On Jul 17, 2:35 am, Nicolas Oury <[email protected]> wrote:
> Hello,
>
> Can this construct handle higher-order functions?
Nope :)
Chouser brought up this point in IRC. It's not even clear what the
syntax would look like.
> (I mean a function with named arguments as an argument to another
> function).
> It seems quite difficult to do a function dependent transformation on
> the call site when the function is unknown.
>
> Best regards,
>
> Nicolas.
>
> On Thu, 2009-07-16 at 18:46 -0700, Mark Addleman wrote:
> > A few days ago, Chouser and I had a discussion on IRC about the
> > viability of named arguments (a la Smalltalk) for Clojure. In clojure-
> > contrib, there is the macro "defnk" which provides this sort of
> > capability, but it's performance characteristics are worse than than
> > normal function call. I wanted to try my hand at a better performing
> > macro and here is what I came up with:
>
> > (defmacro named-call [fn & named-args]
> > (let [named-args-map (apply hash-map named-args)
> > meta-data (eval `^(var ~fn))
> > arg-names (:arg-names meta-data)
> > arg-list (for [arg-key arg-names] (get named-args-map arg-
> > key))]
> > `(~fn ~...@arg-list)))
>
> > It is used on the call site instead of the definition like so:
>
> > (defn subtract [from take] (- from take))
> > (call subtract :from 10 :take 2)
>
> > The macro assumes some meta data on the function variable which
> > describes the argument list keyed by :arg-names like so:
> > (def #^{:arg-names [:from :take]} subtract subtract)
>
> > The macro isn't as sophisticated as I'd like yet. It doesn't deal
> > with multiple function signatures and I'd like a way to define default
> > values. I'd also like it to return useful error messages if the
> > caller's signature is wrong.
>
> > Thanks to Chouser, Rich and others from IRC for helping me with this
> > stuff. Even if the macro isn't all that valuable, I learned a lot
> > about Clojure in the process. If anyone has any suggestions, I'd love
> > to hear them.
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