Process unquote operators in a captured expression
While all capturing functions in the tidy evaluation framework
perform unquote on capture (most notably quo()),
expr_interp() manually processes unquoting operators in
expressions that are already captured. expr_interp() should be
called in all user-facing functions expecting a formula as argument
to provide the same quasiquotation functionality as NSE functions.
expr_interp(x, env = NULL)
x |
A function, raw expression, or formula to interpolate. |
env |
The environment in which unquoted expressions should be evaluated. By default, the formula or closure environment if a formula or a function, or the current environment otherwise. |
# All tidy NSE functions like quo() unquote on capture:
quo(list(!!(1 + 2)))
# expr_interp() is meant to provide the same functionality when you
# have a formula or expression that might contain unquoting
# operators:
f <- ~list(!!(1 + 2))
expr_interp(f)
# Note that only the outer formula is unquoted (which is a reason
# to use expr_interp() as early as possible in all user-facing
# functions):
f <- ~list(~!!(1 + 2), !!(1 + 2))
expr_interp(f)
# Another purpose for expr_interp() is to interpolate a closure's
# body. This is useful to inline a function within another. The
# important limitation is that all formal arguments of the inlined
# function should be defined in the receiving function:
other_fn <- function(x) toupper(x)
fn <- expr_interp(function(x) {
x <- paste0(x, "_suffix")
!!! body(other_fn)
})
fn
fn("foo")Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.