 Call-by-name

Call-by-name passes a procedure argument so that each use of the formal parameter refers to the actual expression in its calling environment. In ALGOL 60, the report explains this through replacement with renaming to avoid accidental capture of identifiers. An expression can consequently be evaluated more than once.^[ref]

Suppose the actual argument is a[i]. The procedure reads its name parameter, changes i, and reads the parameter again. With call-by-name, the second access can select a different array entry. With call-by-value, both accesses use the value obtained before entering the procedure. This is also different from saving the original entry's address. Call-by-name does not imply lazy evaluation with memoization: repeated evaluation can repeat both work and side effects.