[Q] About Unix Library of Ocaml

[Bomshik Kim <bskim@ropas.kaist.ac.kr>]

 Hello~ 
 I Have Some Questions About Unix Library

1) Why do these exceptions occur ?

---------------------------------------------------------- 
        Objective Caml version 2.04

# open Unix ;;
# let theSocket = socket PF_INET SOCK_STREAM 0 ;;
val theSocket : Unix.file_descr = <abstr>
# let theSocket = socket PF_INET SOCK_DGRAM 0 ;;
val theSocket : Unix.file_descr = <abstr>
# let theSocket = socket PF_INET SOCK_RAW 0 ;;
Uncaught exception: Unix.Unix_error(1, "socket", "")
# let theSocket = socket PF_INET SOCK_SEQPACKET 0 ;;
Uncaught exception: Unix.Unix_error(45, "socket", "")
# 
----------------------------------------------------------

2) What is the differences of 4 socket_type ?
 Stream socket, Datagram socket, Raw socket, Sequenced packets socket

3) Error with using connection function  

 Could you let me know the error code(63)
 and why does this error occur? 

-----------------------------------------------------------
        Objective Caml version 2.04

# open Unix ;;
# let addr = inet_addr_of_string "***.***.***.***" ;;
val addr : Unix.inet_addr = <abstr>
# let socketAddr = ADDR_INET( addr , 21 ) ;;
val socketAddr : Unix.sockaddr = ADDR_INET (<abstr>, 21)
# let theSocket = socket PF_INET SOCK_STREAM 0 ;;
val theSocket : Unix.file_descr = <abstr>
# connect theSocket socketAddr ;;
Uncaught exception: Unix.Unix_error(63, "connect", "")
-----------------------------------------------------------


4) Where can I get more specific information(examples, docs, papers) 
  about ocaml library especially unix library 
  (in order to design & implement bigger network library of ocaml 
   for building web-server, web-browser etc... )

@ thank you 
-bskim@ropas.kaist.ac.kr