Like any self-respecting Lisp dialect, Emacs Lisp does come with a slew of predicates which regularly confuse newcomers to the language. As I’m hacking on a one-letter library for vector operations, I did research whether there were any lesser common ones I could reuse for even more succinct code. nlistp qualifies as it’s the negated variant of listp[1], the other one I’ve found was natnump which checks whether its argument is a natural number. Finally, I’ve found wholenump which I did assume to be a predicate for whole numbers, but apparently it’s not. In English you would call these “integers”, so integerp is what you’d want. What exactly would wholenump do then?
Using F1 v on both natnump and wholenump gave me docstrings showing exactly the same text save the function names. Using find-function on them leads me to the definition of natnump. What is going on here and why does the help system not list wholenump as alias to natnump despite it behaving like one?
data.c knows the culprit:
set_symbol_function (Qwholenump, XSYMBOL (Qnatnump)->function);
| [1] | The byte-compiler even turns nlistp into (not (listp ...)), so I suspect it’s an archaic variant given the low number of occurrences in the sources. |