
126. Filters
127. C handler1 Filters
128. C handler1 Filters
129. C handler1 C handler2 Filters
130. C handler1 C handler2 C Filters
131. Define GET Filter GET verifies the HttpMethod of the context’s Request It asynchronously returns the context as Optional Type, if it is Get else asynchronously returns None Context -> Async<Context option>
132. let GET ctx = match ctx.Request.HttpMethod = Get with | true -> Some ctx |> async.Return | _ -> None |> async.Return
133. Define POST Filter POST verifies the HttpMethod of the context’s Request It asynchronously returns the context as Optional Type, if it is Post else asynchronously returns None Context -> Async<Context option>
134. let POST ctx = match ctx.Request.HttpMethod = Post with | true -> Some ctx |> async.Return | _ -> None |> async.Return
135. Define PUT Filter PUT verifies the HttpMethod of the context’s Request It asynchronously returns the context as Optional Type, if it is Put else asynchronously returns None Context -> Async<Context option>
136. let PUT ctx = match ctx.Request.HttpMethod = Put with | true -> Some ctx |> async.Return | _ -> None |> async.Return
137. Define DELETE Filter DELETE verifies the HttpMethod of the context’s Request It asynchronously returns the context as Optional Type, if it is Delete else asynchronously returns None Context -> Async<Context option>
138. let DELETE ctx = match ctx.Request.HttpMethod = Delete with | true -> Some ctx |> async.Return | _ -> None |> async.Return
139. Let’s Test
140. Define Path Filter Path takes a string and verifies it for equality with the Path of the context’s Request It asynchronously returns the context as Optional Type, if the path matches else asynchronously returns None string -> Context -> Context option
141. let Path path ctx = match ctx.Request.Path = path with | true -> ctx |> Some |> async.Return | _ -> None |> async.Return
142. Let’s Test
143. Functional Programming >> >=> >>= << |> Define “System” by composing functions
144. Function Composition
145. Function Composition x f1 y y f2 z >> x f1 >> f2 z
146. Function Composition x f1 y y f2 z >> x f1 >> f2 z x f1 y y f2 z >>x f1 >> f2 >> f3 z z f3 a
147. Function Composition
148. Function Composition
149. Function Composition None
150. Function Composition C None
151. Function Composition C Some<C> None
152. Function Composition C Some<C> None
153. Function Composition Async<None> C Some<C> None
154. Function Composition Async<None> C Some<C> None C
155. Function Composition Async<None> Async<Some<C>> C Some<C> None C
156. Function Composition Async<None> Async<Some<C>> C Some<C> None type WebPart = Context -> Async<Context option> C
157. Function Composition Async<None> Async<Some<C>> C Some<C> None type WebPart = Context -> Async<Context option> C C WebPart C
158. Function Composition Async<None> Async<Some<C>> C Some<C> None type WebPart = Context -> Async<Context option> C C WebPart C C WebPart
159. Function Composition Async<None> Async<Some<C>> C Some<C> None type WebPart = Context -> Async<Context option> C C WebPart C C WebPart C WebPart C
160. Function Composition Async<None> Async<Some<C>> C Some<C> None type WebPart = Context -> Async<Context option> C C WebPart C C WebPart C WebPart C C WebPart C
161. Function Composition Async<None> Async<Some<C>> C Some<C> None type WebPart = Context -> Async<Context option> C C WebPart C C WebPart C WebPart C C WebPart C C WebPart C
162. Function Composition Async<None> Async<Some<C>> C Some<C> None type WebPart = Context -> Async<Context option> >> C C WebPart C C WebPart C WebPart C C WebPart C C WebPart C
163. Function Composition Async<None> Async<Some<C>> C Some<C> None type WebPart = Context -> Async<Context option> >> C C WebPart C C WebPart C WebPart C C WebPart C C WebPart C
164. Async in F# // Async<int> let count = async.Return 5 let count = async {return 5} // Async<int> -> Async<uint> let printAsync asyncContent = async { let! content = asyncContent printfn "%d" content } // calling async functions printAsync count |> Async.RunSynchronously
165. Async in F# // Async<int> let count = async.Return 5 let count = async {return 5} // Async<int> -> Async<uint> let printAsync asyncContent = async { let! content = asyncContent printfn "%d" content } // calling async functions printAsync count |> Async.RunSynchronously
166. Async in F# // Async<int> let count = async.Return 5 let count = async {return 5} // Async<int> -> Async<uint> let printAsync asyncContent = async { let! content = asyncContent printfn "%d" content } // calling async functions printAsync count |> Async.RunSynchronously
167. Async in F# // Async<int> let count = async.Return 5 let count = async {return 5} // Async<int> -> Async<uint> let printAsync asyncContent = async { let! content = asyncContent printfn "%d" content } // calling async functions printAsync count |> Async.RunSynchronously
168. Async in F# // Async<int> let count = async.Return 5 let count = async {return 5} // Async<int> -> Async<uint> let printAsync asyncContent = async { let! content = asyncContent printfn "%d" content } // calling async functions printAsync count |> Async.RunSynchronously
169. Async in F# // Async<int> let count = async.Return 5 let count = async {return 5} // Async<int> -> Async<uint> let printAsync asyncContent = async { let! content = asyncContent printfn "%d" content } // calling async functions printAsync count |> Async.RunSynchronously
170. Async in F# // Async<int> let count = async.Return 5 let count = async {return 5} // Async<int> -> Async<uint> let printAsync asyncContent = async { let! content = asyncContent printfn "%d" content } // calling async functions printAsync count |> Async.RunSynchronously C
171. Async in F# // Async<int> let count = async.Return 5 let count = async {return 5} // Async<int> -> Async<uint> let printAsync asyncContent = async { let! content = asyncContent printfn "%d" content } // calling async functions printAsync count |> Async.RunSynchronously C
172. Async in F# // Async<int> let count = async.Return 5 let count = async {return 5} // Async<int> -> Async<uint> let printAsync asyncContent = async { let! content = asyncContent printfn "%d" content } // calling async functions printAsync count |> Async.RunSynchronously C C
173. Option in F# // int option let age = Some 25 let ageNotGiven = None // int option -> unit let printOption value = match value with | Some v -> printfn "%d" v | None -> printfn "<EMPTY>" printOption age printOption ageNotGiven
174. Option in F# // int option let age = Some 25 let ageNotGiven = None // int option -> unit let printOption value = match value with | Some v -> printfn "%d" v | None -> printfn "<EMPTY>" printOption age printOption ageNotGiven
175. Option in F# // int option let age = Some 25 let ageNotGiven = None // int option -> unit let printOption value = match value with | Some v -> printfn "%d" v | None -> printfn "<EMPTY>" printOption age printOption ageNotGiven C
176. Option in F# // int option let age = Some 25 let ageNotGiven = None // int option -> unit let printOption value = match value with | Some v -> printfn "%d" v | None -> printfn "<EMPTY>" printOption age printOption ageNotGiven C
177. Option in F# // int option let age = Some 25 let ageNotGiven = None // int option -> unit let printOption value = match value with | Some v -> printfn "%d" v | None -> printfn "<EMPTY>" printOption age printOption ageNotGiven C C
178. Option in F# // int option let age = Some 25 let ageNotGiven = None // int option -> unit let printOption value = match value with | Some v -> printfn "%d" v | None -> printfn "<EMPTY>" printOption age printOption ageNotGiven C C
179. Option in F# // int option let age = Some 25 let ageNotGiven = None // int option -> unit let printOption value = match value with | Some v -> printfn "%d" v | None -> printfn "<EMPTY>" printOption age printOption ageNotGiven C C
180. Option in F# // int option let age = Some 25 let ageNotGiven = None // int option -> unit let printOption value = match value with | Some v -> printfn "%d" v | None -> printfn "<EMPTY>" printOption age printOption ageNotGiven C C
181. Option in F# // int option let age = Some 25 let ageNotGiven = None // int option -> unit let printOption value = match value with | Some v -> printfn "%d" v | None -> printfn "<EMPTY>" printOption age printOption ageNotGiven C C
182. Option in F# // int option let age = Some 25 let ageNotGiven = None // int option -> unit let printOption value = match value with | Some v -> printfn "%d" v | None -> printfn "<EMPTY>" printOption age printOption ageNotGiven C C
183. Composing WebParts
184. >=> C w1 C C w2 C C w1 Composing WebParts
185. >=> C w1 C C w2 C C w1 Composing WebParts
186. >=> C w1 C C w2 C C w1 type WebPart = Context -> Async<Context option> Composing WebParts
187. >=> C w1 C C w2 C C w1 type WebPart = Context -> Async<Context option> Composing WebParts
188. >=> C w1 C C w2 C C w1 type WebPart = Context -> Async<Context option> Composing WebParts OK C C content string -> Context -> Async<Context option>
189. >=> C w1 C C w2 C C w1 type WebPart = Context -> Async<Context option> Composing WebParts OK C C content string -> Context -> Async<Context option> function that create WebPart
190. >=> C w1 C C w2 C C w1 type WebPart = Context -> Async<Context option> Composing WebParts OK C C content string -> Context -> Async<Context option> compose C C w1 w2 WebPart -> WebPart -> Context -> Async<Context option> function that create WebPart
191. >=> C w1 C C w2 C C w1 type WebPart = Context -> Async<Context option> Composing WebParts OK C C content string -> Context -> Async<Context option> compose C C w1 w2 WebPart -> WebPart -> Context -> Async<Context option> function that create WebPart function that combine WebParts
192. compose C C w1 w2
193. compose C C w1 w2 let compose w1 w2 ctx = async { return Some ctx }
194. compose C C w1 w2
195. compose C C w1 w2 Let’s go inside compose
196. compose C C w1 w2 let compose w1 w2 ctx = async { return Some ctx } Let’s go inside compose
197. compose C C w1 w2 let compose w1 w2 ctx = async { return Some ctx } Let’s go inside compose
198. compose C C w1 w2 let compose w1 w2 ctx = async { return Some ctx } let! result = w1 ctx Let’s go inside compose
199. compose C C w1 w2 let compose w1 w2 ctx = async { return Some ctx } let! result = w1 ctx C w1 C Let’s go inside compose
200. compose C C w1 w2 let compose w1 w2 ctx = async { return Some ctx } let! result = w1 ctx C w1 C Let’s go inside compose
201. compose C C w1 w2 let compose w1 w2 ctx = async { return Some ctx } let! result = w1 ctx C w1 C C Let’s go inside compose
202. compose C C w1 w2 C w1 C C
203. compose C C w1 w2 let compose w1 w2 ctx = async { let! result = w1 ctx return Some ctx } C w1 C C
204. compose C C w1 w2 let compose w1 w2 ctx = async { let! result = w1 ctx return Some ctx } C w1 C C
205. compose C C w1 w2 let compose w1 w2 ctx = async { let! result = w1 ctx return Some ctx } C w1 C C match result with | Some c -> () | None -> ()
206. compose C C w1 w2 let compose w1 w2 ctx = async { let! result = w1 ctx return Some ctx } C w1 C C match result with | Some c -> () | None -> () C C
207. compose C C w1 w2 C w1 C C C C
208. compose C C w1 w2 let compose w1 w2 ctx = async { let! result = w1 ctx match result with | Some c -> | None -> } C w1 C C C C
209. compose C C w1 w2 let compose w1 w2 ctx = async { let! result = w1 ctx match result with | Some c -> | None -> } C w1 C C C C
210. compose C C w1 w2 let compose w1 w2 ctx = async { let! result = w1 ctx match result with | Some c -> | None -> } C w1 C C C C let! result = w2 c return result return None
211. compose C C w1 w2 let compose w1 w2 ctx = async { let! result = w1 ctx match result with | Some c -> | None -> } C w1 C C C C let! result = w2 c return result return None w2 C
212. compose C C w1 w2 let compose w1 w2 ctx = async { let! result = w1 ctx match result with | Some c -> | None -> } C w1 C C C C let! result = w2 c return result return None w2 C let compose w1 w2 ctx = async { let! result = w1 ctx match result with | Some c -> | None -> return None }
213. compose C C w1 w2 let compose w1 w2 ctx = async { let! result = w1 ctx match result with | Some c -> | None -> } C w1 C C C C let! result = w2 c return result return None w2 C let compose w1 w2 ctx = async { let! result = w1 ctx match result with | Some c -> | None -> return None }
214. compose C C w1 w2 let compose w1 w2 ctx = async { let! result = w1 ctx match result with | Some c -> | None -> } C w1 C C C C let! result = w2 c return result return None w2 C let compose w1 w2 ctx = async { let! result = w1 ctx match result with | Some c -> | None -> return None } return! w2 c
215. Define compose Function WebPart -> WebPart -> Context -> Async<Context option> compose function takes two web parts and compose it together
216. compose function is in turn composable! WebPart -> WebPart -> Context -> Async<Context option>
217. compose function is in turn composable! WebPart -> WebPart -> Context -> Async<Context option> WebPart -> WebPart -> WebPart
218. compose function is in turn composable! WebPart -> WebPart -> Context -> Async<Context option>
219. compose function is in turn composable! WebPart -> WebPart -> Context -> Async<Context option> WebPart -> WebPart -> WebPart
220. Introducing Operators >=> let (>=>) = compose
221. Let’s Test
222. Let’s Choose ! WebPart list -> Context -> Async<Context option> Choose function takes a list of web parts and returns the first one that matches the request λx
223. Let’s Choose ! WebPart list -> Context -> Async<Context option> Choose function takes a list of web parts and returns the first one that matches the request λx let rec Choose webparts ctx = async { }
224. Let’s Choose ! WebPart list -> Context -> Async<Context option> Choose function takes a list of web parts and returns the first one that matches the request λx let rec Choose webparts ctx = async { }
225. Let’s Choose ! WebPart list -> Context -> Async<Context option> Choose function takes a list of web parts and returns the first one that matches the request λx let rec Choose webparts ctx = async { } match webparts with | [] -> return None | x :: xs ->
226. Let’s Choose ! WebPart list -> Context -> Async<Context option> Choose function takes a list of web parts and returns the first one that matches the request λx let rec Choose webparts ctx = async { } match webparts with | [] -> return None | x :: xs ->
227. Let’s Choose ! WebPart list -> Context -> Async<Context option> Choose function takes a list of web parts and returns the first one that matches the request λx let rec Choose webparts ctx = async { } match webparts with | [] -> return None | x :: xs -> let! result = x ctx
228. Let’s Choose ! WebPart list -> Context -> Async<Context option> Choose function takes a list of web parts and returns the first one that matches the request λx let rec Choose webparts ctx = async { } match webparts with | [] -> return None | x :: xs -> let! result = x ctx
229. Let’s Choose ! WebPart list -> Context -> Async<Context option> Choose function takes a list of web parts and returns the first one that matches the request λx let rec Choose webparts ctx = async { } match webparts with | [] -> return None | x :: xs -> let! result = x ctx match result with | Some c -> return Some c | None -> return! Choose xs ctx
230. Let’s Choose ! WebPart list -> Context -> Async<Context option> Choose function takes a list of web parts and returns the first one that matches the request λx let rec Choose webparts ctx = async { } match webparts with | [] -> return None | x :: xs -> let! result = x ctx match result with | Some c -> return Some c | None -> return! Choose xs ctx
231. Let’s Choose ! WebPart list -> Context -> Async<Context option> Choose function takes a list of web parts and returns the first one that matches the request λx let rec Choose webparts ctx = async { } match webparts with | [] -> return None | x :: xs -> let! result = x ctx match result with | Some c -> return Some c | None -> return! Choose xs ctx
232. Let’s Choose ! WebPart list -> Context -> Async<Context option> Choose function takes a list of web parts and returns the first one that matches the request λx let rec Choose webparts ctx = async { } match webparts with | [] -> return None | x :: xs -> let! result = x ctx match result with | Some c -> return Some c | None -> return! Choose xs ctx
233. Let’s Choose ! WebPart list -> Context -> Async<Context option> Choose function takes a list of web parts and returns the first one that matches the request λx let rec Choose webparts ctx = async { } match webparts with | [] -> return None | x :: xs -> let! result = x ctx match result with | Some c -> return Some c | None -> return! Choose xs ctx
234. Let’s Play!
235. https://fsharpforfunandprofit.com http://fsharp.org/ bit.ly/fsapplied https://fsharp.tv