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[fallow oar]

do you know about union types?

https://www.typescriptlang.org/docs/handbook/2/everyday-types.html#union-types

if you can describe both interfaces, you can "or" them together with |

type Foo = Bar[] | WhateverYourGeneratorThingyLooksLike

oops, i meant so send another message here but somehow that didn't happen

but you might want to take a look at Iterable as well. the thing that a generator function returns is an Iterable, and so are arrays. that common subset might be what you want (depending on what your 2nd implementation actually looks like)

more deets: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols