call-by-need

call-by-need

(reduction)A reduction strategy which delays evaluation offunction arguments until their values are needed. A valueis needed if it is an argument to a primitive function or itis the condition in a conditional. Call-by-need is oneaspect of lazy evaluation.

The term first appears in Chris Wadsworth's thesis "Semanticsand Pragmatics of the Lambda calculus" (Oxford, 1971, p. 183).It was used later, by J. Vuillemin in his thesis (Stanford,1973).