declare Length Take Drop Append Member Position
fun {Length List}
   case List of _|Tail then (1 + {Length Tail}) else 0 end
end

fun {Take (Head|Tail) Count}
   if Count > 0 then (Head|{Take Tail (Count - 1)}) else nil end
end

fun {Drop (Head|Tail) Count}
   if Count > 0 then {Drop Tail (Count - 1)} else Head|Tail end
end

fun {Append List Other}
   case List 
   of X|nil then X|Other
   [] Head|Tail then Head|{Append Tail Other}
   else nil end
end

fun {Member (Head|Tail) Element}
   if Tail == nil 
      then false 
   else 
      if Head == Element 
         then true 
      else 
         {Member Tail Element} 
      end
   end
end

fun {Position (Head|Tail) Element}
   if Head == Element 
      then 0 % 0-indexed
   else 
      1 + {Position Tail Element}
   end
end