erlang

Priority receive in Erlang can easily be implemented as follows: prio() -> receive {priority, X} -> X after 0 -> receive X -> X end end. I am reading a paper called Priority Messaging made Easy in which they describe the following problem: The main problem with the [code] example [above], is that we do not take into consideration that when evaluation is resumed from the inner blocking receive we may have more than one message in the mailbox. In a worst case scenario, all but the first, of potentially a huge number, of elements could be priority messages. In this scenario we would actually have

I have an mnesia table with three fields, i, a and b, created using the record -record(rec, {i, a,b}). Now I insert a row into the table as: mnesia:transaction( fun() -> mnesia:write("T", #rec{i=1, a=2, b=3}, write) end ). Now what do I do if I want to update this row, and change only the value of a to 10, while leaving i and b with the same values? Is there any SQL equivalent like " UPDATE T SET a=10 WHERE i=1 "? If I do something like this: mnesia:transaction( fun() -> mnesia:write("T", #rec{i=1, a=10}, write) end ) The row is stored as: {rec,1,10,undefined} The value of this function will

I to need modify the values {place} and {other_place} in the op record. #op{ action = [walk, from, {place}, to, {other_place}], preconds = [[at, {place}, me], [on, floor, me], [other_place, {place}, {other_place}]], add_list = [[at, {other_place}, me]], del_list = [[at, {place}, me]] } But erlang don´t allow modifying variables. Is there a data type for that? erlang doesn't let you modify variables it is true. But nothing prevents you from making modified copies of a variable. Given your record: Rec = #op{ action = [walk, from, {place}, to, {other_place}], preconds = [[at, {place}, me], [on,

When I try to set a relative code path in a escript with -pz like this #!/usr/bin/env escript %% -*- erlang -*- %%! -pz ../dir-of-some-beams The path is interpreted relative to the directory from where I run the escript from, which renders it useless for setting the path relative to the script location. My current "workaround" is using a absolute path which is annoying since all this is part of a repository and I don't want it to be location dependent. So how can I set the code path relative to the directory the escript is located in? Just found it out myself: At the beginning of main add code

I'm developing a real time chat app. After searching around for a while, I found Ejabberd and Erlang is a good option. The question is the Ejabberd is not providing all the functions I need. I need some custom features such as location based matching and anonymous login. So how to development custom functions on top of Ejabberd? write modules for it? or develop another standalone server app (web or other kind of server app) to interact with it? update: another concern is the way we add custom functions/features should be scalable. You can write your custom modules which hook up to events in

As the question said: What benefits brings using the OTP design principles when developing with erlang? (I am developing a server which will just receive commands and send responses) OTP is a battle-hardened set of design elements and idioms used in the creation of, as Jonas said, fault-tolerant systems among other things (like flexibility, live updates, etc.). In brief you want to use it for these environments, or environments that may grow into these, because a lot of the blood, sweat and tears of creating reliable, stable systems in Erlang is baked into the OTP behaviours and architecture.

安装参考：官方文档 http://www.rabbitmq.com/install-debian.html#apt Installing Erlang Packages Signing Key In order to use the repository, add a key used to sign RabbitMQ releases to apt-key: wget -O - 'https://dl.bintray.com/rabbitmq/Keys/rabbitmq-release-signing-key.asc' | sudo apt-key add - This will instruct apt to trust packages signed by that key. Source List File As with all 3rd party Apt (Debian) repositories, a file describing the repository must be placed under the /etc/apt/sources.list.d/ directory. /etc/apt/sources.list.d/bintray.erlang.list is the recommended location. The file should have