Getting a simple Haskell HsLua example to work

The HsLua examples on the Haskell Wiki are broken (dostring and dofile are not defined). Looks like the API has changed since the examples were written.

However I have been trying to modify the examples to match the current API and not getting much success. Here's a program that should really work!

main = do
    l <- Lua.newstate
    Lua.openlibs l
    Lua.loadfile l "configfile.lua"
    [name,pwd] <- Lua.callfunc l "getuserpwd" "mail.google.com"
    putStrLn name
    Lua.close l

However, this doesn't even compile, giving me this strange error message -

No instance for (Lua.StackValue [String])
  arising from a use of `Lua.callfunc'
Possible fix:
  add an instance declaration for (Lua.StackValue [String])
In a stmt of a 'do' expression:
    [name, pwd] <- Lua.callfunc l "getuserpwd" "mail.google.com"
In the expression:
  do { l <- Lua.newstate;
       Lua.openlibs l;
       Lua.loadfile l "configfile.lua";
       [name, pwd] <- Lua.callfunc l "getuserpwd" "mail.google.com";
       .... }
In an equation for `main':
    main
      = do { l <- Lua.newstate;
             Lua.openlibs l;
             Lua.loadfile l "configfile.lua";
             .... }

While the content of the file configfile.lua probably doesn't matter (because the haskell code doesn't even compile), it is as below (same as on the wiki page) -

function getuserpwd (site)
  local cookies = { ["www.ibm.com"] = {"joe", "secret"}
                  , ["www.sun.com"] = {"hoe", "another secret"}
                  }
  if cookies[site] then
    return cookies[site]
  elseif site:match("[.]google[.]com$") then
    return {"boss", "boss"}
  else
    return { os.getenv("USER") or "God"
           , os.getenv("PWD")  or "dontdisturb" }
  end
end

Could someone please provide me with a working example of Haskell->Lua and Lua->Haskell calls?

Edit

Okay I changed the type of the return value to a String (from the earlier array of String), and that program does compile! However it now fails at runtime. Here's the modified program -

main = do
    l <- Lua.newstate
    Lua.openlibs l
    Lua.loadfile l "configfile.lua"
    Lua.callfunc l "getuserpwd" "mail.google.com" >>= putStrLn
    Lua.close l

And here's configfile.lua -

function getuserpwd (site)
  return "bo开发者_高级运维ss"
end

And the runtime error message is as follows -

**** Exception: user error (attempt to call a nil value)

---

You have to execute loaded Lua chunk prior to calling any functions:

main = do
    l <- Lua.newstate
    Lua.openlibs l
    Lua.loadfile l "configfile.lua"
    Lua.call l 0 0
    Lua.callfunc l "getuserpwd" "mail.google.com" >>= putStrLn
    Lua.close l

Method dofile was a wrapper for loadfile and call, I don't know reasons for removing it.

Edit. This code calls function that returns table and iterates over it. It is based on this traversal example. I am not sure how to do it via callfunc.

import qualified Scripting.Lua as Lua
import Control.Monad.Loops
import Data.Maybe

print_table l = do
    Lua.pushnil l
    whileM_ (Lua.next l 1) (Lua.tostring l (-1) >>= putStrLn >> Lua.pop l 1)

main = do
  l <- Lua.newstate
  Lua.openlibs l
  Lua.loadfile l "configfile.lua"
  Lua.call l 0 0
  Lua.getglobal l "getuserpwd"
  Lua.pushstring l "mail.google.com"
  Lua.call l 1 (-1) -- calls function without Haskell extensions
  print_table l
  Lua.close l

It turns out that HsLua implementation is a very simple wrapper and there are no suitable Haskell bindings for Lua tables.

---

additionaly

dostring + dofile utils:
https://github.com/ajnsit/luautils
http://hackage.haskell.org/package/luautils

luaDoString :: Lua.LuaState -> String -> IO Int
result <- luaDoString l "return 2^3"