Heck, you don't even need that. Put this in a file named "Hello.hs":
module Hello where
main = print "Hello world!"
and run "ghc -fvia-C -keep-hc-files Hello.hs". Compilation may fail with linker errors, but today we don't care about that. We just want to look at the resulting Hello.hc file, which is the C representation of the Haskell, and generally looks like:
I admit to basing this on nothing more than a gut feeling, but a "sufficiently smart decompiler" seems even less plausible than a "sufficiently smart compiler".