Generators compatible with SRFI 121.
(make-iota-generator . args)
(make-range-generator . args)
(make-coroutine-generator proc)
(vector->generator . args)
(reverse-vector->generator . args)
(string->generator . args)
(bytevector->generator . args)
(make-for-each-generator for-each obj)
(make-unfold-generator stop? mapper successor seed)
(gcombine proc seed . gens)
(gdelete-neighbor-dups . args)
(gindex value-gen index-gen)
(gselect value-gen truth-gen)
(generator->reverse-list . args)
(generator->vector . args)
(generator->vector! vector at gen)
(generator->string . args)
(generator-fold f seed . #<undef>)
(generator-unfold g unfold . args)