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Typed Lua Class System

The following code gives a sneak peak of the Lua Class system. While this code typechecks, the class system is still in the process of being debugged.

``

interface IComparable<-T> --returns true if self is less than or equal to argument method leq : (T) => (boolean) end

--cartesian product of X and Y, using componentwise ordering class ComparablePair< X <: IComparable, Y <: IComparable > implements IComparable< ComparablePair<X, Y> > const x : X const y : Y

constructor new(x : X, y : Y) self.x = x self.y = y end

method leq(a : ComparablePair<X, Y>) : boolean return self.x:leq(a.x) and self.y:leq(a.y) end end

local function quicksort< X <: IComparable >(x : {X}) local function swap(i : integer, j : integer) local temp = x[i] x[i] = x[j] x[j] = temp end

local function partition(lo : integer, hi : integer) : integer local pivot = x[hi]

--index after the contiguous chunk of all values 
--encountered so far that are less than the pivot
local z = lo

for i=2,#x do
  local xi = x[i]
  if xi then
    if pivot then 
      if xi:leq(pivot) then
        swap(i,z)
        z = z + 1
      end
    end
  else
    error("array should be non-nil over its range")
  end
end 

return z

end

local function sort(lo : integer, hi : integer) if hi - lo <= 1 then return end

local p = partition(lo, hi)
sort(lo,p-1)
sort(p+1,hi)

end

sort(1,#x) end

class Factory implements IComparable cost : number

constructor new(cost : number) self.cost = cost end

method leq(other : Factory) : boolean return self.cost <= other.cost end end

class Office implements IComparable cost : number

constructor new(cost : number) self.cost = cost end

method leq(other : Office) : boolean return self.cost <= other.cost end
end

class CompanyBuildings extends ComparablePair<Factory,Office> constructor new(f : Factory, o : Office) super.new(f,o) end end

local f = class(Factory) local o = class(Office) local cb = class(CompanyBuildings)

local factories : {Factory} = { f.new(1), f.new(2), f.new(3) } local offices : {Office} = { o.new(5), o.new(1), o.new(4) } local buildingsets : {CompanyBuildings} = { cb.new( f.new(1), o.new(5) ), cb.new( f.new(2), o.new(1) ), cb.new( f.new(3), o.new(4) ) } ``