Result sequences

Expression evaluation in conventional programming languages may be viewed as a simplification of expression evaluation in the Icon programming language. The evaluation of an expression in Icon may yield a sequence of results. Goal-directed evaluation causes expressions to produce these results in an attempt to produce the successful evaluation of an enclosing expression. There are control operations that operate on result sequences. The study of expression evaluation in Icon therefore is more interesting than it is in most programming languages. This paper introduces a notation for result sequences and shows how it can be used to describe the static aspects of expression evaluation. Equivalences among control operations and expressions are demonstrated.