Passing expressions to other expressions

[tomconnors]

It wasn't obvious to me how to write code like (post-command :set-color :id 55 :color (.. evt -target -value)) and get an expression like "@post(appendQueryString('/cmd/set-color', ':id', 55, ':color', evt.target.value))", because even if I wrap the js part in ->expr, it's already a string by the time post-command gets it. It seems like treating these expressions as objects rather than strings might make more sense for cases like this. Should the library have something like this?

(defprotocol IJSExpression
  (form [this] "Get clojure form of expression")
  (js   [this] "Get js form of expression"))

(deftype JSExpression [form]
  Object
  (toString [this] (js this))
  IJSExpression
  (form [this] form)
  (js   [this] (->expr ~form)))

(defmacro js-expr [form]
  `(->JSExpression (quote ~form)))


(comment
  (js-expr (+ 5 6)) ;; #object[kc.admin.server.datastar.JSExpression 0x2b3781b9 "(5) + (6)"]
  (str (js-expr (+ 5 6))) ;; "(5) + (6)"
  (js (js-expr (+ 5 6)))  ;; "(5) + (6)"
  (form (js-expr (+ 5 6))) ;; (+ 5 6)
  )

;; And to demonstrate my use case:
(defn post-command [cmd & params]
  (let [params (map (fn [x]
                      (if (instance? JSExpression x)
                        (form x)
                        (pr-str x)))
                    params)]
    (->expr (@post (appendQueryString ~(str "/cmd/" cmd) ~@params)))))

(comment
  (post-command :set-color) ;; "@post(appendQueryString(\"/cmd/:set-color\"))"
  (post-command :set-color :id 55 :color (js-expr (.. evt -target -value)))
  ;; "@post(appendQueryString(\"/cmd/:set-color\", \":id\", \"55\", \":color\", evt.target.value))"
  )

[Ramblurr]

Wow this is very interesting. Composing expressions is a natural thing to do, I like it.

The only thing that nags me in your example is the mapping over params to either form or pr-str them. Could the lib incorporate that too?

I would also be interested in seeing more example usages of this.