call-by-name
call-by-name
(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.
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.