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