building-routes.md

Building routes

As of version 6 Hop doesn't provide matchers anymore, instead you can use UrlParser.

You build your routes by using union types:

type Route
  = HomeRoute
  | UserRoute Int
  | UserStatusRoute Int
  | NotFoundRoute

Then you need to create matchers for these routes:

import UrlParser exposing ((</>), format, oneOf, int, s)

matchers =
  oneOf [
    UrlParser.format HomeRoute (s "")
  , UrlParser.format UserRoute (s "users" </> int)
  , UrlParser.format UserStatusRoute (s "users" </> int </> s "status")
  ]

These matchers will match:

• "/"
• "users/1"
• "users/1/status"

Order matters

The order of the matchers makes a big difference. See these examples.

Given you have some routes and matchers:

import UrlParser exposing (format, s, parse, int, oneOf, (</>))

type Route  = UserRoute Int | UserEditRoute Int

-- match 'users/1'
userMatcher = format UserRoute (s "users" </> int)

-- match '/uses/1/edit'
userEditMatcher = format UserEditRoute (s "users" </> int </> s "edit")

Incorrect order

matchers = 
    oneOf [userMatcher, userEditMatcher]

parse identity matchers "users/1"
== Ok (UserRoute 1) : Result.Result String Repl.Route

parse identity matchers "users/1/edit"
== Err "The parser worked, but /edit was left over."

The userEditMatcher doesn't even run in this case. The userMatcher fails and stops the flow.

Correct order

matchers = 
    oneOf [userEditMatcher, userMatcher]

parse identity matchers "users/1"
== Ok (UserRoute 1) : Result.Result String Repl.Route

parse identity matchers "users/1/edit"
== Ok (UserEditRoute 1) : Result.Result String Repl.Route

This works as expected, so is important to put the more specific matchers first.