On Nov 4, 11:49 pm, Baishampayan Ghose <[email protected]> wrote:
> On Sat, Nov 5, 2011 at 11:55 AM, Martin DeMello <[email protected]>
> wrote:
> > What's the cleanest way to run a piece of code if any branch of a cond
> > statement succeeded, without relying on the return value of the
> > individual clauses not to be nil?
>
> > For example, if I have the following piece of code that says I can
> > only move left or up
>
> > (cond
> > (= dir :left) (move-left)
> > (= dir :up) (move-up))
>
> > but (move-left) or (move-up) could themselves return nil, is there any
> > nice way to check if one of them was called?
>
> What about something like this -
>
> (cond
> (= dir :left) (move-left)
> (= dir :up) (move-up)
> :else :nok)
>
> Or
>
> (cond
> (= dir :left) [(move-left)]
> (= dir :up) [(move-up)])
Seconded. Though if you can't easily predict what move-left/move-up
might return (ie they might even return :nok) you might need to be
more careful. Use a namespaced keyword like :my-current-ns/didnt-do-
anything, or a gensym (or a fresh Object) for guaranteed uniqueness:
(let [nothing (Object.)
cond-result (case dir :left (move-left) :up (move-up) nothing)]
(if (identical? nothing cond-result)
...))
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