This email just in case any Googler's stumble across this thread searching for
a generalized threading macro (and a happy conclusion to it). Googling for
examples on this macro was very difficult in my experience, so maybe this might
help someone.
As I found out via the "The case for as->> ("as-last")" thread, a generalized
threading macro was apparently introduced in Clojure 1.5: the as-> form:
clojure.core/as->
([expr name & forms])
Macro
Binds name to expr, evaluates the first form in the lexical context
of that binding, then binds name to that result, repeating for each
successive form, returning the result of the last form.
As this tweet demonstrates, here's how it looks:
(as-> "/tmp" x (java.io.File. x) (file-seq x) (filter (memfn
isDirectory) x) (count x))
First 'x' is bound to "/tmp" and a file is made out of it. 'x' is rebound again
to the resulting file and a put through the 'file-seq' function, etc.
- Greg
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On Jul 7, 2010, at 9:02 AM, Laurent PETIT <[email protected]> wrote:
> 2010/7/7 aria42 <[email protected]>:
>> I've needed --> a few times in my code. I don't think I need it as
>> much as just -> or ->>. Most of the time I've needed it is because I
>> or someone else essentially had parameters
>> in the wrong order. Maybe it belongs in contrib along with -?> which
>> I've needed sparingly as well, but have found useful and would've been
>> non-trivial to have conjured.
>
> -?> is particularly suitable when doing lots of java interop. I use it
> quite a lot in my own code in counterclockwise, for example.
>
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