As a side note to what has already been mentioned, cpanm is faster than cpan, especially on systems with limited/slow resources (e.g. Raspberry Pi/embedded systems). The deprecated scandeps method may be of interest, but it isn't complete for reasons stated in existing responses:

cpanm --scandeps AnyEvent::WebSocket::Server


=> Found dependencies: AnyEvent::Handle, AnyEvent::Socket
AnyEvent-WebSocket-Server-0.10
\_ Test-Memory-Cycle-1.06
 \_ Devel-Cycle-1.12
 \_ PadWalker-2.5
\_ AnyEvent-WebSocket-Client-0.54
 \_ Protocol-WebSocket-0.26
 \_ PerlX-Maybe-1.202
 \_ Canary-Stability-2013
 \_ AnyEvent-7.17
 \_ AnyEvent-Connector-0.03
[download]

See also App::cpm.