`crow/col/util.crow` (source)

`and-concat`[`col`] `record` `nominal`

inner col

AKA 'flat-map'

`for-loop`[`out-elem`, `in-col`, `in-elem`] `out-elem` `array`(`a` `in-col` `and-concat`, `f` `mut` `out-elem` `array`(`in-elem`)) (`in-col`, `in-elem`) `iterate`

`split`[`col`, `iter`, `elem`] `col` `array`(`a` `col`, `b` `col`) (`iter`, `col`) `begin-end`, (`elem`, `iter`) `next`, (`col`, `iter`) `slice`, `elem` `equal`

`groupable`[`col`, `iter`] `spec` (`iter`, `col`) `begin-end`, `iter` `subtract-to-nat`, `iter` `skip-next`, (`col`, `iter`) `slice`, `col` `size`

`groups-of`[`col`, `iter`] `col` `array`(`a` `col`, `group-size` `nat64`) (`col`, `iter`) `groupable`