Well, + used to be the identify function before the introduction of complex
numbers. Now + is the conjugate function (conjugate is equal to identity
for reals).
I believe the identity function is useful when you have an operator where
you want the passed-in function to do nothing. A somewhat contrived example
would be an operator (let's call it ApplyPrint) that prints each element
after applying it to the operator. You'd call it like so:
{1+⍵}ApplyPrint 10 20 30
11
21
31
If you don't want to apply the function, just call the identify function:
⊢ApplyPrint 10 20 30 'foo'
10
20
30
foo
Silly example perhaps, but illustrates its usefulness.
Regards,
Elias
On 1 July 2014 23:04, Juergen Sauermann <[email protected]>
wrote:
> Hi Elias,
>
> I looked in "Mastering APL" from Dyalog and could not find it.
> They call + the identity function.
>
> And what would be the use of it?
>
> /// Jürgen
>
>
>
> On 06/30/2014 06:24 AM, Elias Mårtenson wrote:
>
>> I was looking at the Dyalog reference manual and realised that they
>> support monadic ⊢ (right) as the identity function. Adding support for this
>> in GNU APL is trivial.
>>
>> The attached patch implements this.
>>
>> Regards,
>> Elias
>>
>>
>
