jhc-Cさんはforever <http://hackage.haskell.org/packages/archive/base/latest/doc/html/Control-Monad.html#v:forever> をgotoループに変換する。

jhc-Cした後.c

static void A_STD
ftheMain(gc_t gc)
{
        fPrelude_IO_putStr(gc,PROMOTE(c375));
        saved_gc = gc;
        (void)jhc_utf8_putchar((int)10);
        fR$__fControl_Monad_forever__57:;
        {   wptr_t v9;
            fPrelude_IO_putStr(gc,PROMOTE(c377));
            v9 = fPrelude_IO_getLine(gc);
            {   wptr_t v100000;
                wptr_t v100004;
                gc_frame0(gc,1,v9);
                v100000 = fData_Map_fromList(gc,PROMOTE(c392));
                v100004 = fData_Map_lookup(gc,v9,v100000);
                if (SET_RAW_TAG(CJhc_Type_Basic_Nothing) == v100004) {
                    wptr_t v20;
                    v20 = fPrelude_IO_putStr(gc,v9);
                    demote(v20);
                } else {
                    sptr_t v36;
                    /* ("CJhc.Type.Basic.Just" ni36) */
                    v36 = ((struct sCJhc_Type_Basic_Just*)v100004)->a1;
                    wptr_t v100006 = eval(gc,v36);
                    bapply__15390(gc,v100006);
                }
                goto fR$__fControl_Monad_forever__57;
            }
        }
        return;
}

jhc通る前.hs

main :: IO ()
main = do
  putStrLn "Haskell bootmenu"
  forever $ do
    putStr "> "
    s <- getLine
    fromMaybe (putStr s) $ Map.lookup s commands

Haskell元ソースコードは https://gitorious.org/metasepi/netbsd-arafura/blobs/arafura/metasepi-arafura/sys/arch/i386/stand/boot/Boot2Ara.hs のあたり。