    -- life.lua
    -- original by Dave Bollinger <DBollinger@compuserve.com> posted to lua-l
    -- modified to use ANSI terminal escape sequences
    -- modified to use for instead of while

    local write=io.write

    ALIVE="¥"	DEAD="þ"
    ALIVE="O"	DEAD="-"

    function delay() -- NOTE: SYSTEM-DEPENDENT, adjust as necessary
      for i=1,10000 do end
      -- local i=os.clock()+1 while(os.clock()<i) do end
    end

    function ARRAY2D(w,h)
      local t = {w=w,h=h}
      for y=1,h do
        t[y] = {}
        for x=1,w do
          t[y][x]=0
        end
      end
      return t
    end

    _CELLS = {}

    -- give birth to a "shape" within the cell array
    function _CELLS:spawn(shape,left,top)
      for y=0,shape.h-1 do
        for x=0,shape.w-1 do
          self[top+y][left+x] = shape[y*shape.w+x+1]
        end
      end
    end

    -- run the CA and produce the next generation
    function _CELLS:evolve(next)
      local ym1,y,yp1,yi=self.h-1,self.h,1,self.h
      while yi > 0 do
        local xm1,x,xp1,xi=self.w-1,self.w,1,self.w
        while xi > 0 do
          local sum = self[ym1][xm1] + self[ym1][x] + self[ym1][xp1] +
                      self[y][xm1] + self[y][xp1] +
                      self[yp1][xm1] + self[yp1][x] + self[yp1][xp1]
          next[y][x] = ((sum==2) and self[y][x]) or ((sum==3) and 1) or 0
          xm1,x,xp1,xi = x,xp1,xp1+1,xi-1
        end
        ym1,y,yp1,yi = y,yp1,yp1+1,yi-1
      end
    end

    -- output the array to screen
    function _CELLS:draw()
      local out="" -- accumulate to reduce flicker
      for y=1,self.h do
       for x=1,self.w do
          out=out..(((self[y][x]>0) and ALIVE) or DEAD)
        end
        out=out.."\n"
      end
      write(out)
    end

    -- constructor
    function CELLS(w,h)
      local c = ARRAY2D(w,h)
      c.spawn = _CELLS.spawn
      c.evolve = _CELLS.evolve
      c.draw = _CELLS.draw
      return c
    end

    --
    -- shapes suitable for use with spawn() above
    --
    HEART = { 1,0,1,1,0,1,1,1,1; w=3,h=3 }
    GLIDER = { 0,0,1,1,0,1,0,1,1; w=3,h=3 }
    EXPLODE = { 0,1,0,1,1,1,1,0,1,0,1,0; w=3,h=4 }
    FISH = { 0,1,1,1,1,1,0,0,0,1,0,0,0,0,1,1,0,0,1,0; w=5,h=4 }
    BUTTERFLY = { 1,0,0,0,1,0,1,1,1,0,1,0,0,0,1,1,0,1,0,1,1,0,0,0,1; w=5,h=5 }

    -- the main routine
    function LIFE(w,h)
      -- create two arrays
      local thisgen = CELLS(w,h)
      local nextgen = CELLS(w,h)

      -- create some life
      -- about 1000 generations of fun, then a glider steady-state
      thisgen:spawn(GLIDER,5,4)
      thisgen:spawn(EXPLODE,25,10)
      thisgen:spawn(FISH,4,12)

      -- run until break
      local gen=1
      write("\027[2J")	-- ANSI clear screen
      while 1 do
        thisgen:evolve(nextgen)
        thisgen,nextgen = nextgen,thisgen
        write("\027[H")	-- ANSI home cursor
        thisgen:draw()
        write("Life - generation ",gen,"\n")
        gen=gen+1
        if gen>2000 then break end
        --delay()		-- no delay
      end
    end

    LIFE(40,20)