Proto is an R package that facilitates prototype programming, a
type of object-oriented programming that does not use classes as
an atomic concept (but is powerful enough to encompass them).

The package is lightweight providing a thin layer on top of R
environments. Unlike other packages which grow over time proto has
become smaller over time as it was successively polished to reduce
it to its essentials. Despite its small size prototype-based systems
can be more powerful than more complex class-based systems.

WWW: https://github.com/hadley/proto