I think the best is to use maps. It is rarly a good idea to have too many
arguments.
Am 15.06.2012 08:51 schrieb "David Jacobs" <da...@wit.io>:
> TL;DR: I want to know best practices for designing functions with multiple
> optional arguments.
>
> Okay, so I'm working to build machine learning algorithms in Clojure, and
> they tend to need many arguments. Being a long-time Ruby dev, I like to
> provide sensible defaults for almost all potential arguments that the
> functions take. However, there are some parameters that have to be explicit
> (namely, the data).
>
> To alleviate the pain here, I've started to experiment with named
> arguments. So far, I've come up with something like the following:
>
> (defn descend [xs ys & args]
> (let [defaults {:gradient-fn gradient
> :cost-fn cost
> :yield-fn println
> :alpha 0.01
> :iterations 1000
> :thetas (matrix 0 (second (dim xs)) 1)}
> options (merge defaults (apply hash-map args))
> {:keys [gradient-fn cost-fn yield-fn thetas alpha iterations]}
> options]
> (do-the-algorithm-using-locally-bound-vars)))
>
> It's a little wordy and could be extracted into a macro a la defnk (RIP
> clojure.contrib.def), but it works.
>
> However, if I then want to use method delegation for some algorithms, the
> named argument endeavor gets trickier.
>
> Say I have the same function in two namespaces. One is a general gradient
> descent function, and the other is a specific gradient descent function
> whose only role is to curry a named parameter into the general function.
>
> I want to do something like the following:
>
> (defn descend [xs ys & args]
> (optimization/descend xs ys (conj args :cost-fn cost)))
>
> The problem, of course, is that if I want to delegate the args array to
> another function, I have to destructure args first before passing it into
> another function. In fact, if I ever have a delegating function like this
> (where a partial apply isn't good enough), I can't pass args through to the
> delegating function because it's automatically vectorized.
>
> How do I splat vectors into parameter lists? (Should I be passing in
> records/maps instead of named parameters?)
>
> Thanks,
> David
>
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