This is what I got from J806
   foo
3 : 0
if. _ - _ do.
 echo 1
else.
 echo 0
end.
EMPTY
)
   foo''
|NaN error: foo
|   _    -_
   bar
3 : 0
if. _. do.
 echo 1
else.
 echo 0
end.
EMPTY
)
   bar''
1

foo is reasonable.
bar is also reasonable to me, because _. is not equal 0 so that
the condition is true.

What is your code that treating _. as false?

Also on my J806 linux64
   2 7 p.1e308j_
_j_


Пт, 29 дек 2017, Louis de Forcrand написал(а):
> What about control structures treating _. as false?
> I personally would make that an error, and I would also say that code that 
> makes use of this should be considered bad style.
> 
> Louis
> 
> > On 29 Dec 2017, at 18:29, Henry Rich <[email protected]> wrote:
> > 
> > Surely not intended.  Put it on the bug list.
> > 
> > Henry Rich
> > 
> > On 12/29/2017 6:06 PM, Louis de Forcrand wrote:
> >> On the Indeterminate vocabulary page of the dictionary it is written
> >> 
> >> The only ways to create _. are as follows:
> >>            direct entry of _.
> >>            ".
> >>            3!:n
> >>            DLL call (database, LAPACK, etc.)
> >> 
> >> and
> >> 
> >> Primitives on arguments not containing _. signal NaN error instead of 
> >> producing _. .
> >> 
> >> yet (in j64-805 on macOS 10.10.5)
> >> 
> >>    2 7 p.1e308j_
> >> _.j_
> >> 
> >> This is very dangerous, as comparison with _. seems to yield _. and it 
> >> also seems that control structures treat _. as false instead of signalling 
> >> an error (which is in my opinion a very bad idea).
> >> Are both these behaviours intended?
> >> 
> >> Thanks,
> >> Louis
> >> 
> >> ----------------------------------------------------------------------
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> > 
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