[Haskell-cafe] Baffled by Disk IO

I have run into a baffling distinction between the behavior of GHCi and the compiled binary from GHC. I suspect it's something pretty stupid on my part. I have the following test program import Matrix main = let f1 = bRgauss 4 3 f2 = bRgauss 3 2 fu = f1 *. f2 in bsave "fumat" fu ---------------------------------- The type signature of bsave is -- | save a matrix to a file bsave :: String -> m -> IO() bsave str z = do k <- matindx z withCString str (\x -> bmsave x k) and bmsave is a C routine that does a simple write to disk using fprintf. If I compile using GHC and run this as test.exe it does absolutely nothing, no file is actually saved. In fact no file is saved even if I try to print components of fu in the IO monad. Whereas if I load it into GHCi and run main, everything works as expected. Well sort of. Apparently everytime I extract something out of fu and use it in an IO monad it executes all the IO actions in fu, so it's easy to get unwanted behavior with incautious use.