Method Combinators

From LRDE

Abstract

In traditional object-oriented languages, the dynamic dispatch algorithm is hardwired: for every polymorphic callonly the most specific method is used. Clos, the Common Lisp Object System, goes beyond the traditional approach by providing an abstraction known as emphmethod combinations: when several methods are applicable, it is possible to select several of them, decide in which order they will be called, and how to combine their resultsessentially making the dynamic dispatch algorithm user-programmable.par Although a powerful abstractionmethod combinations are under-specified in the Common Lisp standard, and the Mop, the Meta-Object Protocol underlying many implementations of Clos, worsens the situation by either contradicting it or providing unclear protocols. As a consequence, too much freedom is granted to conforming implementations. The exact or intended behavior of method combinations is unclear and not necessarily coherent with the rest of Clos.par In this paper, we provide a detailed analysis of the problems posed by method combinations, the consequences of their lack of proper specification in one particular implementationand a Mop-based extension called emphmethod combinators, aiming at correcting these problems and possibly offer new functionality.

Documents

Bibtex (lrde.bib)

@InProceedings{	  verna.18.els,
  author	= {Didier Verna},
  title		= {Method Combinators},
  booktitle	= {11th European Lisp Symposium},
  isbn		= 9782955747421,
  year		= 2018,
  month		= apr,
  address	= {Marbella, Spain},
  abstract	= {In traditional object-oriented languages, the dynamic
		  dispatch algorithm is hardwired: for every polymorphic
		  call, only the most specific method is used. \textsc{Clos},
		  the Common Lisp Object System, goes beyond the traditional
		  approach by providing an abstraction known as \emph{method
		  combinations}: when several methods are applicable, it is
		  possible to select several of them, decide in which order
		  they will be called, and how to combine their results,
		  essentially making the dynamic dispatch algorithm
		  user-programmable.\par Although a powerful abstraction,
		  method combinations are under-specified in the Common Lisp
		  standard, and the \textsc{Mop}, the Meta-Object Protocol
		  underlying many implementations of \textsc{Clos}, worsens
		  the situation by either contradicting it or providing
		  unclear protocols. As a consequence, too much freedom is
		  granted to conforming implementations. The exact or
		  intended behavior of method combinations is unclear and not
		  necessarily coherent with the rest of \textsc{Clos}.\par In
		  this paper, we provide a detailed analysis of the problems
		  posed by method combinations, the consequences of their
		  lack of proper specification in one particular
		  implementation, and a \textsc{Mop}-based extension called
		  \emph{method combinators}, aiming at correcting these
		  problems and possibly offer new functionality.}
}