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.

Basic wrapr

The 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:

The 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.

Dereferencing and function evaluation

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.


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:

The 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.


wrapr 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.