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
<test.hs>
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.
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