Re: [R] Evaluation of defaults in functions

From: hadley wickham <h.wickham_at_gmail.com>
Date: Fri 29 Sep 2006 - 14:12:01 GMT

> > But doesn't R has a rather limited force of lazy evaluation? - you
> > have no control over it, apart from that arguments are evaluated
> > lazily. This rather limited compared to other languages (no lazy
> > lists etc)
>
> You do have more control than that. You can't put a promise in a list,
> but you can put one in an environment, e.g.
>
> > x <- new.env()
> > y <- 1
> > delayedAssign("z", y, assign=x)
> > y <- 2
> > x$z
> [1] 2

That's interesting. Is it possible to treat an environment like a list in most situations?

I had experimented with lazy lists/streams in R a while go (as they seem like a very natural way of dealing with datasets that are too large to fit in memory) but got stuck. This might let me get a little further.

Hadley



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