Lev and Dex

[Bob Armstrong]

The issue of the result of monadic lex motivated me to get a copy of Dyalog's current documentation to check that it really doesn't have a nil datum .

Way back I had a note in ⍞ titled " The Minimal APL Statement : sink nil , do nothing with nothing " . If you have a nil datum , which also must be its own datatype , it's the result of a verb which has no result .

That Arthur Whitney understood it's value is a significant reason for me to move to K despite its syntactical shortcomings . Here are some relevant snips from his documentation :

Nil
Nil is the value of an unspecified item in a list formed with parentheses and semicolons.
For example, nil is the item at index position 2 of (1 2;"abc";;‘xyz).
Nil is an atom; its value is _n , or *() . Nils have special meaning in the right
argument of the primitive function Index and in the bracket form of function application
...
d[] is identical to d ._n , or equivalently d@!#d for lists and d@!d for dictionaries;

( monadic " * " is K's First , Dyalog's monadic " ⊃ " )

It's one of the first notions I implemented in my work on 4th.CoSy .