This brings up an interesting point. Truth is, the functional programming
model is extremely slow unless, as it often is, the function call is
optimized out.
On Mon, Mar 30, 2020 at 6:51 AM Elias Mårtenson <loke...@gmail.com> wrote:
> Thank you for the clarification. I can see that the problem isn't that the
> lambda function is slow. It's the +/ variant that is really fast. :-)
>
> Of course, as you say, in real code you'd never write it the way I did. :-)
>
> Regards,
> Elias
>
> On Mon, 30 Mar 2020 at 17:53, Dr. Jürgen Sauermann <
> mail@jürgen-sauermann.de> wrote:
>
>> Hi Elias,
>>
>> in GNU APL (and I suppose also in other APLs) lambda expressions are not
>> macros (or inline functions) but fully-fledged defined functions.
>> That is,
>>
>> *{⍺+⍵}/ ⍳1000000* is NOT equivalent to: *+/ ⍳1000000*
>>
>> Rather:
>>
>>
>>
>>
>> *∇Z←A PLUS B Z←A + B ∇ *
>> and then:
>>
>> *{⍺+⍵}/ ⍳1000000* is equivalent to: *FOO/⍳1000000*
>>
>> The 12 seconds are mainly spent for one million calls
>> of FOO, each call passing two scalar arguments A and B
>> and returning a scalar Z. It also wraps every Cell (i.e. every
>> ravel item) of A, B, and Z into a scalar value A, B, and Z.
>> Ravel cells are rather light-weight while values are more heavy
>> (each scalar value has, for example, its own shape vector).
>> And finally: each call of FOO pushes and pops an )SI entry and
>> a value stack entry for each A, B, and Z. These operations
>> are pretty fast but become noticeable if you do them very often.
>>
>> In your example one call of FOO takes 12 micro-seconds which
>> is, IMHO, not too bad.
>>
>> You could have avoided this overhead by computing:
>>
>> *{+/ ⍵} ⍳1000000* instead of: *{⍺+⍵}/ ⍳1000000*
>>
>> Best Regards,
>> Jürgen Sauermann
>>
>>
>> On 3/30/20 3:39 AM, Elias Mårtenson wrote:
>>
>> The following expression takes about 12 seconds to compute on my laptop:
>>
>> *{⍺+⍵}/ ⍳1000000*
>>
>> However, the equivalent expression without the lambda expression is
>> immediate (i.e. thr prompt returns before I have time to notice that it
>> even started calculating):
>>
>> *+/ ⍳1000000*
>>
>> What is causing the large difference in performance?
>>
>> Regards,
>> Elias
>>
>>
>>
