Interpreter bug with ⎕SIGNAL: a spurious RANK ERROR.

[petermsiegel]

Here is some odd INTERPRETER behaviour!!! I'm generating a SIGNAL with an unusual, but legit, unicode character: ⃠ ⎕UCS 128683 (hex 1F6AB) (Note: I replaced Unicode 128683 with 8416 (which looks similar) in this post, because the former triggered an SQL error in the FORUM on SUBMIT). Dyalog APL on MacOS decides there's a rank error in the ⎕SIGNAL message string (left arg), even though said string checks out as a proper character vector.

Code: Select all

)clear
clear ws
      ERRch←⎕UCS 128683
      ERRch
 ⃠      ⍝ a non-combining DO NOT ENTER (error) Symbol; contrast  ⃠ 8416
      (ERRch,'Help me!')⎕SIGNAL 11     ⍝ Bad interpreter?
RANK ERROR: A signalled message must be a character vector or scalar
      (ERRch,'Help me!')⎕SIGNAL 11
                        ∧
      ('Help me!') ⎕SIGNAL 11      ⍝ Expected behaviour
Help me!
      ('Help me!')⎕SIGNAL 11
                  ∧
      m←ERRch,'Help me!'           ⍝ Same song, next verse
      m
 ⃠Help me!                         
      m ⎕SIGNAL 11                  ⍝ Same refrain
RANK ERROR: A signalled message must be a character vector or scalar
      m ⎕SIGNAL 11
        ∧
      (m~⎕UCS 128683) ⎕SIGNAL 11    ⍝ Remove the symbol. All is well.
Help me!
      (m~⎕UCS 128683)⎕SIGNAL 11

Lesson learned: Don't use cute characters in error messages.
Here are the system details:

Interpreter:
Version: 17.1.36845
Platform: Mac-64
Edition: Unicode/64
Date: Aug 15 2019 at 00:08:18
Version: 4.2.3437
Platform: MacIntel
Date: 2019-08-13 14:55:17 +0200
Git commit: 691f47856e05a36f70847313b23e061a0cf95392

[Veli-Matti]

Hi, seemingly the []DR of the left argument cannot be 32 bit character:

      ⎕DR ⎕UCS 65535
160
      ⎕DR ⎕UCS 65536
320
      ((⎕UCS 65535),'Help me!')⎕SIGNAL 11 
�Help me!
      ((⎕UCS 65535),'Help me!')⎕SIGNAL 11
                              ∧
      ((⎕UCS 65536),'Help me!')⎕SIGNAL 11
RANK ERROR: A signalled message must be a character vector or scalar
      ((⎕UCS 65536),'Help me!')⎕SIGNAL 11
                              ∧

-Veli-Matti

[petermsiegel]

Thanks. That's a very good summary of the problem. I had tried Chinese characters (like UCS 20004), but I forgot, those are 16-bit chars and work fine.

Even the other "DO NOT ENTER" ⎕UCS 8416 misbehaves on output depending on what's before or after it, sometimes appearing as blanks and other times as defined, but that may relate to (non-standard) behaviour of combining characters in Dyalog's terminal output routines.

[AndyS|Dyalog]

I have a two part answer:

1. "That's bonkers" was the response to the RANK ERROR - we'll replace that with a DOMAIN ERROR in the next version of Dyalog APL.
2. Indeed the interpreter does not support 32-bit characters in ⎕SIGNAL. I've raised an RFE to ask for this, but there's no guarantee that we'll ever implement this.

[petermsiegel]

Thanks for this. It would be great if the reference guide could point out the limitation. Documentation that matches the actual behaviour pays for itself many times over.