UseFunction: Primary dispatcher for functional programming

Description

UseFunction is an alternative approach to function dispatching vis-a-vis UseMethod. It is designed for people interested in writing functional programs in R as opposed to object-oriented programs.

Usage

UseFunction(fn.name, ...)

Arguments

fn.name

The name of a function that uses functional dispatching. This is just the name of the function being defined

...

The arguments that are passed to dispatched functions

Value

Returns the value of the dispatched function

Details

Defining functions for dispatching based on guards requires following a simple template: fn.var <- function(...) UseFunction('fn.var', ...) Once this initial declaration is made, then guards and child functions can be declared. If the parent declaration is not made, then calling 'guard' will result in an error.

When calling the function, if no guards match, then an error is returned.

Examples

Run this code

# Note that these are trivial examples for pedagogical purposes. Due to their
# trivial nature, most of these examples can be implemented more concisely
# using built-in R features.
reciprocal <- function(...) UseFunction('reciprocal', ...)

guard(reciprocal.1, is.numeric(x) && x != 0)
reciprocal.1 <- function(x) 1 / x

guard(reciprocal.2, is.character(x))
reciprocal.2 <- function(x) reciprocal(as.numeric(x))

guard(reciprocal.default, TRUE)
reciprocal.default <- function(x) stop("Undefined for 0")

reciprocal(4)