$DERIVE(EXPRESSION) : FONCTION DÉRIVÉE

derive {
  if * !isin $$1 && / !isin $$1 && $chr(40) !isin $$1 && $chr(41) !isin $$1 {
    tokenize 32 $replace($replace($$1, -, +-, ¹, ^1, ², ^2, ³, ^3), ^+-, ^-)
    if ($left($$1, 1) == +) tokenize 32 $right($$1, $calc($len($$1) -1))
    if ($$1 isnum) return 0
    var %¥ = $numtok($$1, 43)
    var %? = 0
    while %? < %¥ {
      inc %?
      var %¤ = $gettok($$1, %?, 43)
      %¤ = $iif($left(%¤, 1) == x, 1) $+ %¤ $+ $iif($right(%¤, 1) == x, ^1)
      if %¤ !isnum {
        var %¢ = $remove($gettok(%¤, $numtok(%¤, 120), 120), ^)
        var %£ = $+(%£, +, $remove($calc(%¢ * $iif($gettok(%¤, 1, 120) != x, $v1, 1)) $+ x^ $+ $calc(%¢ -1), x^0, ^1))
      }    
    }
    return $replace($right(%£, $calc($len(%£) -1)), +-, -, 1x, x)
  }
}