Re: [Rd] question about an R idiom: eval()ing a quoted block
In the case of power.t.test, there is a situation where you want to create 4
different functions with the same function body, in order to pass them to
uniroot(). I think that at the time, it just seemed convenient to express that
idea with a quote-eval (macro-like) construction, rather than figure out how to
do it with functions. I suppose that it could have been done neatly enough
along the lines of
g <- function(x1, x2, x3, x4)
{
f <- function(x1, x2, x3, x4) {...body...}
if (is.null(x1)
x1 <- uniroot(function(x1) {target - f(x1, x2, x3, x4)}, )$root
}
This adds an extra layer of function call, but probably makes the byte compiler
happier!
You might also use the ... argument to uniroot() as in
x1 <- uniroot(f, x2=x2, x3=x3, x4=x4, ..other args..)$root
but that gets a bit clunky.
-pd
> On 12 Jul 2023, at 00:01 , Ben Bolker wrote:
>
> In a few places in the R source code, such as the $initialize element of
> `family` objects, and in the body of power.t.test() (possibly other power.*
> functions), sets of instructions that will need to be run later are
> encapsulated by saving them as an expression and later applying eval(),
> rather than as a function. This seems weird to me; the only reason I can
> think of for doing it this way is to avoid having to pass back multiple
> objects and assign them in the calling environment (since R doesn't have a
> particularly nice form of Python's tuple-unpacking idiom).
>
> Am I missing something?
>
> cheers
> Ben
>
>
> https://github.com/r-devel/r-svn/blob/eac72e66a4d2c2aba50867bd80643b978febf5a3/src/library/stats/R/power.R#L38-L52
>
> https://github.com/r-devel/r-svn/blob/master/src/library/stats/R/family.R#L166-L171
>
> __
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> https://stat.ethz.ch/mailman/listinfo/r-devel
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Solbjerg Plads 3, 2000 Frederiksberg, Denmark
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Re: [Rd] question about an R idiom: eval()ing a quoted block
On 11/07/2023 6:01 p.m., Ben Bolker wrote: In a few places in the R source code, such as the $initialize element of `family` objects, and in the body of power.t.test() (possibly other power.* functions), sets of instructions that will need to be run later are encapsulated by saving them as an expression and later applying eval(), rather than as a function. This seems weird to me; the only reason I can think of for doing it this way is to avoid having to pass back multiple objects and assign them in the calling environment (since R doesn't have a particularly nice form of Python's tuple-unpacking idiom). Am I missing something? cheers Ben https://github.com/r-devel/r-svn/blob/eac72e66a4d2c2aba50867bd80643b978febf5a3/src/library/stats/R/power.R#L38-L52 https://github.com/r-devel/r-svn/blob/master/src/library/stats/R/family.R#L166-L171 Those examples are very old (the second is at least 20 years old). It may be they were written by someone who was thinking in S rather than in R. As far as I recall (but I might be wrong), S didn't have the same scoping rules for accessing and modifying local variables in a function from a nested function. Duncan Murdoch __ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
[Rd] question about an R idiom: eval()ing a quoted block
In a few places in the R source code, such as the $initialize element of `family` objects, and in the body of power.t.test() (possibly other power.* functions), sets of instructions that will need to be run later are encapsulated by saving them as an expression and later applying eval(), rather than as a function. This seems weird to me; the only reason I can think of for doing it this way is to avoid having to pass back multiple objects and assign them in the calling environment (since R doesn't have a particularly nice form of Python's tuple-unpacking idiom). Am I missing something? cheers Ben https://github.com/r-devel/r-svn/blob/eac72e66a4d2c2aba50867bd80643b978febf5a3/src/library/stats/R/power.R#L38-L52 https://github.com/r-devel/r-svn/blob/master/src/library/stats/R/family.R#L166-L171 __ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
