Unexpected argument-matching when some are missing

Yes, I think all of that is correct. But y _is_ missing in this sense:

plot(1:10, y=)
...

Browse[2]> missing(y)

Although I said what I meant by 'missing' vs 'not present', it wasn't exactly what missing() means. My bad.
missing() returns TRUE if an argument is not specified in the call _whether or not_ it has a default, hence the behaviour of missing(y) in debug(plot).

But we can easily find out whether a default has been assigned:
plot(1:10, y=, type=)
Browse[2]> y
NULL
Browse[2]> type
"p"

... which is consistent with silent omission of 'y=' and 'type=' 


Still waiting for a guru...

Steve E



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