expr_interp

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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.

Usage
expr_interp(x, env = NULL)
Arguments
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.

Aliases
  • expr_interp
Examples
# NOT RUN {
# 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")
# }
Documentation reproduced from package rlang, version 0.1.6, License: GPL-3

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