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. |

#> <quosure: local> #> ~list(3)# 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)#> <quosure: local> #> ~list(3)# 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)#> <quosure: local> #> ~list(~3, 3)# 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#> function (x) #> { #> x <- paste0(x, "_suffix") #> toupper(x) #> } #> <environment: 0x7f979f294030>fn("foo")#> [1] "FOO_SUFFIX"