[Rd] Using substitute to access the expression related to a promise

Hadley Wickham hadley at rice.edu
Mon May 2 15:53:45 CEST 2011

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
[1] 3

Is this a bug in substitute?

> sessionInfo()
R version 2.13.0 (2011-04-13)
Platform: x86_64-apple-darwin9.8.0/x86_64 (64-bit)


Assistant Professor / Dobelman Family Junior Chair
Department of Statistics / Rice University

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