quote(expr) will make no changes in expr, it just returns its one argument,
unevaluated.
substitute could be used in your lapply(..., library) example to give
library a name instead
of a character string for an input (which might be necessary if the
character.only argument
were not available)
l
Thanks again Bill; I agree that substitute is overkill here.
As an aside, for cases where someone may be tempted to use substitute(),
it seems quote() might be a safer alternative; compare
> lapply(list(1), function(y) c(quote(y), substitute(y)))
[[1]]
[[1]][[1]]
y
[[1]][[2]]
Functions, like your loader(), that use substitute to let users confound
things and their names, should give the user a way to avoid the use of
substitute. E.g., library() has the 'character.only' argument; if TRUE
then the package argument is treated as an ordinary argument and not passed
through
Thanks Bill. I think my confusion may have been in part due to my
conflating two distinct meanings of the term "evaluate"; the help for
force says it "forces the evaluation of a function argument" whereas the
help for eval says it "evaluates the ... argument ... and returns the
computed value".
1: substitute(), when given an argument to a function (which will be a
promise) gives you the unevaluated expression given as the argument:
> L <- list(a=1, b=2, c=3)
> str(lapply(L, function(x) substitute(x)))
List of 3
$ a: language X[[i]]
$ b: language X[[i]]
$ c: language X[[i]]
The 'X' a
Hi,
I thought I understood the change to lapply semantics resulting from this,
https://bugs.r-project.org/bugzilla/show_bug.cgi?id=16093
However, would someone care to explain why this does not work?
> L <- list(a=1, b=2, c=3)
> str(lapply(L, function(x){ y <- substitute(x); force(x);
