Concurrent programming - Erlang

part1.erl

Demonstrates sequential programming in Erlang. Provides the following functions;

* fib(N)
* adjacent duplicates(L)
* deep_sum(L)
* concatenate_all(L)
* perimeter(Shape)
* permutations(L)

Running the functions

On the erlang console erl> c(part1). erl> part1:fib(6). erl> part1:adjacent duplicates([1, 1, 2, 2, 3, 3]). erl> part1:deep_sum([1, 2, 3, 4]). erl> part1:concatnate_all(["Trevor","is","happy"]). erl> part1:perimeter({circle, 3}). erl> part1:permutations([1, 2, 3]).

Running all tests

erl> part1:test().

dictionary_server.erl

Demonstrates process and message passing in Erlang. The dictionary server can be started and key-values can be inserted. Upon inserting key-values, the server provides functions to lookup and remove values based on a key. The following functions are available;

* start/0  - Starts the dictionary server process. If there is already a dictionary server running, 
             this function should fail, but it’s not important what error it returns. 
* stop/0   - Stops the dictionary server process if it’s running. If there is no dictionary server
             process running, this function has no effect.
* insert/2 - Takes two parameters, a key and a value, and adds the given key and its value
             to the dictionary. If the given key is already in the dictionary, the new value should
             replace the old value in the dictionary. This function returns ok after its work is done.
* remove/1 - Takes one parameter, a key, and removes the given key from the dictionary if
             it’s present. This function returns ok if the key was removed successfully, or notfound
             if the key was not in the dictionary.
* lookup/1 - Takes one parameter, a key, and finds the corresponding value in the dictionary.
             If the key is in the dictionary, this function returns the tuple {ok, Value}, where
             Value is the value associated with the key. If the key is not in the dictionary, this
             function returns notfound.
* clear/0  - Clears all keys and values out of the dictionary.
* size/0   - Returns an integer specifying the number of keys in the dictionary.

Running the dictionary server

Start the server

erl> dictionary_server:start().

Insert a key-value pair

erl> dictionary_server:insert(ab,"This is ab").

Look up a value for a given key

erl> dictionary_server:lookup(ab).

Check the size of the dictionary

erl> dictionary_server:size().

Remove a given key

erl> dictionary_server:remove(ab).

Clear all keys of the dictionary

erl> dictionary_server:size().

Stop the dictionary server

erl> dictionary_server:stop().

integer_list.erl & integer_finder.erl

Demonstrates an implementation of MapReduce in Erlang. integer_list module can be spawned multiple times with different set of integers. To spawn a process;

erl> Pid1 = integer_list:start([3,5,2,1,4]).
erl> Pid2 = integer_list:start([3,4,2,6,8,9]).

And then integer_finder can be used to apply a function on all numbers of all integer_list processes. To run a finder;

erl> Pids = [Pid1, Pid2].
erl> integer_finder:find_integers(Pids, fun(X) -> X > 2 end).

An integer_list process can be stopped as follows;

erl> integer_list:stop(Pid1).