.BG
.FN missing
.TL
Check for missing arguments
.CS
missing(name)
.AG name
the name of one of the arguments to the function from which the call
to `missing' occurs.
.RT
`TRUE' if the current call did not supply the argument named, `FALSE'
if it did.
It is an error if the argument to `missing' is not a name or not the name
of an argument.
Note that `missing' allows arguments to be omitted even though no default
value is supplied (provided that some appropriate action is taken before
the value of the argument is needed).
.EX
if(!missing(weight))y <- y * sqrt(weight)
.KW programming
.WR
