mikmart / monad

Monad Operators and Generics

monad

monad provides generic operators for monadic classes. Features include:

• fmap(), bind() and join() S7 generic functions.
• %>>% and %>-% pipe operators for fmap() and bind() respectively.

Implementations of the generics are provided for:

• The list built-in type.
• The maybe S3 class from the maybe package.

Implementing classes must provide fmap() and either bind() or join(), and the method implementations must satisfy the functor and monad laws.

Installation

Install from GitHub with:

# install.packages("pak")
pak::pak("mikmart/monad")

monad's Issues

Are there useful methods to be added for base classes?

list() comes to mind. Also possibly if you contort a bit you could see a NULL/default method as a kind of undeclared Maybe.

Should the generics use S3 instead of S7?

Some context here: armcn/maybe#10

I can't work out a simple way for an implementing package to register methods and to avoid a hard dependency on S7. With S3 the registrations would be trivial and only require Enhances: monad, e.g. with {maybe}:

#' @exportS3Method monad::fmap
fmap.maybe <- function(m, f, ...) {
  maybe_map(m, f, ...)
}

#' @exportS3Method monad::bind
bind.maybe <- function(m, f, ...) {
  and_then(m, f, ...)
}

#' @exportS3Method monad::join
join.maybe <- function(m) {
  maybe_flatten(m)
}