On 02/05/2011 9:53 AM, Hadley Wickham wrote:
Hi all,The help for delayedAssign suggests that you can use substitute to access the expression associated with a promise, and the help for substitute says: "If it is a promise object, i.e., a formal argument to a function or explicitly created using ‘delayedAssign()’, the expression slot of the promise replaces the symbol. But this doesn't seem to work: > a<- 1 > b<- 2 > delayedAssign("x", {message("assigning..."); a + b}) > substitute(x) x > x [1] 3 Is this a bug in substitute?
I think it is a design flaw rather than a bug: the global environment is handled specially. If you put those lines into a function you'll see different behaviour. I think if you really carefully read the documentation you'll find it says this.
I suggested regularizing this several years ago, but there were worries that it would break some common usage.
Duncan Murdoch
> sessionInfo() R version 2.13.0 (2011-04-13) Platform: x86_64-apple-darwin9.8.0/x86_64 (64-bit) ... Hadley
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