[Jprogramming] Tacit definition using Amend

[Dan Bron]

Donn,

I think I intended that "it's difficult" for the implementor of J (Roger) to design an adverb such that it can be used tacitly, allowing for any of its 3 arguments to be calculated.  Not to deter you ;)

The foreign  5!:2  is not a one to one mapping (different inputs can produce identical outputs).  For example, the bane of newbies:

	   scalar    =.  1
	   vector    =. ,1
	   character =. '1'

	   ,  5!:2 ;: 'scalar vector character'
	+-+-+-+
	|1|1|1|
	+-+-+-+

To address this problem, the foreign  5!:0  is introduced.  Unlike  5!:2  , it does guaruntee unique outputs for unique inputs.  In your example, the clue lies in the differences of the atomic representations:

>	││ ││┌─┬────────────────┐│││
>	││ │││0│┌──┬─────────┬─┐││││

vs:

>	││ ││┌─┬────────────────┐│││
>	││ │││3│┌──┬─────────┬─┐││││

In atomic form, the left hand box in a pair tells you what class of what's contained in the right hand box (though be careful, because the implementation contains bugs).

Specifically,  5!:0  is telling you that there are certain sets of nouns (class  0  ) and verbs (class  3  ) that have identical displays.  In this case, it's a gerund (noun) versus a train (verb):

	   averb =. 1: 2: 3:
	   anoun =. 1:`2:`3:

	   averb 0
	2
	   anoun 0
	|syntax error
	|       anoun 0


	   5!:2 ;: 'averb anoun'
	+--+--+--+
	|1:|2:|3:|
	+--+--+--+
	|1:|2:|3:|
	+--+--+--+		   

-Dan