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Re: Bugs (perhaps?) in behaviour of )COPY, )PCOPY with named lambda fns

From: Dr . Jürgen Sauermann
Subject: Re: Bugs (perhaps?) in behaviour of )COPY, )PCOPY with named lambda fns
Date: Sat, 10 Jul 2021 16:05:41 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0


I believe this is simply a misunderstanding of functionality.

Consider this (something similar happens if you )COPY the same script twice):

*      )CLEAR**
**      FOO←{ 42 ⊣ ⍵ }   ⍝ OK: create monadic defined function FOO (which returns 42)** **      FOO←{ 42 ⊣ ⍵ }   ⍝ ERROR: FOO is now a defined function, so you cannot assign anything to it.**
**      FOO←λ1**
**      ^   ^*

As matter of protection, in GNU APL you cannot re-define a named lambda without erasing it.
You can (and in most cases should), however, localize it.

As to )ERASE vs. ⎕EX: use )ERASE in immediate execution mode (preferably after )SIC) and ⎕EX in defined functions. In immediate execution (which includes scripts) it is a matter of preference which one you use and in which fashion you want to get the success of the of
the operation (error text for failed )ERASE or a boolean vector for ⎕EX).

Best Regards,

On 7/10/21 6:41 AM, Russtopia wrote:
I have noticed what I believe are some inconsistencies (bugs?) with how GNU APL handles reloading/overwriting/erasing of symbols which are 'trad fns' versus 'lambda fns'.

Consider the following )DUMP file:

#!/usr/local/bin/apl --script
⍝        ⍝
⍝ sink.apl                             2021-07-09  20:04:14 (GMT-8)  ⍝
⍝        ⍝

Life←{↑1 ⍵∨.∧3 4=+/,¯1 0 1∘.⊖¯1 0 1∘.⌽⊂⍵}

∇a←MatToVecArray M
 ⍝⍝ Return rows in M as an array of vectors
 ⍝⍝ lambda (dfn) version: {(⊂⍺){⍺[⍵;]}¨⍳≢⍵} ⍝⍨M

The above will )LOAD and )LOAD a second time, without error (as I presume it totally overwrites the current WS). However, )COPY or )PCOPY will give an error for the 'Life' function if it is already loaded into the current WS:

      )copy sink Life
DUMPED 2021-07-09  20:04:14 (GMT-8)
      )copy sink Life
DUMPED 2021-07-09  20:04:14 (GMT-8)
      ^    ^

Regular 'trad fns' can be re-loaded into the current WS without issue.

If I add in

⎕EX 'Life'

to sink.apl above the definition, )COPY and PCOPY will now succeed; but if I )DUMP this WS back to file, the ⎕EX is not part of the )DUMP output so problems will re-occur.

As an final note, as an APL newcomer: When is it preferable to use ⎕EX instead of )ERASE ?)


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