Basic routing

It's time to extend our WebPart to support multiple routes. First, let's extract the WebPart and bind it to an identifier. We can do that by typing: let webPart = OK "Hello World" and using the webPart identifier in our call to function startWebServer: startWebServer defaultConfig webPart. In C#, one would call it "assign webPart to a variable", but in functional world there's really no concept of a variable. Instead, we can "bind" a value to an identifier, which we can reuse later. Value, once bound, can't be mutated during runtime. Now, let's restrict our WebPart, so that the "Hello World" response is sent only at the root path of our application (localhost:8083/ but not localhost:8083/anything): let webPart = path "/" >=> OK "Hello World" path function is defined in Suave.Filters module, thus we need to open it at the beggining of App.fs. Suave.Operators and Suave.Successful modules will also be crucial - let's open them as well.

open Suave.Filters
open Suave.Operators
open Suave.Successful

path is a function of type: string -> WebPart It means that if we give it a string it will return WebPart. Under the hood, the function looks at the incoming request and returns Some if the path matches, and None otherwise. The >=> operator comes also from Suave library. It composes two WebParts into one by first evaluating the WebPart on the left, and applying the WebPart on the right only if the first one returned Some.

Let's move on to configuring a few routes in our application. To achieve that, we can use the choose function, which takes a list of WebParts, and chooses the first one that applies (returns Some), or if none WebPart applies, then choose will also return None:

let webPart = 
    choose [
        path "/" >=> (OK "Home")
        path "/store" >=> (OK "Store")
        path "/store/browse" >=> (OK "Store")
        path "/store/details" >=> (OK "Details")
    ]

startWebServer defaultConfig webPart

GitHub commit: 4105c21e3f1e1aa432de98e0388f71f89b693234

Files changed:

• App.fs (modified)