I'm trying to call Socket.select to deal with some sockets. It seems like the following minimal snippet from my code should work...
fun descs ss = map Socket.sockDesc ss
fun selecting server clients =
let val { ss, ws, cs } = Socket.select {
rds = descs [server],
wds = descs [],
exs = descs clients,
timeout = (SOME (Time.fromSeconds 10))
}
in
(ss, ws, cs)
end
... but doesn't when I evaluate it in SML/NJ:
Standard ML of New Jersey v110.76 [built: Thu Feb 19 00:37:13 2015]
- fun descs ss = map Socket.sockDesc ss ;;
[autoloading]
[library $SMLNJ-BASIS/basis.cm is stable]
[autoloading done]
val descs = fn : ('a,'b) Socket.sock list -> Socket.sock_desc list
- fun selecting server clients =
let val { ss, ws, cs } = Socket.select {
rds = descs [server],
wds = descs [],
exs = descs clients,
timeout = (SOME (Time.fromSeconds 10))
}
in
(ss, ws, cs)
end ;;
= = = = = = = = = [autoloading]
[autoloading done]
stdIn:3.13-8.7 Error: operator and operand don't agree [tycon mismatch]
operator domain: {exs:Socket.sock_desc list, rds:Socket.sock_desc list,
timeout:Time.time option, wrs:Socket.sock_desc list}
operand: {exs:Socket.sock_desc list, rds:Socket.sock_desc list,
timeout:Time.time option, wds:Socket.sock_desc list}
in expression:
Socket.select
{rds=descs (server :: nil),wds=descs nil,exs=descs clients,
timeout=SOME (Time.fromSeconds 10)}
-
-
Could anyone point out what I'm doing wrong?
(Thanks to bgates from #sml for pointing me in the right direction here)
Two problems with the above. Firstly, I had a typo in the constructor name in the call to Socket.select.
...
rds = descs [server],
wrs = descs [], (* `wrs` instead of `wds` here *)
exs = descs clients,
...
Secondly, when pattern-matching on records, you must use the slot-names of the record rather than arbitrary symbols. So
...
let val { ss, ws, cs } = Socket.select {
...
should actually be
...
let val { rds, wrs, exs } = Socket.select {
...
With those changes...
Standard ML of New Jersey v110.76 [built: Thu Feb 19 00:37:13 2015]
- fun descs ss = map Socket.sockDesc ss ;;
[autoloading]
[library $SMLNJ-BASIS/basis.cm is stable]
[autoloading done]
val descs = fn : ('a,'b) Socket.sock list -> Socket.sock_desc list
- fun selecting server clients =
let val { rds, exs, wrs } = Socket.select {
rds = descs [server],
wrs = descs [],
exs = descs clients,
timeout = (SOME (Time.fromSeconds 10))
}
in
(rds, wrs, exs)
end ;;
= = = = = = = = = [autoloading]
[autoloading done]
val selecting = fn
: ('a,'b) Socket.sock
-> ('c,'d) Socket.sock list
-> Socket.sock_desc list * Socket.sock_desc list *
Socket.sock_desc list
-