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Functional Programming λ

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About Me Pragmatic, Passionate and Polyglot Programmer @tamizhvendan http://blog.tamizhvendan.in www.ajira.tech bit.ly/fsapplied

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May I Know about you?

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Why another Programming Language?

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Problem

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Problem Solution

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Problem Solution

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Origin

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Origin Destination

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Origin Destination

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Origin Destination

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Origin Destination

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Origin Destination

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Origin Destination

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Origin Destination

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Problem

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Problem Solution

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Problem Solution

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Problem Solution C#

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Problem Solution C# F#

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Problem Solution C# F# Java

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Problem Solution C# F# Java js

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Problem Solution C# F# Java js Azure

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Problem Solution C# F# Java js Azure Aws

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Problem Solution C# F# Java js Azure Aws GCE

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Why Functional Programming?

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I’m Convinced! Tell me How to go about it?

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Functional Programming x Model your Domain (Data)

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Functional Programming λx Define functions which operate on your Domain (Data)

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Functional Programming >> >=> >>= << |> Define “System” by composing functions

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POST /message Chat Server CREATE Model Your Domain x

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POST /message Chat Server CREATE Model Your Domain HttpRequest x

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POST /message Chat Server CREATE Model Your Domain HttpRequest Message x

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POST /message Chat Server CREATE Model Your Domain HttpRequest Message Error x

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POST /message Chat Server CREATE Model Your Domain HttpRequest Message Error Result x

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POST /message Chat Server CREATE Model Your Domain HttpRequest Message Error Result HttpResponse x

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POST /message Chat Server CREATE Define functions λx

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POST /message Chat Server CREATE Define functions readRequest :: HttpRequest -> Result λx

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POST /message Chat Server CREATE Define functions readRequest :: HttpRequest -> Result validate :: Message -> Result λx

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POST /message Chat Server CREATE Define functions readRequest :: HttpRequest -> Result validate :: Message -> Result createInDb :: Message -> Result λx

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POST /message Chat Server CREATE Define functions readRequest :: HttpRequest -> Result validate :: Message -> Result createInDb :: Message -> Result writeResponse :: Result -> HttpResponse λx

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POST /message Chat Server CREATE Compose functions

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POST /message Chat Server CREATE Compose functions readRequest

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POST /message Chat Server CREATE Compose functions readRequest >>= createInDb

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POST /message Chat Server CREATE Compose functions readRequest >>= validate >>= createInDb

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POST /message Chat Server CREATE Compose functions readRequest >>= validate >>= createInDb |> writeResponse

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POST /message Chat Server CREATE Compose functions readRequest system :: HttpRequest -> HttpResponse >>= validate >>= createInDb |> writeResponse

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Let’s Apply!

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Libraries & Frameworks For Web Development

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Learn By Synthesis

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Learn By Synthesis http://www.keyword-suggestions.com/

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Learn By Synthesis http://www.keyword-suggestions.com/

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Learn By Synthesis Don’t dissect the frog, build it! http://www.keyword-suggestions.com/

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Learn By Synthesis Don’t dissect the frog, build it! http://www.keyword-suggestions.com/ http://bit.ly/29QAUyp

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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

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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.

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Functional Programming x Model your Domain (Data)

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Model HttpMethod HttpMethod will be one of the following Get, Put, Post, Delete

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type HttpMethod = | Get | Put | Delete | Post

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Model Header Header is a name value pair

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type Header = string * string

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Model Request Request contains HttpMethod, Path, Headers

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type Request = { Path : string Headers : Header list HttpMethod : HttpMethod }

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Model StatusCode StatusCode will be one of the following Ok, NotFound, BadRequest

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type StatusCode = | Ok | BadRequest | NotFound

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Model Response Response contains StatusCode, Headers & Content

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type Response = { Content : string Headers : Header list StatusCode : StatusCode }

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Designing Handlers express.js ASP.NET Web API Message Handler Go Spark Java

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Design For Composition

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Design For Composition x f1 y y f2 z >> x f1 >> f2 z

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Design For Composition x f1 y y f2 z >> x f1 >> f2 z req handler1 res

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Design For Composition x f1 y y f2 z >> x f1 >> f2 z req handler1 res req handler2 res

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Design For Composition x f1 y y f2 z >> x f1 >> f2 z req handler1 res req handler2 res

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Design For Composition x f1 y y f2 z >> x f1 >> f2 z req handler1 res req handler2 res

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Design For Composition x f1 y y f2 z >> x f1 >> f2 z req handler1 res req handler2 res >>

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Design For Composition x f1 y y f2 z >> x f1 >> f2 z req handler1 res req handler2 res >>

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Design For Composition x f1 y y f2 z >> x f1 >> f2 z req handler1 res req handler2 res >>

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Design For Composition x f1 y y f2 z >> x f1 >> f2 z req handler1 res req handler2 res >> x

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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

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Model Context Context contains Request & Response x

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type Context = { Request : Request Response : Response }

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C handler1 C C handler2 C Design For Composition

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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

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Design For Composition

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C handler1 Design For Composition

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C handler1 Design For Composition

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C handler1 Design For Composition C handler2

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C handler1 Design For Composition C handler2 C

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C handler1 Design For Composition C handler2 C C handler3

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C handler1 Design For Composition C handler2 C C handler3 C

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Async POST /message Chat Server CREATE

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Async POST /message Chat Server CREATE OK Chat Server Inserted

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Design For Composition Async Type Option Type

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C handler1 Design For Composition Async Type Option Type

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C handler1 Design For Composition Async Type Option Type

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C handler1 Design For Composition C handler2 Async Type Option Type

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C handler1 Design For Composition C handler2 C Async Type Option Type

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C handler1 Design For Composition C handler2 C handler3 C Async Type Option Type

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C handler1 Design For Composition C handler2 C handler3 C C Async Type Option Type

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Model WebPart WebPart takes a context and asynchronously may return the (modified) context.

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type WebPart = Context -> Async

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Functional Programming λx Define functions which operate on your Domain (Data)

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Combinator Pattern type WebPart = Context -> Async

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Combinator Pattern

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Combinator Pattern The application is a

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Combinator Pattern The application is a list of WebParts

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Combinator Pattern The application is a list of WebParts Combined together

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Combinator Pattern The application is a list of WebParts Combined together in some order

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Combinator Pattern type WebPart = Context -> Async The application is a list of WebParts Combined together in some order

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Combinator Pattern type WebPart = Context -> Async functions that create WebPart The application is a list of WebParts Combined together in some order

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Combinator Pattern type WebPart = Context -> Async functions that create WebPart The application is a list of WebParts Combined together in some order functions that combine WebParts

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Combinators type WebPart = Context -> Async

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Combinators type WebPart = Context -> Async functions that create WebPart

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Combinators type WebPart = Context -> Async functions that create WebPart combinator<‘a> : ‘a -> WebPart

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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

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let OK content ctx = let response = {ctx.Response with StatusCode = Ok Content = content} {ctx with Response = response} |> Some |> async.Return

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Let’s Test

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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

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let NOT_FOUND content ctx = let response = {ctx.Response with StatusCode = NotFound Content = content} {ctx with Response = response} |> Some |> async.Return

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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

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let BAD_REQUEST content ctx = let response = {ctx.Response with StatusCode = BadRequest Content = content} {ctx with Response = response} |> Some |> async.Return

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Let’s Test

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Filters

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C handler1 Filters

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C handler1 Filters

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C handler1 C handler2 Filters

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C handler1 C handler2 C Filters

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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

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let GET ctx = match ctx.Request.HttpMethod = Get with | true -> Some ctx |> async.Return | _ -> None |> async.Return

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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

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let POST ctx = match ctx.Request.HttpMethod = Post with | true -> Some ctx |> async.Return | _ -> None |> async.Return

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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

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let PUT ctx = match ctx.Request.HttpMethod = Put with | true -> Some ctx |> async.Return | _ -> None |> async.Return

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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

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let DELETE ctx = match ctx.Request.HttpMethod = Delete with | true -> Some ctx |> async.Return | _ -> None |> async.Return

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Let’s Test

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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

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let Path path ctx = match ctx.Request.Path = path with | true -> ctx |> Some |> async.Return | _ -> None |> async.Return

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Let’s Test

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Functional Programming >> >=> >>= << |> Define “System” by composing functions

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Function Composition

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Function Composition x f1 y y f2 z >> x f1 >> f2 z

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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

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Function Composition

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Function Composition

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Function Composition None

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Function Composition C None

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Function Composition C Some None

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Function Composition C Some None

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Function Composition Async C Some None

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Function Composition Async C Some None C

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Function Composition Async Async> C Some None C

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Function Composition Async Async> C Some None type WebPart = Context -> Async C

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Function Composition Async Async> C Some None type WebPart = Context -> Async C C WebPart C

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Function Composition Async Async> C Some None type WebPart = Context -> Async C C WebPart C C WebPart

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Function Composition Async Async> C Some None type WebPart = Context -> Async C C WebPart C C WebPart C WebPart C

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Function Composition Async Async> C Some None type WebPart = Context -> Async C C WebPart C C WebPart C WebPart C C WebPart C

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Function Composition Async Async> C Some None type WebPart = Context -> Async C C WebPart C C WebPart C WebPart C C WebPart C C WebPart C

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Function Composition Async Async> C Some None type WebPart = Context -> Async >> C C WebPart C C WebPart C WebPart C C WebPart C C WebPart C

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Function Composition Async Async> C Some None type WebPart = Context -> Async >> C C WebPart C C WebPart C WebPart C C WebPart C C WebPart C

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Async in F# // Async let count = async.Return 5 let count = async {return 5} // Async -> Async let printAsync asyncContent = async { let! content = asyncContent printfn "%d" content } // calling async functions printAsync count |> Async.RunSynchronously

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Async in F# // Async let count = async.Return 5 let count = async {return 5} // Async -> Async let printAsync asyncContent = async { let! content = asyncContent printfn "%d" content } // calling async functions printAsync count |> Async.RunSynchronously

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Async in F# // Async let count = async.Return 5 let count = async {return 5} // Async -> Async let printAsync asyncContent = async { let! content = asyncContent printfn "%d" content } // calling async functions printAsync count |> Async.RunSynchronously

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Async in F# // Async let count = async.Return 5 let count = async {return 5} // Async -> Async let printAsync asyncContent = async { let! content = asyncContent printfn "%d" content } // calling async functions printAsync count |> Async.RunSynchronously

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Async in F# // Async let count = async.Return 5 let count = async {return 5} // Async -> Async let printAsync asyncContent = async { let! content = asyncContent printfn "%d" content } // calling async functions printAsync count |> Async.RunSynchronously

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Async in F# // Async let count = async.Return 5 let count = async {return 5} // Async -> Async let printAsync asyncContent = async { let! content = asyncContent printfn "%d" content } // calling async functions printAsync count |> Async.RunSynchronously

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Async in F# // Async let count = async.Return 5 let count = async {return 5} // Async -> Async let printAsync asyncContent = async { let! content = asyncContent printfn "%d" content } // calling async functions printAsync count |> Async.RunSynchronously C

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Async in F# // Async let count = async.Return 5 let count = async {return 5} // Async -> Async let printAsync asyncContent = async { let! content = asyncContent printfn "%d" content } // calling async functions printAsync count |> Async.RunSynchronously C

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Async in F# // Async let count = async.Return 5 let count = async {return 5} // Async -> Async let printAsync asyncContent = async { let! content = asyncContent printfn "%d" content } // calling async functions printAsync count |> Async.RunSynchronously C C

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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 "" printOption age printOption ageNotGiven

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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 "" printOption age printOption ageNotGiven

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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 "" printOption age printOption ageNotGiven C

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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 "" printOption age printOption ageNotGiven C

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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 "" printOption age printOption ageNotGiven C C

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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 "" printOption age printOption ageNotGiven C C

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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 "" printOption age printOption ageNotGiven C C

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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 "" printOption age printOption ageNotGiven C C

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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 "" printOption age printOption ageNotGiven C C

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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 "" printOption age printOption ageNotGiven C C

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Composing WebParts

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>=> C w1 C C w2 C C w1 Composing WebParts

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>=> C w1 C C w2 C C w1 Composing WebParts

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>=> C w1 C C w2 C C w1 type WebPart = Context -> Async Composing WebParts

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>=> C w1 C C w2 C C w1 type WebPart = Context -> Async Composing WebParts

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>=> C w1 C C w2 C C w1 type WebPart = Context -> Async Composing WebParts OK C C content string -> Context -> Async

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>=> C w1 C C w2 C C w1 type WebPart = Context -> Async Composing WebParts OK C C content string -> Context -> Async function that create WebPart

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>=> C w1 C C w2 C C w1 type WebPart = Context -> Async Composing WebParts OK C C content string -> Context -> Async compose C C w1 w2 WebPart -> WebPart -> Context -> Async function that create WebPart

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>=> C w1 C C w2 C C w1 type WebPart = Context -> Async Composing WebParts OK C C content string -> Context -> Async compose C C w1 w2 WebPart -> WebPart -> Context -> Async function that create WebPart function that combine WebParts

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compose C C w1 w2

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compose C C w1 w2 let compose w1 w2 ctx = async { return Some ctx }

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compose C C w1 w2

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compose C C w1 w2 Let’s go inside compose

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compose C C w1 w2 let compose w1 w2 ctx = async { return Some ctx } Let’s go inside compose

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compose C C w1 w2 let compose w1 w2 ctx = async { return Some ctx } Let’s go inside compose

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compose C C w1 w2 let compose w1 w2 ctx = async { return Some ctx } let! result = w1 ctx Let’s go inside compose

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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

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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

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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

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compose C C w1 w2 C w1 C C

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compose C C w1 w2 let compose w1 w2 ctx = async { let! result = w1 ctx return Some ctx } C w1 C C

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compose C C w1 w2 let compose w1 w2 ctx = async { let! result = w1 ctx return Some ctx } C w1 C C

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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 -> ()

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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

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compose C C w1 w2 C w1 C C C C

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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

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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

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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

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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

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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 }

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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 }

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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

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Define compose Function WebPart -> WebPart -> Context -> Async compose function takes two web parts and compose it together

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compose function is in turn composable! WebPart -> WebPart -> Context -> Async

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compose function is in turn composable! WebPart -> WebPart -> Context -> Async WebPart -> WebPart -> WebPart

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compose function is in turn composable! WebPart -> WebPart -> Context -> Async

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compose function is in turn composable! WebPart -> WebPart -> Context -> Async WebPart -> WebPart -> WebPart

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Introducing Operators >=> let (>=>) = compose

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Let’s Test

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Let’s Choose ! WebPart list -> Context -> Async Choose function takes a list of web parts and returns the first one that matches the request λx

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Let’s Choose ! WebPart list -> Context -> Async Choose function takes a list of web parts and returns the first one that matches the request λx let rec Choose webparts ctx = async { }

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Let’s Choose ! WebPart list -> Context -> Async Choose function takes a list of web parts and returns the first one that matches the request λx let rec Choose webparts ctx = async { }

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Let’s Choose ! WebPart list -> Context -> Async 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 ->

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Let’s Choose ! WebPart list -> Context -> Async 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 ->

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Let’s Choose ! WebPart list -> Context -> Async 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

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Let’s Choose ! WebPart list -> Context -> Async 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

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Let’s Choose ! WebPart list -> Context -> Async 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

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Let’s Choose ! WebPart list -> Context -> Async 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

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Let’s Choose ! WebPart list -> Context -> Async 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

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Let’s Choose ! WebPart list -> Context -> Async 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

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Let’s Choose ! WebPart list -> Context -> Async 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

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Let’s Play!

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