GHCJS: setTimeout($c, $1);: invalid placeholder, check function type: "$c"

Question

I've installed VM as suggested, and now reading this article. Now I'm at the very beginning and looking at FFI example. I have missing ffi.jsexe/ folder (within ghcjs-examples/weblog/ffi) and tried to compile it by myself. But it fails with following error:

setTimeout($c, $1);: invalid placeholder, check function type: "$c"

Here is quick reminder what we have in ffi.hs:

{-# LANGUAGE JavaScriptFFI, CPP #-}

module Main where

#ifdef __GHCJS__
foreign import javascript unsafe "document.write($1+'<br/>');" writeNumber :: Int -> IO ()
foreign import javascript safe   "setTimeout($c, $1);"         delay       :: Int -> IO ()
#else
writeNumber = error "writeNumber: only available from JavaScript"
delay = error "delay: only available from JavaScript"
#endif

main :: IO ()
main = mapM_ (\x -> writeNumber x >> delay 1000) [1..1000]

Sorry, I'm new to Haskell and FP at all, so some thing for me is just alike magic for now. I've replaced $c with null because it makes sense since delay itself have only one argument, thus there will be no code executed. So it compiles, but when I opened it in a browser all numbers are printed instantly. Also I have a little pre-question. setTimeout return some handler (integral value), and takes a callback function and time in ms, right? So why the delay have this type signature Int -> IO () instead of, say, IO () -> Int -> IO Int?

And the main question is why it rejects to compile? Is this example outdated and something have been changed in ghcjs itself?

GHC   7.7.2
GHCJS 0.1.0

Answer 1

On the current VM, if I write interruptible instead safe in the foreign import, it works.