Lazy lists in lua, kinda sorta really useless

lazy.lua

#!/usr/bin/env lua5.2

local cryield = coroutine.yield
local crwrap = coroutine.wrap

function map(f, xs)
   return crwrap(function()
      for v in xs do
         cryield(f(v))
      end
   end)
end

function takeWhile(p, xs)
   return crwrap(function()
      for v in xs do
         if not p(v) then
            break
         end
         cryield(v)
      end
   end)
end

function take(n, xs)
   return crwrap(function()
      local i = 1
      for v in xs do
         if i > n then
            break
         end
         i = i + 1
         cryield(v)
      end
   end)
end

function drop(n, xs)
   return crwrap(function()
      local i = 1
      for v in xs do
         if i > n then
            cryield(v)
            break
         end
         i = i + 1
      end
      for v in xs do
         cryield(v)
      end
   end)
end

function dropWhile(f, xs)
   return crwrap(function()
      for v in xs do
         if not f(v) then
            cryield(v)
            break
         end
      end
      for v in xs do
         cryield(v)
      end
   end)
end

function range(a, b)
   return crwrap(function()
      for i = a, b do
         cryield(i)
      end
   end)
end

function list(...)
   local l = {...}
   return crwrap(function()
      for _, i in ipairs(l) do
         cryield(i)
      end
   end)
end

function cons(x, xs)
   return crwrap(function()
      cryield(x)
      for v in xs do
         cryield(v)
      end
   end)
end

function head(xs)
   return xs()
end

function tail(xs)
   xs()
   return xs
end

function length(xs)
   local l = 0
   for _ in xs do
      l = l + 1
   end
   return l
end

function concat(xs, ys)
   return crwrap(function()
      for v in xs do cryield(v) end
      for v in ys do cryield(v) end
   end)
end

-- [start,step,...]
function generate(start, step, end_)
   step = step or 1
   return crwrap(function()
      local n = 1
      while end_ == nil or start <= end_ do
         cryield(start)
         start = start + step * n
         n = n + 1
      end
   end)
end

function repeat_(val)
   return crwrap(function()
      while true do
         cryield(val)
      end
   end)
end

function foldr(f, z, xs)
   local r = z
   for v in xs do
      r = f(r, v)
   end
   return r
end

print(foldr(function(x,z) print(x, z) return x+z end,0,drop(1,
         dropWhile(function(x) return x<10 end,
            take(10,
               takeWhile(function(x) return x<40 end,
                  map(function(x) return x*2 end,
                     tail(cons("moo",
                        generate(0))))))))))