Control delimiters and their hierarchies

Abstract

Since control operators for theunrestricted transfer of control are too powerful in many situations, we propose thecontrol delimiter as a means for restricting control manipulations and study its use in Lisp- and Scheme-like languages. In a Common Lisp-like setting, the concept of delimiting control provides a well-suited terminology for explaining different control constructs. For higher-order languages like Scheme, the control delimiter is the means for embedding Lisp control constructs faithfully and for realizing high-level control abstractions elegantly. A deeper analysis of the examples suggests a need for an entirecontrol hierarchy of such delimiters. We show how to implement such a hierarchy on top of the simple version of a control delimiter.