function as first class object

function as first class object

[Mehdi Saada]

I'm thinking only of a limited form.
Like writing:
type FILTER_TYPE is access function (S: in STRING) return STRING;
FILTER: FILTER_TYPE := ( TO_BASIC( TO_LOWER ) )'Access
Not sure of the syntax though. Could it done one way or another ? Since the language is taking a slightly functional approach.
I know my exemple can be done otherwise, but it means more lines to maintain, blablabla. Or maybe convoluted use of nesting functions into functions, are in fact so rare it's not worth it.

Re: function as first class object

[Dmitry A. Kazakov]

On 2018-01-15 17:20, Mehdi Saada wrote:
> I'm thinking only of a limited form.
> Like writing:
> type FILTER_TYPE is access function (S: in STRING) return STRING;
> FILTER: FILTER_TYPE := ( TO_BASIC( TO_LOWER ) )'Access
> Not sure of the syntax though. Could it done one way or another ?

Yes. You declare an abstract filter type with a primitive operation 
Apply. Then you create handles to that type with the same interface.

The purpose of the exercise is to escape limitness of the target types.

You derive an object from the abstract filter type with the function as 
the discriminant of. The implementation of Apply calls to the 
discriminant function.

You derive an object from the abstract filter type with a container of 
handles. The implementation of Apply calls Apply for the elements of the 
list passing the result as an argument to the next.

You define a compose operation, e.g. "+" on handles that creates an 
object with two handles in the list taken from the arguments and returns 
a handle to it.

That is.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de

Re: function as first class object

[Mehdi Saada]

That's what I had in mind... But it's quite verbose.

Re: function as first class object

[Dmitry A. Kazakov]

On 2018-01-15 18:46, Mehdi Saada wrote:
> That's what I had in mind... But it's quite verbose.

Not for the end user. For him it could be:

    +To_Basic'Access * +To_Lower'Access

or even reduced to:

    To_Basic'Access * To_Lower'Access

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de