call-by-need definition reduction
A reduction strategy
which delays evaluation of function arguments
until their values are needed. A value is needed if it is an argument to a primitive
function or it is the condition in a conditional
. Call-by-need is one aspect of lazy evaluation
The term first appears in Chris Wadsworth's thesis "Semantics and Pragmatics of the Lambda calculus" (Oxford, 1971, p. 183). It was used later, by J. Vuillemin in his thesis (Stanford, 1973).