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- Subject: Re: Signature of iterator factories
- From: Mark Hamburg <mark@...>
- Date: Tue, 3 Nov 2009 08:04:25 -0800
On Nov 3, 2009, at 3:33 AM, Roberto Ierusalimschy wrote:
I am sorry, but I sent a wrong reply. I thought his proposal was to
have an extra hidden (but unique) control variable before the visible
variables in the loop. That is, the statement
for a,b,c in exp do
would be really
for _,a,b,c in exp do
with '_' hidden from the programmer.
That could be useful in cases where one might want to have an iterator
return nil for the first visible state variable. For example, imagine
wanting an iterator that would deliver just the values from an array
over a range -- values( array, lo, hi ) -- this won't work if there is
a nil in the array.
I had better examples where I'd wished for this, but the caffeine
hasn't kicked in enough this morning for me to remember them.