Re: Recursion, Yo

On 14/04/2024 11:17, Ben Bacarisse wrote:

Lawrence D'Oliveiro <ldo@nz.invalid> writes:
 

On Sat, 13 Apr 2024 19:37:37 +0200, Janis Papanagnou wrote:

...

But maybe you can explain where or how there's something "thrown away".

>
This is a valid Algol 68 program (just tested with a68g):
>
     BEGIN PROC f = REAL : 3.1415; f END
>
It calls f, which returns a real, which is then cast to VOID -- i.e.
thrown away.

 You are just arguing about how you want to use an informal term: namely
to "throw away".  In Algol 68, the mode (AKA type) "void" is,
conceptually, a collection of values like any other.  The coercion
called voiding converts a value of some other type to the single value
of type void.  You could describe this a "throwing away the value", or
you could agree with Janis and say that the serial-clause you wrote
yields the sole value of type void.

It looks to me as though it yields a type REAL, as would this:
    BEGIN 1.23 END
If the context has no need for such a type, then it is discarded (although my own language would report an error for constructs like this that make no sense by themselves; most likely it is an actual mistake).
But in one like this:
    REAL x := BEGIN 1.23 END
Then that REAL value would be utilised.
Maybe you mean that in the first case, that REAL value is coerced to VOID, and that process is what causes it to be discarded. To me that sounds unwieldy.