Clojure macro inside another macro: how to generate string from symbol

Probably the title is not 100% correct, but let me show you the issue:

(defmacro nvp!
  [n width height]
  `(q/defsketch (symbol (str (name '~n) "-viewport" ))
                  :title (name '~n))

In short: there's a macro called defsketch (it's part of the lib quil, but that does not matter). It's signature is basically defsketch [applet-name & options], and it creates something and binds it to a var called applet-name. For some reason, I want to wrap this into another macro that -- among other things -- takes an applet-name parameter, extends that name into applet-name-viewport and passes that to defsketch. I, however, am unable to figure out how to do that correctly (using macroexpand on the code above ((pprint (macroexpand(nvp test-name 500 500))), I get

(def(clojure.core/symbol (clojure.core/str (clojure.core/name 'my-namespace.core/test-name) "-viewport"))
 (quil.applet/applet
 :title (clojure.core/name 'my-namespace.core/test-name)))

(clojure.core/symbol (clojure.core/str (clojure.core/name 'my-namespace.core/test-name) "-viewport") -- this part looks good, but it should be evaluated somehow before passing it to the inner macro...

Solution

You need to unquote the form that generates the new symbol instead of the original symbol itself.

Here is a small example of how to accomplish this using a defn like macro for the inner macro:

(defmacro mydefn
  [name & body]
  `(defn ~name ~@body))

(defmacro defnview
  [n & body]
  `(mydefn ~(symbol (str (name n) "-viewport")) ~@body))

;; OR

(defmacro defnview
  [n & body]
  (let [n (symbol (str (name n) "-viewport"))]
    `(mydefn ~n ~@body)))

Example:

(defnview foo [a] a)
;; => #'user/foo-viewport

(foo-viewport 1)
;; => 1

(macroexpand '(defnview foo [a] a))
;; => (def foo-viewport (clojure.core/fn ([a] a)))