Since all recursive programs can be converted into iterative programs then you can "simply" (not always simple) convert recursive solutions like McCarthy's Lisp

Since all recursive programs can be converted into iterative programs then you can "simply" (not always simple) convert recursive solutions like McCarthy's Lisp solution to a loop: https://dl.acm.org/action/showFmPdf?doi=10.1145%2F1045283 https://dl.acm.org/action/showFmPdf?doi=10.1145%2F1045283 (page 5) (DE SAMEFRINGE (X Y) (OR (EQ X Y) (AND (NOT (ATOM X)) (NOT (ATOM Y)) (SAME (GOPHER X) (GOPHER Y))))) (DE SAME (X Y) (AND (EQ (CAR X) (CAR Y)) (SAMEFRINGE (CDR X) (CDR Y)))) (DE GOPHER (U) (COND ((ATOM (CAR U)) U) (T (GOPHER (CONS (CAAR U) (CONS (CDAR U) (CDR U))))))) Coroutines are not necessary for solving that problem (though they do offer a neat solution to it).