Create new function that supports 'quasi-quosure' syntax

Create new function that supports 'quasi-quosure' syntax

Usage

new_function2(
  args = alist(),
  body = {
 },
  env = parent.frame(),
  quote_type = c("unquoted", "quote", "quo"),
  quasi_env = parent.frame()
)

Arguments

args

named list of function formals

body

function body expression, supports 'quasi-quosure' syntax

env

declare environment of the function

quote_type

character, whether body is unquoted, quoted, or a 'quo' object (from 'rlang' package)

quasi_env

where the 'quasi-quosure' should be evaluated, default is parent environment

Value

a function

Details

An unquoted body expression will be quoted, all the expressions with 'quasi-quosure' like !!var will be evaluated and substituted with the value of var. For a 'quosure', quo_squash will be applied. A quoted expression will not be substitute, but will be expanded if any 'quasi-quosure' detected

args must be a list object, see formals. For arguments with no default values, or quoted defaults, use alist. An arg=alist(a=) will result in a function like function(a){...}. See examples for more details.

See also

new_function

Examples

# ------------ standard usage ------------
x <- 1:10
f1 <- new_function2(alist(a=), { print(a + x) }, env = environment())
f1(0)
#>  [1]  1  2  3  4  5  6  7  8  9 10

x <- 20:23
f1(0)  # result changed as x changed
#> [1] 20 21 22 23

# ------------ 'quasi-quosure' syntax ------------
x <- 1:10
f2 <- new_function2(alist(a=), { print(a + !!x) })
print(f2)
#> function (a) 
#> {
#>     print(a + 1:10)
#> }
#> <environment: 0x5591b8800668>

f2(0)
#>  [1]  1  2  3  4  5  6  7  8  9 10

x <- 20:23
f2(0)  # result doesn't change as f2 doesn't depend on x anymore
#>  [1]  1  2  3  4  5  6  7  8  9 10

# ------------ argument settings ------------

default <- 123

# default with values pre-specified
new_function2(list(a = default))   # function (a = 123){}
#> function (a = 123) 
#> {
#> }
#> <environment: 0x5591bb1300c0>

# default with values unevaluated
new_function2(list(a = quote(default)))   # function (a = default){}
#> function (a = default) 
#> {
#> }
#> <environment: 0x5591ba8ae078>
new_function2(alist(a = default))
#> function (a = default) 
#> {
#> }
#> <environment: 0x5591b8970670>

# missing default
new_function2(alist(a = ))    # function (a){}
#> function (a) 
#> {
#> }
#> <environment: 0x5591b8252378>