CellKind = enum
  ckEmpty,                  ## no value in the cell
  ckText,                   ## plain text
  ckNumber,                 ## numeric value as float64
  ckBool,                   ## boolean
  ckDate,                   ## calendar date/time
  ckDuration,               ## time span in seconds
  ckFormula,                ## formula cell (display text or a marker)
  ckError                    ## cell that failed to decode or holds an error

CellValue = object
  case kind*: CellKind
  of ckEmpty:
    nil
  of ckText:
    text*: string
  of ckNumber:
    number*: float64
  of ckBool:
    boolean*: bool
  of ckDate:
    date*: DateTime
  of ckDuration:
    durationSeconds*: float64
  of ckFormula:
    formula*: string
  of ckError:
    error*: string