[Rd] as.missing

[Peter Dalgaard]

Paul Gilbert <pgilbert at bank-banque-canada.ca> writes:

> >I.e., when x is missing in g, and g calls f(3,x), f will use its
> >default value for x.
> >  
> >
> Yes, that is the behaviour I am looking for. That is, f  should do what 
> it normal would do if it were called with x missing.

But if x has a default in g then that default should presumably be
used? And what if x is given a value in the evaluation frame of g
before it is used by f (which can happen, you know, even after the
evaluation of f has begun)? Now imagine a longer chain of calls.

I think what you're asking for is essentially dynamic scoping for
missing arguments: you'd have to backtrack along the call chain to
find the first instance where x is either given a value or has a
default. This sounds messy.

-- 
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