wrapr includes de-referencing, function evaluation, and a new concept called "wrapr_applicable". "wrapr_applicable" is dispatch by type of right hand side argument scheme.
wraprThe wrapr pipe operators (%.>% and %>.%) are roughly defined as: a %>.% b ~ { . <- a; b };. This works under the assumption that b is an expression with free-instances of “.”. A typical use is:
library("wrapr")
5 %.>% sin(.)
#> [1] -0.9589243The above is performed by standard S3 dispatch on the left argument of an exported generic functions called apply_left() and apply_right(). A formal description of wrapr piping can be found here.
wrapr works primarily over expressions and “.”. wrapr does tries to de-reference names found in the right-hand side of pipe stages, and also dispatches functions. One can also write the following.
5 %.>% sin
#> [1] -0.9589243
5 %.>% base::sin
#> [1] -0.9589243"wrapr_applicable"Arbitrary objects ask wrapr to treat them as special expressions by overriding one or more of apply_left() and apply_right() for the S3 class they wish managed.
For example:
function_reference <- list(f = sin)
class(function_reference) <- c("wrapr_applicable", "ourclass")
apply_right.ourclass <- function(pipe_left_arg,
pipe_right_arg,
pipe_environment,
left_arg_name,
pipe_string,
right_arg_name) {
pipe_right_arg$f(pipe_left_arg)
}
function_reference
#> $f
#> function (x) .Primitive("sin")
#>
#> attr(,"class")
#> [1] "wrapr_applicable" "ourclass"
5 %.>% function_reference
#> [1] -0.9589243
function_reference$f <- sqrt
5 %.>% function_reference
#> [1] 2.236068The signature arguments work as follows:
pipe_left_arg: The value moving down the pipeline.pipe_right_arg: The right pipeline operator (essentially “self” or “this” in object oriented terms, used for S3 dispatch).pipe_environment: The environment the pipeline is working in (not usually needed).left_arg_name: If the left arguement was passed in by name, what that name was.pipe_string: The name of the pipe operator (not usually needed).right_arg_name: If the right arguement was passed in by name, what that name was.This functionality allows arbitrary objects to directly specify their intended pipeline behavior.
Let’s use a debugging function to see the values of all of the arguments.
apply_right.ourclass <- function(pipe_left_arg,
pipe_right_arg,
pipe_environment,
left_arg_name,
pipe_string,
right_arg_name) {
print("pipe_left_arg")
print(pipe_left_arg)
print("pipe_right_arg")
print(pipe_right_arg)
print("pipe_environment")
print(pipe_environment)
print("left_arg_name")
print(left_arg_name)
print("pipe_string")
print(pipe_string)
print("right_arg_name")
print(right_arg_name)
pipe_right_arg$f(pipe_left_arg)
}
5 %.>% function_reference
#> [1] "pipe_left_arg"
#> [1] 5
#> [1] "pipe_right_arg"
#> $f
#> function (x) .Primitive("sqrt")
#>
#> attr(,"class")
#> [1] "wrapr_applicable" "ourclass"
#> [1] "pipe_environment"
#> <environment: R_GlobalEnv>
#> [1] "left_arg_name"
#> NULL
#> [1] "pipe_string"
#> [1] "%.>%"
#> [1] "right_arg_name"
#> function_reference
#> [1] 2.236068
a <- 5
a %.>% function_reference
#> [1] "pipe_left_arg"
#> [1] 5
#> [1] "pipe_right_arg"
#> $f
#> function (x) .Primitive("sqrt")
#>
#> attr(,"class")
#> [1] "wrapr_applicable" "ourclass"
#> [1] "pipe_environment"
#> <environment: R_GlobalEnv>
#> [1] "left_arg_name"
#> a
#> [1] "pipe_string"
#> [1] "%.>%"
#> [1] "right_arg_name"
#> function_reference
#> [1] 2.236068wrapr values (left-hand sides of pipe expressions) are completely general. wrapr operators (right-hand sides of pipe expressions) are primarily intended to be expressions that have “.” as a free-reference. wrapr can also be used with right-hand sides that are function references or with arbitrary annotated objects.