nl_tokens: Yield all items in every iterable returned by the mapper when applied to every item in the source iterable
pl_tokens: function flatMap ( mapper ) { return function * ( iterable ) { let index = 0 ; for ( const <mask> of iterable ) { const innerIterable = mapper ( value , index ) ; for ( const inner of innerIterable ) { yield inner ; } index = index + 1 ; } } ; }