These functions evaluate expr within a given environment (env for with_env(), or the child of the current environment for locally). They rely on eval_bare() which features a lighter evaluation mechanism than base R base::eval(), and which also has some subtle implications when evaluting stack sensitive functions (see help for eval_bare()).

with_env(env, expr)

locally(expr)

Arguments

env

An environment within which to evaluate expr. Can be an object with an get_env() method.

expr

An expression to evaluate.

Details

locally() is equivalent to the base function base::local() but it produces a much cleaner evaluation stack, and has stack-consistent semantics. It is thus more suited for experimenting with the R language.

Examples

# with_env() is handy to create formulas with a given environment: env <- child_env("rlang") f <- with_env(env, ~new_formula()) identical(f_env(f), env)
#> [1] TRUE
# Or functions with a given enclosure: fn <- with_env(env, function() NULL) identical(get_env(fn), env)
#> [1] TRUE
# Unlike eval() it doesn't create duplicates on the evaluation # stack. You can thus use it e.g. to create non-local returns: fn <- function() { g(get_env()) "normal return" } g <- function(env) { with_env(env, return("early return")) } fn()
#> [1] "early return"
# Since env is passed to as_env(), it can be any object with an # as_env() method. For strings, the pkg_env() is returned: with_env("base", ~mtcars)
#> ~mtcars #> <environment: base>
# This can be handy to put dictionaries in scope: with_env(mtcars, cyl)
#> [1] 6 6 4 6 8 6 8 4 4 6 6 8 8 8 8 8 8 4 4 4 4 8 8 8 8 4 4 4 8 6 8 4