I can use memfn to create a clojure function that invokes a java function.
(macroexpand '(memfn startsWith prefix))
=> (fn* ([target2780 prefix] (. target2780 (startsWith prefix))))
((memfn startsWith prefix) "abc" "a")
=> true
memfn
requires that the function name be a symbol. I'm wondering if I can write a macro to invoke an arbitrary method whose name is provided as a string. That is, I'd like to be able to invoke the following:
(def fn-name "startsWith")
=> #'user/fn-name
(macroexpand '(memfn' fn-name "prefix"))
=> (fn* ([target2780 prefix] (. target2780 (startsWith prefix))))
((memfn fn-name "prefix") "abc" "a")
=> true
The only way I can think to do this involves using read-string
.
(defmacro memfn' [fn-name arg-name]
`(memfn ~(read-string fn-name) ~arg-name))
Edit: A version using read-string and eval that actually works the way I want it to.
(defn memfn' [fn-name arg-name]
(eval (read-string (str "(memfn " fn-name " " arg-name ")"))))
Am I missing a fundamental macro building tool to take the string that a symbol references and turn it into a literal without potentially executing code, as read-string
might?
Thanks for any ideas!
There's no way to do this, with or without read-string. Your proposed solution doesn't work. The distinction you're really trying to make is not between string and symbol, but between runtime data and compile-time literals. Macros do not evaluate the arguments they receive, so even if fn-name
is the name of a var whose value is "startsWith"
, memfn
(or your memfn'
macro) will only ever see fn-name
.