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Is there any operator for Iterables that allows you to map with some mutable state, then push that state to the next iteration? Sort of like a reduce but only to map not to flatten. I suppose I could `fold`  with a mutable list of `Pairs`.

maybe <https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/-grouping/|Grouping>'s fold?

is `scan` or `scanReduce` what you’re after?
<https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/scan.html>
<https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/scan-reduce.html>
e.g. <https://pl.kotl.in/yIdPaEjIc>

Ultimately I just refactored the irritating code to eliminate this problem