from algebraic effects to N-Barrelled CPS

n_cps.lua

-- support functions {{{
-- to find corresponding effect handler
local function lookup(h, eff, v)
  local effh = h[eff]

  if effh then
      return function(k)
        return effh(v, k)
      end
  else
    error(("handler for ``%s'' not found"):format(eff))
  end
end

local VALUE = "value"

-- to fetch value handler
local lookup_v = function(h, v)
  return function(k)
    return h[VALUE](v, k)
  end
end
--}}}

--[[
let r =
  print (
    handle (perform (Foo 5)) with
    | val y -> y * 20
    | effect (Foo x) k -> k (x * x)
    | effect (Bar b) k -> k (b - b)
  )
--]]

-- new effects
local Foo = "foo"
local Bar = "bar"

local r = (function (k0, h0)
  return (function(k1, h1)
    return k1(5)
  end)(function (v) -- let v = 5 in
    return --[[perform (Foo v) ]] lookup(h0, Foo, v)(function(res)
      return lookup_v(h0, res)(k0)
    end)
  end, h0)
end)(print,
     { [VALUE] = function(v, k) return k(v * 20) end
     , [Foo]   = function(x, k) return k(x + x) end
     , [Bar]   = function(b, k) return k(b - b) end })