{-# LANGUAGE OverloadedStrings #-}

{-# LANGUAGE ScopedTypeVariables #-}

{-# LANGUAGE TypeApplications #-}

module HsLua.Marshalling.Userdata

( pushIterator

) where

import Control.Monad (void)

import HsLua.Core as Lua

-- | Pushes three values to the stack that can be used in a generic for

pushIterator :: forall a e. LuaError e

=> (a -> LuaE e NumResults) -- ^ pusher for the values

-> [a] -- ^ list to iterate over lazily

-> LuaE e NumResults

pushIterator pushValues xs = do

-- push initial state

pushHaskellFunction nextItem

pushInitialState

pushnil

return (NumResults 3)

where

nextItem :: LuaE e NumResults

nextItem = do

props <- fromuserdata @[a] (nthBottom 1) statename

case props of

Nothing -> failLua

"Error in iterator: could not retrieve iterator state."

Just [] -> 2 <$ (pushnil *> pushnil) -- end loop

Just (y:ys) -> do

success <- putuserdata @[a] (nthBottom 1) statename ys

if not success

then failLua "Error in iterator: could not update iterator state."

else pushValues y >>= \case

0 -> nextItem -- keep going if nothing was pushed

n -> return n

statename :: Name

statename = "HsLua iterator state"

pushInitialState :: LuaE e ()

pushInitialState = do

newhsuserdata @[a] xs

void (newudmetatable statename)

setmetatable (nth 2)