On Thu, Dec 15, 2011 at 1:54 PM, Alan Malloy <a...@malloys.org> wrote:
> This will print all the debug information at compile time, which is
> usually not what you want. I have a little macro I use called ?, which
> looks like:
>
> (defmacro ? [x]
> `(let [x# ~x]
> (prn '~x '~'is x#)
> x#))
>
> You could add file and line information to this fairly simply:
>
> (defmacro ? [x]
> (let [line (:line (meta &form))
> file *file*]
> `(let [x# ~x]
> (println (pr-str '~x) "is" (pr-str x#)
> (str "; (" ~file ":" ~line ")"))
> x#)))
>
> And use it like so:
>
> user> (let [x 10]
> (+ 5 (? x)))
> x is 10 ; (NO_SOURCE_FILE:1)
> 15
You might want to change
(pr-str x#)
to something like
(pr-str
(if (seq? x#)
(let [s (Object.)]
(if (= (nth x# 11 s) s)
x#
(concat (take 10 x#) ['...])))
x#))
which will print sequences longer than ten elements as (1 2 3 4 5 6 7
8 9 10 ...) and prevent infinite seqs from blowing things up. Or more
generally you might want to go through pprint which lets you set
*print-len* and *print-level* to generally control the printing of
very large and/or deeply-nested structures. But that adds a new
dependency that needs to be required anywhere you use the macro ...
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