Jürgen,
Not to issue AXIS ERROR's on primitive functions where IBM APL2
does seems to be a fairly large deviation from Gnu-APL's claim to be
IBM APL2 compliant. Yes, having the ability to use axis specifications
with defined functions is a desirable extension to the language as long
as the feature does not interfere with the base language. Breaking
syntax checking looks like interference. With defined functions, the
person using the function is probably the person who wrote it, so
he/she knows the feature is there. With primitive functions the
documentation is sketchy and the user depends on the interpreter to
point out syntax errors. Trying to use a axis specification with a
primitive that does support it is a syntax error (at least, the IBM
APL2 documentation says it is).
Section 3.13 'Axis arguments in defined functions' of the
apl.html documentation does not give a hint of the non-existence of
syntax checking for primitive functions with respect to axis
specification support. Maybe a warning to that effect and a list of
Gnu-APL primitives supporting axis specifications can be added to the
section.
Regards,
Fred
> Hi Fred,
>
>
>
> this is actually a language extension which has a deeper
> background.
>
>
>
> I define a language extension to be a (different) behaviour of
> the
> interpreter when
>
> the standard or the IBM language reference return an error.
> Sometimes extensions
>
> are introduced or adopted from other interpreters (for example ⍳1
> 2
> 3 taken from
>
> Dyalog) or because the language becomes more general.
>
>
>
> So what you see is a language extension and the reason is this.
>
>
>
> 1. GNU APL supports axis arguments for defined functions. This is
> so
> that you can
>
> write proper wrapper functions around APL primitives. Since
> defined
> functions can
>
> not be overloaded you need a way to write a wrapper that can
> emulate
> the optional
>
> axis argument of the wrapped apl primitive. I was always annoyed
> by
> not being able
>
> to write such wrappers, in particular for benchmarking purposes.
>
>
>
> 2. Since the axis argument is optional in all apl primitives that
> can have one, the axis
>
> is also optional in GNU APL defined functions. You can check for
> its
> presence with
>
> ⎕NC just like for optional left arguments.
>
>
>
> 3. Another concept in GNU APL is that there shall be as few
> differences as possible
>
> between primitive functions (including ⎕-functions) and defined
> functions. A consequence
>
> of that (which simplifies the parser a lot) is that also all
> primitive function can have
>
> an axis argument. The default behaviour in both cases is to
> ignore
> the axis argument.
>
> That is what you see for ↑[] but also for all other primitives
> that
> have no axis variant.
>
> You can change that by changing e.g.
>
>
>
> virtual Token eval_AXB(Value_P A, Value_P X, Value_P B)
>
> { return eval_AB(A, B); }
>
>
>
> to:
>
>
>
> virtual Token eval_AXB(Value_P A, Value_P X, Value_P B)
>
>
> { SYNTAX_ERROR; }
>
>
>
>
>
> in all eval_XXX() functions declared in Function.hh
> that have an X (for axis) in their name. Since all functions
> are derived from this class it will change all primitives, but
>
> also all defined functions and operators. I personally would not
> do
> it, though.
>
>
>
> This language extension has been in GNU APL since almost day one.
> Therefore I
>
> cannot predict how often it is used (you can also do some dirty
> tricks with it). For
>
> that reason I believe it is better not to change it.
>
>
>
> Best Regards,
>
> Jürgen Sauermann
>
>
>
>
>
>
>
> On 07/04/2017 07:42 PM, Frederick Pitts
> wrote:
>
>
>
> > Hello Jürgen,
> >
> > The IBM 'APL2 Programming: Language Reference' suggests that
> > axis specification is not allowed with the first function in that
> > 'Figure 7. Functions and Operators That Allow Axis Specification',
> > page
> > 45, does not list 'First' by the '↑' symbol, whereas ravel,
> > catenate
> > and laminate are listed by the ',' symbol. The text under Figure 7
> > says
> > an AXIS ERROR occurs if a function or operator is not in the list.
> >
> > ISO/IEC 13751:2000(E)' contains 'Table 4: The Form Table',
> > pages 71-74, which claims to list all syntactic-units for which
> > evaluation sequences exist. The first function with axis
> > specification
> > does not appear in that table.
> >
> > Yet Gnu-APL allows
> >
> > ↑[ 2 ] 3 3 3 ⍳ 27
> > 1
> >
> > which is the first scalar in the ravel of the argument and the axis
> > specification is being ignored.
> >
> > Neither IBM or ISO specifications say that the first function
> > with axis specification is part of the language. I respectfully
> > submit
> > that Gnu-APL should report an attempt to use first function with
> > axis
> > specification as a syntax error.
> >
> > Regards,
> >
> > Fred
> >
> >
> >
> >
>
>
>
>
>
