Re: [Bug-apl] Restrictions on localization of system variables?

[Kacper Gutowski]

On 2014-05-27 18:06:06, Juergen Sauermann wrote:
> Note that there are some subtle differences between IBM APL2 and GNU APL
> when localizing ⎕-vars. In IBM APL2 they are undefined after localizing
> them.
> In GNU APL they are pre-initialized with their respective default values.
> This
> gives simpler (and therefore faster code) because no check for validity is
> needed
> for the variables themselves, but also for the many internal users of them.

This indeed makes things simpler and I like the idea, but APL2's behavior
is mandated by ISO 13751 which at the beginning of chapter 12 says:

> Note: When a system-variable-symbol is localised the initial class of
> its associated system-parameter is nil.  If a primitive operation is
> invoked that requires a system parameter whose class is currently nil,
> the primitive operation signals implicit-error.  Therefore, a
> conforming-program that localises system-variable-symbols should
> assign them values from their internal-value-set before calling
> primitive operations that require them.


-k