grouping function like split or chunked, but gives you access to the whole group so far in the predicate

Grouping.swift

extension Collection {
    func grouping(isMember: (SubSequence, Element) throws -> Bool) rethrows -> [SubSequence] {
        var result: [SubSequence] = []
        var start = self.startIndex
        
        for end in self.indices.dropFirst() {
            let slice = self[start...end]
            if try !isMember(slice, self[end]) {
                result.append(self[start..<end])
                start = end
            }
        }
        
        if start != self.endIndex {
            result.append(self[start..<self.endIndex])
        }
        
        return result
    }
}