Read books in parallel!

readbooks.c

#include <stdio.h>

void clean_eof_array(int eof_i, FILE **farr, int size) {
  fclose(farr[eof_i]);
  farr[eof_i] = NULL;
  for (int i = eof_i + 1; i < size && farr[i] != NULL; i++) {
    farr[i - 1] = farr[i];
    farr[i] = NULL;
  }
}

int main(const int argc, const char **argv) {
  FILE *file[10] = { 0 };
  for (int i = 1; i < argc; i++) {
    file[i - 1] = fopen(argv[i], "r");
  }

  int size = argc - 1;
  while (size > 0) {
    for (int i = 0; i < size; i++) {
      int c = fgetc(file[i]);
      if (feof(file[i])) {
        // also decrement i because the file array has been moved.
        clean_eof_array(i--, file, size--);
      } else {
        fputc(c, stdout);
      }
    }
  }

  return 0;
}

readbooks.scm

(use-modules (ice-9 binary-ports))

(define (main args)
  (let A ((open-files '())
          (filenames (cdr args)))
    (if (null? filenames)
        (let B ((left '())
                (right (reverse open-files)))
          (if (null? right)
              (if (not (null? left))
                  (B '() (reverse left)))
              (let* ((rhd (car right))
                     (rtl (cdr right))
                     (c (get-u8 rhd)))
                (if (eof-object? c)
                    (B left rtl)
                    (begin
                      (put-u8 (current-output-port) c)
                      (B (cons rhd left) rtl))))))
        (call-with-input-file (car filenames)
          (lambda (port) (A (cons port open-files)
                            (cdr filenames)))))))