<reduction> (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 a thunk - some code which will return the value of the
argument and an environment giving the values of its free
variables.
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 macros are usually passed using call-by-name.
(2006-05-27)
Nearby terms:
Calico « California State University San Marcos « callback « call-by-name » call-by-need » call-by-reference » call-by-value
