DSL notes from ALT.NET Seattle

frankdsl.fs

// Possible DSLs for Frank

// Pattern matching of some sort
// Can't short-circuit the match when a method isn't supported
// Must have a default handler
// Hard to make sensible DSL
"/users/{id}" Resource<User> (fun method -> 
  match method with 
  | GET id -> {} 
  | POST user -> {}
  | _ -> {})


// direct DSL
// Abstraction breaks when using new methods
Route "/" [
  GET (fun request -> View "Home")
]
let GET f = ("GET", f) // i.e tuples

// custom operator
// Less obvious
let (@=) method hander = (method, handler)
let GET = "GET"
// Route: string -> (string * (request -> async<response>)) list -> ???
Route "/" [
  GET @= Object (fun request -> async { 
    let! all = db.All()
    all
  }) @? Cache.For(10 minutes) // composition
]

// records
// Less obvious, but has intellisense.
// Allows for easier handling of optional values
// Route: string -> RouteRecord list -> ???
Route "/" [
  {GET with Handler=(fun request -> async {})}
  {POST with AntiForgeryValidation=true; Handler=(fun ...)}
]

// function composition
// Have to process each entry (no map)
// Route: string -> (request -> async<response>) list -> ???
Route "/*" [
  "GET" |> Response<User> (fun request -> View "Home")
  "POST" |> Create (fun request -> async { ... })
]

// Maximum composition!
Route "/(?'id'\d+)" [
  GET @= Require.Authorization 
    @+ getParameter("id") |> db.GetById
    @+ toResponse
    @+ Cache.For(10 minutes);
  POST @= toObject<User>
    @+ db.Add
    @+ getIdForUser >> redirectTo
]

// Issue: handling different types of return values
//   return object
//   return object + responsedata (cookies, headers, etc)
//   return responsedata (cookies, headers, content, etc)
// Maybe always return responsdata and have helpers to go from object to responsedata