purescript-pux-router

The routing module from Pux framework as a standalone library except that the sampleURL interface has been updated to work with the new Web and Effect libraries that replace the old DOM and Eff ones respectively.

Below is a modified version of the Router documentation from the Pux github website:

Routing

In Pux, routing is a set of applicatives for matching URLs to data types, along with a signal for location changes. These are provided by Pux.Router.

URL changes are mapped to an event. A data type for routes is used to contain the matched URL along with parameter and query data.

data Event = PageView Route | Navigate String DOMEvent
 
data Route = Home | Users String | User Int | NotFound

We also need a function that constructs a route event from a url, which we build using routing applicatives and pass to router to return the matched route:

match :: String -> Event
match url = PageView $ fromMaybe NotFound $ router url $
  Home <$ end
  <|>
  Users <$> (lit "users" *> param "sortBy") <* end
  <|>
  Users "name" <$ (lit "users") <* end
  <|>
  User <$> (lit "users" *> int) <* end

Learn applicative basics in Functors, Applicatives, and Monads in Pictures.

Pux.Router provides applicatives lit, str, num, int, bool, param, params, any, and end for mapping url parts to route values.

As you can see above, lit matches a literal string, and its value is ignored. int matches the second part of /users/123 to the integer value of User. end matches the end of the URL. param matches a query parameter, in our case "sortBy". Queries are a bit tricky as they are optional. Therefore end also matches if there is a query present. This means the order of our Users rules is essential. If we had the param less version first, the one with param would never be tried!

Now that we have a function for making a route from a url, we can map it over the url signal provided by sampleURL takes a window history object from purescript-dom and returns a signal of the URL which is updated whenever the popstate event occurs.