Julian and Henry (and Devon whose ideas extends Henry's, I think), Both of your solutions seem to require 'a' not just a. But still they might work for me.
My examples below are meant to show that I get to the 'Got here' line when a is defined and its # is not zero. I was hoping there was an easier way. First is based on Henry's ifdefined and it works for me. ifundefined_z_ =: 0 > [: 4!:0 < tallyH =: monad define if. ifundefined 'a' do. return. end. if. 0=#a do. return. end. 'Got here' ) erase<'a' 1 tallyH '' #a =. i. 0 0 tallyH '' #a =. i. 2 3 2 tallyH '' Got here Next is tally based on Julian's idea, but I could not make it work. My bad. tallyJ =: monad define try. 'a'~ catch. return. end. if. 0=#a do. return. end. 'Got here' ) erase<'a' 1 tallyJ'' |syntax error: tally | 0=#a 'a'~ |value error: a Finally, here is an alternative of mine which seems to work, too. tallyB =: monad define try. if. 0=#a do. return. end. catch. return. end. 'Got here' ) a |value error: a tallyB'' a =. i. 0 tallyB'' a =. i. 2 3 tallyB'' Got here On Mon, Aug 3, 2020 at 1:07 PM Julian Fondren <jfond...@minimaltype.com> wrote: > 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? > >> > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm > -- (B=) <-----my sig Brian Schott ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
