unexpected behaviour with lazyeval::lazy(c)

[dirkschumacher]

A call to lazyeval::lazy(c) leads to the output below. I was expecting it would simply return c for the expr.

lazyeval::lazy(c)
<lazy>
  expr: .Primitive("c")
  env:  <environment: R_GlobalEnv>

[egnha]

@dirkschumacher That behavior of lazyeval::lazy is a surprise to me, too. (Though not necessarily internally inconsistent: other primitive functions yield the same result, if I'm not mistaken.) One way to get around it is to use the (non-magical) SE version, lazyeval::lazy_:

lazyeval::lazy_(quote(c), environment())  # ... or some other environment
#> <lazy>
#>   expr: c
#>   env:  <environment: R_GlobalEnv>

Is there a case where you would need lazyeval::lazy but couldn't use lazyeval::lazy_ (with some additional work using substitute, say, to setup the right expression)?

[lionel-]

Please note that all the promise-based lazy stuff has to go away because it doesn't work well with the bytecode compiler, which R is going to enable by default soon. Plus the R maintainers consider the promise accessors to be private API (though they technically are exported in the public API). So the next iteration of lazyeval (in the rlang package) will only capture the expression and environment from the parent call (i.e., it won't have the lazy scope). We are trying to find a solution to keep being able to capture the original environments of dotted arguments.

[egnha]

@lionel- Did not realize that—thanks for the heads-up. Does this mean that, long term, the lazyeval::lazy* family of functions will be deprecated in favor of the formula-based lazyeval::f_* family of functions? Or will rlang supplant even that?

[lionel-]

rlang will supplant it because f_capture() currently has the same semantics as lazy(): it has the same scope as lazy evaluation (and will thus climb arguments across calls). The rlang version will only capture the direct argument and the direct parent frame.

[lionel-]

for now I suggest to continue using lazy_dots() as we'll provide a drop-in replacement for it (probably less efficient), and replace lazy() in your code with f_new(substitute(arg), env = parent.frame()).