struct stringlist *scan;
int fd[2];

/*
     SCHEME:
        STDIN --> O --> O --> O --> STDOUT
*/
int eval(tree,inport,outport)
     evptr tree;
     int inport, outport;
{

  if (tree->tag == PIPETAG) {
    pipe(fd);

    eval(tree->son.left, 0, 1);
    eval(tree->son.right, 1, 0);

  } else if (tree->tag == LEAF) {

    char **commands;
    int i=0;

    commands = (char**) malloc(10 * sizeof(char*));
    if (commands == NULL)
      exit(-1);

    for (scan = tree->leaf.data; scan != NULL; scan = scan->next) {
      commands[i] = scan->fname;
      i++;
    }
    commands[i] = NULL;

    //======================================================

    pid_t pid;

    pid = sfork();
    if (pid == 0) {
      printf("inport: %d outport: %d\n", inport, outport);

      if (inport == 0) {
        dup2(fd[WRITE_END], STDOUT_FILENO);
      } else if (inport != 0) {
        dup2(inport, STDIN_FILENO);
        //dup2(fd[WRITE_END], STDOUT_FILENO);
      }

      execvp(commands[0], commands);
      exit(1);
    }

    else {
      //close(fd[READ_END]);
      //close(fd[WRITE_END]);
      free(commands);
      wait(NULL);
    }
  } else if (tree->tag == NULLTAG) {

  } else if (tree->tag == EXITAG) {
    exit(0);
  } else {
    exit(1);
  }
};