path_module.md

Path module

Before we move on to defining views for the rest of the application, let's introduce one more file - Path.fs and insert it before View.fs:

module SuaveMusicStore.Path

type IntPath = PrintfFormat<(int -> string),unit,string,string,int>

let home = "/"

module Store =
    let overview = "/store"
    let browse = "/store/browse"
    let details : IntPath = "/store/details/%d"

The module will contain all valid routes in our application. We'll keep them here in one place, in order to be able to reuse both in App and View modules. Thanks to that, we will minimize the risk of a typo in our View module. We defined a submodule called Store in order to group routes related to one functionality - later in the tutorial we'll have a few more submodules, each of them reflecting a specific set of functionality of the application.

The IntPath type alias that we declared will let us use our routes in conjunction with static-typed Suave routes (pathScan in App module). We don't need to fully understand the signature of this type, for now we can think of it as a route parametrized with integer value. And indeed, we annotated the details route with this type, so that the compiler treats this value specially. We'll see in a moment how we can use details in App and View modules, with the advantage of static typing.

Let's use the routes from Path module in our App:

let webPart = 
    choose [
        path Path.home >>= (OK View.index)
        path Path.Store.overview >>= (OK "Store")
        path Path.Store.browse >>= browse
        pathScan Path.Store.details (fun id -> OK (sprintf "Details %d" id))
    ]

as well as in our View for aHref to home:

divId "header" [
    h1 (aHref Path.home (text "F# Suave Music Store"))
]

Note, that in App module we still benefit from the static typed routes feature that Suave gives us - the id parameter is inferred by the compiler to be of integer type. If you're not familiar with type inference mechanism, you can follow up this link.