121 (Generators) has been withdrawn in favor of 158 (Generators and Accumulators). IMHO 158 is definitely worth having. If 158 is a compatible superset of 121, I guess it doesn't hurt to have both. However, if there isn't much existing Scheme code depending on 121 it may be best to encourage everyone to switch to 158.
No particular support for these SRFIs is needed in order to return a generator or an accumulator from some code - those are just ordinary closures conforming to very simple conventions. These SRFIs contain ready-made higher-order functions to work with them.
121 (Generators) has been withdrawn in favor of 158 (Generators and Accumulators). IMHO 158 is definitely worth having. If 158 is a compatible superset of 121, I guess it doesn't hurt to have both. However, if there isn't much existing Scheme code depending on 121 it may be best to encourage everyone to switch to 158.
No particular support for these SRFIs is needed in order to return a generator or an accumulator from some code - those are just ordinary closures conforming to very simple conventions. These SRFIs contain ready-made higher-order functions to work with them.