Implementation of Run-length encoding algorithm in Erlang. Both encode and decode functions are provided. For more info see https://en.wikipedia.org/wiki/Run-length_encoding and http://rosettacode.org/wiki/Run-length_encoding - the latter has a couple of implementations in Erlang, but I like using lists:foldr/3 this way.

rle.erl

-module(rle).

-export([encode/1]).
-export([decode/1]).

encode(List) ->
    lists:flatten(lists:foldr(
        fun (Prev, [[Count, Prev]|Rest]) ->
                [[Count + 1, Prev]|Rest];
            (Current, Acc) ->
                [[1, Current]|Acc]
        end,
        [],
        List)).

decode(List) ->
    decode(List, []).

decode([], Acc) ->
    lists:reverse(Acc);
decode([Count|[Char|Rest]], Acc) ->
    AccNew = lists:append(lists:duplicate(Count, Char), Acc),
    decode(Rest, AccNew).