Elm
Latest commit da6f8d3 Dec 23, 2016 @evancz committed on GitHub Merge pull request #26 from drzhbe/custom-parser-example
fix typo: add argument to custom parser example

README.md

URL Parser

This library helps you turn URLs into nicely structured data.

It is designed to be used with elm-lang/navigation to help folks create single-page applications (SPAs) where you manage browser navigation yourself.

Note: This library is meant to serve as a baseline for future URL parsers. For example, it does not handle query parameters and hashes right now. It is more to (1) get folks started using URL parsers and (2) help us gather data on exactly which scenarios people face.

Examples

Here is a simplified REPL session showing a parser in action:

> import UrlParser exposing ((</>), s, int, string, parseHash)

> parseHash (s "blog" </> int) { ... , hash = "#blog/42" }
Just 42

> parseHash (s "blog" </> int) { ... , hash = "#/blog/13" }
Just 13

> parseHash (s "blog" </> int) { ... , hash = "#/blog/hello" }
Nothing

> parseHash (s "search" </> string) { ... , hash = "#search/dogs" }
Just "dogs"

> parseHash (s "search" </> string) { ... , hash = "#/search/13" }
Just "13"

> parseHash (s "search" </> string) { ... , hash = "#/search" }
Nothing

Normally you have to put many of these parsers to handle all possible pages though! The following parser works on URLs like /blog/42 and /search/badger:

import UrlParser exposing (Parser, (</>), s, int, string, map, oneOf, parseHash)

type Route = Blog Int | Search String

route : Parser (Route -> a) a
route =
  oneOf
    [ map Blog (s "blog" </> int)
    , map Search (s "search" </> string)
    ]

-- parseHash route { ... , hash = "#/blog/58" }    == Just (Blog 58)
-- parseHash route { ... , hash = "#/search/cat" } == Just (Search "cat")
-- parseHash route { ... , hash = "#/search/31" }  == Just (Search "31")
-- parseHash route { ... , hash = "#/blog/cat" }   == Nothing
-- parseHash route { ... , hash = "#/blog" }       == Nothing

Notice that we are turning URLs into nice union types, so we can use case expressions to work with them in a nice way.

Check out the examples/ directory of this repo to see this in use with elm-lang/navigation.

Testing

npm install
npm test

Background

I first saw this general idea in Chris Done’s formatting library. Based on that, Noah and I outlined the API you see in this library. Noah then found Rudi Grinberg’s post about type safe routing in OCaml. It was exactly what we were going for. We had even used the names s and (</>) in our draft API! In the end, we ended up using the “final encoding” of the EDSL that had been left as an exercise for the reader. Very fun to work through!