Hidden Features of Erlang [closed]

Answer 1

You can hide an Erlang node by starting it with:

erl -sname foo -hidden

You can still connect to the node, but it won't appear in the list returned by nodes/0.

Answer 2

user_default.erl - you can build your own shell builtins by having a compiled user_default.beam in your path which can be pretty nifty

Answer 3

The magic commands in the shell. The full list is in the manual, but the ones I use most are:

• f() - forget all variables
• f(X) - forget X
• v(42) - recall result from line 42
• v(-1) - recall result from previous line
• e(-1) - reexecute expression on previous line
• rr(foo) - read record definitions from module foo
• rr("*/*") - read record definitions from every module in every subdirectory
• rp(expression) - print full expression with record formating

Answer 4

It is possible to define your own iterator for QLC to use. For example, a result set from an SQL query could be made into a QLC table, and thus benefit from the features of QLC queries.

Besides mnesia tables, dets and ets have the table/1,2 functions to return such a "Query Handle" for them.

Answer 5

The gen___tcp and ssl sockets have a {packet, Type} socket option to aid in decoding a number of protocols. The function erlang:decode_packet/3 has a good description on what the various Type values can be and what they do.

Together with a {active, once} or {active, true} setting, each framed value will be delivered as a single message.

Examples: the packet http mode is used heavily for iserve and the packet fcgi mode for ifastcgi. I can imagine that many of the other http servers use packet http as well.