On 21 March 2016 at 23:47, Arun Sharma <arun.sha...@gmail.com> wrote:
> On Saturday, March 19, 2016 at 5:35:02 PM UTC-7, red...@gmail.com wrote:
>>
>> ->> is a mechanical transformation taking a form (->> x (a ... w))
>> turning it into (a ... w x), and this same mechanical transformation is
>> in place when nested. You example expands in steps like:
>> [..]
>>
>> you can see each step in the expansion results come from applying the
>> exact same transformation (this transformation is exactly the ->>
>> macro). this is the natural result of a recursive style of definition.
>> While it is technically possible to change the behavior to what you are
>> suggesting, but it would require special casing ->> and any derivative
>> of ->>.
>>
>
> Isn't it a function of how the recursive step is written?
>
No, it's a result of how macros are evaluated. Consider:
user=> (macroexpand-1 '(->> a b c (x d e f)))
(x d e f (c (b a)))
If that makes sense, then just replace "x" with "->>":
user=> (macroexpand-1 '(->> a b c (->> d e f)))
(->> d e f (c (b a)))
user=> (macroexpand-1 '(->> d e f (c (b a))))
(c (b a) (f (e d)))
> The question I was asking is: does anyone rely on the current behavior?
> For people adapting this syntax for a query language, it's appealing to
> write:
>
> a->b()->c()
> ->union(d->e()->f())
>
> and get (union (c (b a) (f (e d)))
>
That's what:
(-> a b c (union (-> d e f)))
expands to.
- James
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