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

In most situations (i.e. following the conventions outlined by the futile.paradigm), explicit use of UseFunction is unnecessary as the system will automatically generate and execute this command as necessary. The only time it is necessary is when an abstract function has an ambiguous name (typically containing extraneous dots).

Explicit function definitions follow a simple template: fn.var <- function(...) UseFunction('fn.var', ...)

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.

# Optional
#reciprocal <- function(...) UseFunction('reciprocal', ...)

reciprocal %when% is.numeric(x)
reciprocal %also% (x != 0)
reciprocal %must% (sign(result) == sign(x))
reciprocal %as% function(x) 1 / x

reciprocal %when% is.character(x)
reciprocal %as% function(x) reciprocal(as.numeric(x))

print(reciprocal)
reciprocal(4)