Dim As String sComma, sString, sFlatter
Dim As Short siCount

sString = "[[1], 2, [[3,4], 5], [[[]]], [[[6]]], 7, 8 []]"

For siCount = 1 To Len(sString)
    If Instr("[] ,", Mid(sString, siCount, 1)) = 0 Then
        sFlatter += sComma + Mid(sString, siCount, 1)
        sComma = ", "
    End If
Next siCount

Print "["; sFlatter; "]"
Sleep