With this workflow you can write WebParts like this
  let task ctx = asyncOption {
    let! _ = GET ctx
    let! ctx = Writers.setHeader "foo" "bar"
    return ctx
  }

  we can still use the old symbol but now has a new meaning
  let foo ctx = GET ctx >>= OK "hello"

Classic bind (for SuaveTask)

Entry-point for composing the applicative routes of the http application, by iterating the options, applying the context, arg, to the predicate from the list of options, until there's a match/a Some(x) which can be run.

The constant function, which returns its constant, no matter its input. - theorem: identity = (warbler cnst) (warbler cnst) x = cnst x x = fun _ -> x

Left-to-right Kleisli composition (for SuaveTask).

The conditional function that applies f x a if there's a value in d, or otherwise, applies g a, if there is no value in d.

 Inject a webPart

 +------------+                                            +--------------+
 | url "/a"   +----------+                       +---------+   cont1      |
 +------------+          |                       |         +--------------+
                         |                       |
 +-------------+         |       +----------+    |         +--------------+
 |  url "/b"   +---------+-------+ injected +----+---------+  cont2       |
 +-------------+         |       +----------+    |         +--------------+
                         |                       |
 +-------------+         |                       |         +--------------+
 | url "/b"    +---------+                       +---------+  cont3       |
 +-------------+                                           +--------------+

Which bird? A Warbler! Pipe the request through to a bird that can peck at it. Put another way, using 'warbler' lets you look at the first parameter and then make a decision about what thing to return (it's most likely a WebPart you'll be returning). (Remember, WebPart is HttpContext -> Async) where HttpContext is 'a and Async<_> is 'b.