(CBN) (Normal order reduction, leftmost, outermost reduction). An argument passing convention (first provided by ALGOL 60 ?) where argument expressions are passed unevaluated. This is usually implemented by passing a pointer to some code which will return the value of the argument and an environment giving the values of its free variable s. This evaluation strategy is guaranteed to reach a normal form if one exists.
When used to implement functional programming languages, call-by-name is usually combined with graph reduction to avoid repeated evaluation of the same expression. This is then known as call-by-need . The opposite of call-by-name is call-by-value where arguments are evaluated before they are passed to a function. This is more efficient but is less likely to terminate in the presence of infinite data structures and recursive functions. Arguments to macro s are usually passed using call-by-name.
(1994-11-29)