On Feb 4, 8:11 pm, Bryce <fiat.mo...@gmail.com> wrote: > I take your point; I've given up trying to actually define a function > with the expression for the moment (I'd imagine it's still possible, > just much trickier than I thought). My intention was to fake operator > overloading. For my purposes it should be enough to evaluate the > expression with substituted functions, which is very easy: > > (defmacro subFuncs [arg1 arg2] > (eval `(replace ~arg1 ~arg2)) > )
I'm not entirely sure I understand what your exact requirements are, but you can resolve most problems without resorting to eval. The easiest way to locally use a different function in place of a pre- existing one is to re-bind its symbol: user=> (+ 1 2) 3 user=> (let [+ (fn [x y] (+ x y 1))] (+ 1 2)) 4 If you need the "replacement" to work across function calls (i.e. dynamically scoped), you could use binding to re-bind the Var that stores the function: user=> (defn add [x y] (+ x y)) #'user/add (user=> (map add [1 2] [3 4]) (4 6) user=> (binding [add (fn [x y] (- x y))] (map add [1 2] [3 4])) (-2 -2) Note that I didn't use the + function directly here since the compiler would have inlined it, rendering the re-binding ineffective. The binding form is also restricted to the current thread, so beware when using things like pmap and future. Now, if your replacement requirements are really exotic and you absolutely want to write a macro, take a look at clojure.walk/prewalk- replace and postwalk-replace. -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
