(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
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
Arguments to macro
s are usually passed using call-by-name.