Lab error?

[Michael Day]

I was having a retrospective  look at Help/Studio/Labs/GraphUtilities 
and encountered an error.  Here are some snippets from the session.
Section 5 worked ok.  

<<

Lab: Graph Utilities

To advance the lab, select menu Help|Studio|Advance or the

corresponding shortcut. 

── (1 of 24) Introduction ───────────────────────────────────

This lab describes the graph utilities (Graph) included with

J.

...

── (5 of 24) Drawing with gl2 commands (ctd) ────────────────

)

load 'c:/users/mike_/j9.7-user/temp/gl2demo.ijs'

── (6 of 24) Drawing with graph utilities ───────────────────

The next section draws the same square using Graph.

)

|control error in runquiet, defining explicit entity

|the line, with its number in its definition shown in brackets, has a mismatched control structure

| 3 :0''

|[-5]

Press ENTER to inspect

>>

I found this version of "runquiet", but don't know for sure whether it's the right locale. 
It looks ok to me! 

runquiet_jlab805_

3 : 0

cocurrent 'base'

0!:100 y [ 4!:55<'y'

)

I'm running 

JVERSION

Engine: j9.7.0-beta12/j64avx2/windows

Build: commercial/2026-02-14T02:11:10/clang-19-1-5/SLEEF=1

Library: 9.7.8

Qt IDE: 2.5.10/6.8.2(6.8.2)

OS Ver: Windows 11 Version 25H2 10.0.26200

Platform: Win 64

Installer: j9.7 install

InstallPath: c:/d/j9.7

Not too important for me,  unless my set-up is at fault, but somebody might need 

it to work.

Thanks,

Mike

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[Raul Miller]

Interestingly, this succeeds:
0!:100 yy [ 4!:55 <'yy' [ yy=: 'echo i.2 3'

this fails:
require'trace'
trace {{)n0!:100 yy [ 4!:55 <'yy' [ yy=: 'echo i.2 3'}}

but this succeeds:
trace {{)n(0!:100 yy) [ 4!:55 <'yy' [ yy=: 'echo i.2 3'}}

So ... I suspect an informal departure from J's formal grammar, which
has not been implemented consistently for all parsing contexts.

I hope this helps,

--
Raul

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[Henry Rich]

According to the rules, the value of yy should be stacked before the name is deleted. It is (no value error). The error is that the value is then deleted while it is on the execution stack. I'll look into a fix. 

Henry Rich

[Henry Rich]

I was away from my machine...

The problem is an error in the Lab.  In section 6 a verb is executed with

PREPARE
3 : 0''
if. 0=wdisparent <'gl2demo' do.
  load '~temp/gl2demo.ijs'
end.
PREPARE

but as you see, the ) at the end of the verb was omitted.  That is now
an error as of this release.  Adding in the ) fixes it.  I hope the
owner or another good citizen sees this & makes the change.

The problem Raul mentioned is likely an error in trace.  The value of yy
should be stacked before 4!:55 is executed, but the display suggests
that the name was stacked.  That fails because the name is expunged
before the value has been retrieved.

Henry Rich

[chris burke]

I have fixed the Graph Utilities lab.