a taste of core.async with <?

core.cljs

"
Naming conventions:

go - executes code which contains special blocking operations (e.g. <!), returns a channel, throws global uncaught exceptions
<! - reads from channel without any special treatment of returned error values
<? - reads from maybe-channel, if there's an error value - throws it
<?go - the same as go but \"swallows\" exceptions and returns a maybe-channel
<foo/<?foo:
  1) channel/maybe-channel
  2) a function returning a channel (e.g. <?fetch-items)
  3) a function returning a <function
foo</foo<? - function or a macro which takes channel/maybe-channel as input (e.g. all-settle<?)
<cast<?/<?cast< - explicit casts to another channel type without cloning the underlying channel instance
"

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

; Error handling and finally
(a/go
  (start-progress)
  (try
    (do-smt-with-updated-xxx
      (a/<? (api/<?update-xxx-on-server-asynchronously client "/edit-xxx" xxx)))

    (catch js/Error e
      (do-smt-on-error e))

    (finally
      (stop-progress))))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; client API
(defprotocol ClientProtocol
  (<?query [this url params] "GET request."),,,)

(defmacro query
  "Can be run only inside go-blocks. Makes a query, parks and then returns the deserialized response."
  [this url params]
  `(:r (a/<? (app.api/<?query ~this ~url ~params))))

; Production code
; Waiting for several parallel async operations
(a/go
  ; all-settle<? macro runs async operations simultaneously, blocks until all operations are finished.
  ; If all operations succeed then returns a vector of results.
  ; Otherwise, throws an exception containing a list of all results, some of which will be errors.
  (a/all-settle<?
    [(<?fetch-items {:client       client
                     :fetch-url    "/fetch-table-items"
                     :fetch-params {,,,}})

     ; api/query is a macro
     (a/<?go (do-smt-with-xxx (api/query client "/fetch-xxx" {,,,})))
     (a/<?go (do-smt-with-yyy (api/query client "/fetch-yyy" {,,,})))
     (a/<?go (do-smt-with-zzz (api/query client "/fetch-zzz" {,,,})))]))