On 2020-08-03 11:52, Brian Schott wrote:
This thread hints at a problem I am having.
In particular the link suggested by Henry
https://code.jsoftware.com/wiki/Vocabulary/ErrorMessages#value
My problem is that I want to detect an error caused by an undefined
noun
but my attempt does not produce the desired error using :: .
For example in the example below, although `a` is undefined, I do not
get
the desired result, 0, from my verb `tally` when I execute `tally a`.
How can I define tally to produce 0 for an undefined argument. Or how
do I
detect an undefined argument, in general? I have considered using a
try.
... catch. in an explicit definition, but to me that seems unnecessary.
a
|value error: a
tally =: # :: 0:
tally i. 4
4
tally a
tally a
Is it important to catch it interactively like this?
If you're being given variable names from untrusted input that might
be wrong, then you can evoke the names (m~) instead of doing them (".n)
to get an error:
a =: i.5
'a'~
0 1 2 3 4
clear''
'a'~
|value error: a
On Wed, Nov 6, 2019 at 5:11 AM Henry Rich <henryhr...@gmail.com> wrote:
https://code.jsoftware.com/wiki/Vocabulary/ErrorMessages#value
Henry Rich
On 11/6/2019 4:26 AM, Arnab Chakraborty wrote:
> Dear all,
>
> Here is a behavior that I noticed only recently, and it puzzles me a
> lot:
>
> Let's say abc and xyz are not defined in my J session, and type just
abc
> by itself in a line. Of course, I get a value error. But if I type
>
> xyz abc
>
> then J does not produce any error, but simply echos back what I have
typed!
> I expected that J would start executing from the right, encounter abc,
and
> produce a value error. If I now define abc (say abc=. 0), then
>
> xyz abc
>
> produces a value error (expected) about xyz.
>
> But why does J become silent in presence of multiple undefined symbols?
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