VERY simple Haskell shell to C translator

routines.h

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>

int exec_command(const char**);

int exec_command(const char* cmd[]) {
    /*
     *  Executes specified command
     *
     *  Returns exit status of executed command, or, if command was killed by a
     *  signal, 128+signum, or -1 if fork() failed
     */
    pid_t pid = fork();
    if(pid == -1) {
        perror("Error in fork()");
        // returning -1 is bad, but what should I do?
        return 126;
    }

    if(pid) {
        int retval;
        waitpid(pid, &retval, 0);
        if(WIFEXITED(retval)) {
            return WEXITSTATUS(retval);
        } else {
            // killed by signal
            // return 128+number of signal that teminated our child
            return 128 + WTERMSIG(retval);
        }
    } else {
        execvp(cmd[0], (char * const*)cmd);
        perror("Error in execvp()");
        switch (errno) {
            case EACCES:
                _exit(127);
                break;

            default:
                _exit(126);
        }
    }

    return 0;
}

task1.hs

-- task1.hs
-- Task:
-- write a simple generator of C code (in Haskell)
--
-- Let's say you have a list of commands, each represented by a list of strings.
-- Write a Haskell function which would generate a complete C program executing
-- those commands.
--
-- As I said above, you might want to pull as much code as possible outside the
-- generator. To achieve this, create a C file ("library") with auxiliary
-- functions.

type Command = [String]
type C = String

genC :: [Command] -> C
genC (x:xs) = helper "" "" 0 (x:xs)
    where helper :: C -> C -> Int -> [Command] -> C
          helper definitions code n []     = "#include \"routines.h\"\nint main(){\n" ++ definitions ++ code ++ "}\n"
          helper definitions code n (x:[]) = helper (definitions ++ "const char* cmd" ++ show n ++ "[] = { " ++ createArray x ++ "};\nint retval;\n") (code ++ "retval = exec_command (cmd" ++ show n ++ ");\nreturn retval;\n") (n+1) []
          helper definitions code n (x:xs) = helper (definitions ++ "const char* cmd" ++ show n ++ "[] = { " ++ createArray x ++ "};\n") (code ++ "exec_command (cmd" ++ show n ++ ");\n") (n+1) xs

          createArray :: Command -> C
          createArray (x:[]) = "\"" ++ x ++ "\", NULL"
          createArray (x:xs) = "\"" ++ x ++ "\", " ++ createArray xs
genC _      = ""

main = putStr (genC [["ping", "-c1", "google.com"], ["date"], ["tuch", "example.file"], ["ncal"], ["echo", "Hello, world!"]])