Racket mmap

gistfile1.txt

(define-cstruct _mmap_obj ([fd _int]
                           [loaded_size _uint32]
                           [content _pointer]))

(define-cstruct _wp_index ([pathname_base _pointer]
                           [num_segments _uint16]
                           [sizeof_segments _uint16]
                           [docid_offsets _pointer]
                           [segments _pointer]
                           [open _uint8]
                           [indexinfo _mmap_obj]))
(define-whistlepig wp_index_create (_fun [m : (_ptr o (_ptr o _wp_index))] _string -> [n : _pointer] -> (if (not n) m n)))

(define (add-source-files)
  (define source-files (filter
                        (lambda (f) (string-index f (string->char-set ".rkt")))
                        (map path->string (directory-list))))
  (map
   (lambda (file-path)
     (begin
       (define index (wp_index_create "index"))
       (define entry (wp_entry_new))
       (define f (fopen file-path "r"))
       (wp_entry_add_file entry "body" f)
       (wp_index_add_entry index entry)
       (wp_entry_free entry)
       (fclose f)
       (printf "Added source files in CWD to the index\n")))
   source-files))

Error:
racket(25776,0x7fff78e64180) malloc: *** mmap(size=9223372036854775808) failed (error code=12)