Scheme Programming Language :: call by need + call by reference


	call by need + call by reference In EoPL the evaluator that implements call-by-need is built on the evaluator that implements call-by-reference. Is call-by-reference necessary? x is bound to a reference to a thunk and y is bound to the same reference. Why is it important for x and y to be bound to the same refererence? ((lambda(x) ((lambda (y) <expression>) x)) <expression>) Now that I've got the question out of my head and into words, I think I can see the reason - with call-by-reference the thunk is evaluated once somewhere and all procedures that have been passed the thunk will see (refer to) the expressed value.