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Re: Fwd: Definition of "first-thingy"

From: Dr . Jürgen Sauermann
Subject: Re: Fwd: Definition of "first-thingy"
Date: Thu, 20 Feb 2020 17:39:07 +0100
User-agent: Mozilla/5.0 (X11; Linux i686; rv:60.0) Gecko/20100101 Thunderbird/60.6.1

Hi Elias,

I believe "zero-dimensional array" is a synonym for "scalar" (or: an array
with: 0=⍴⍴Z.

It is not an empty array. Also in IBM APL2 enclosing a scalar, like in ⊂9,
is that same scalar and not a nested value.

Best Rewgards,

On 2/20/20 4:11 PM, Elias Mårtenson wrote:

---------- Forwarded message ---------
From: Elias Mårtenson <address@hidden>
Date: Thu, 20 Feb 2020, 22:39
Subject: Definition of "first-thingy"
To: <address@hidden>

One benefit of experimenting with low-level PAL behaviours is that I've spent much more time lately reading the ISO spec.

I was reading the specification for ↑ (first), which says that it returns "first-thingy" of the argument.

Now, the definitions section defines "first-thingy" as such:

First-thingy in A : An opration that for A , an array, returns an array B , defined as follows:
If A is empty, set B1 to the typical-element of A .
Otherwise, set B1 to the first-item of the ravel-list of A .
If B1 is a number or a character, set B to an array, whose ravel-list contains the single
item B1 , and whose shape-list is empty.
Otherwise, set B to B1 .

My impression from reading this is that this is not consistent with GNU APL's behaviour in the following case: ↑9

GNU APL returns the number 9 in this case, while it would seem it's supposed to return a 9 wrapped in a zero-dimensional array: ⊂9

Now, GNU APL evaluates ⊂9 to the number 9 as well, which I also feel isn't consistent.

Am I misreading the spec, or is there an inconsistency here?


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