Erlang libraries

Source: Elixir guide, Erlang libraries.

Elixir and Erlang interoperate directly. Elixir discourages wrapping Erlang libraries and just calls them. Erlang module names are lowercase atoms, Elixir's are capitalized aliases (which are atoms too), and calls work the same way:

String.first("hello")    #=> "h"
:binary.first("hello")   #=> 104

Common Erlang modules with no Elixir equivalent.

:binary

String works on UTF-8 text. :binary works on raw bytes:

String.to_charlist("Ø")   #=> [216]         (a code point)
:binary.bin_to_list("Ø")  #=> [195, 152]    (the bytes)

Formatted output

Elixir has no printf. Use :io.format/2 (to the terminal) or :io_lib.format/2 (to iodata). Format specifiers differ from C's:

:io.format("Pi is approximately given by:~10.3f~n", [:math.pi])
#=> Pi is approximately given by:     3.142

:crypto

Hashing, signatures, encryption:

Base.encode16(:crypto.hash(:sha256, "Elixir"))

:crypto isn't part of the :kernel or :stdlib applications, so list it in mix.exs:

def application do
  [extra_applications: [:crypto]]
end

The application a module belongs to is shown under the Erlang logo in its docs sidebar.

:digraph

Directed graphs with shortest-path and cycle algorithms:

digraph = :digraph.new()
[v0, v1, v2] = for c <- [{0.0, 0.0}, {1.0, 0.0}, {1.0, 1.0}], do: :digraph.add_vertex(digraph, c)
:digraph.add_edge(digraph, v0, v1)
:digraph.add_edge(digraph, v1, v2)
:digraph.get_short_path(digraph, v0, v2)
#=> [{0.0, 0.0}, {1.0, 0.0}, {1.0, 1.0}]

Three vertices, two edges, one shortest path.

:digraph changes the graph in place. That's possible because it's built on ETS tables.

ETS

:ets stores large data (in memory) and :dets stores it on disk. A table holds tuples, and works as a small database, key-value store or cache. By default tables are protected: only the owner process writes, anyone can read. Functions modify the table as a side effect.

Protected: one writer, many readers.

table = :ets.new(:ets_test, [])
:ets.insert(table, {"China", 1_374_000_000})
:ets.insert(table, {"India", 1_284_000_000})

:math, :queue, :rand, :zip and :zlib

:math covers trigonometry, exponentials and logarithms (:math.sin/1, :math.exp/1, :math.log/1).

:queue is an efficient double-ended FIFO queue:

First in, first out. An empty queue returns :empty.

q = :queue.new
q = :queue.in("A", q)
q = :queue.in("B", q)
{value, q} = :queue.out(q)   # value = {:value, "A"}

:rand gives random values (:rand.uniform/0, :rand.uniform(6)) and seeding (:rand.seed/2). :zip reads and writes ZIP files, :zlib does zlib compression (:zlib.compress/1 and :zlib.uncompress/1).

Learning Erlang

The guide points to Erlang Syntax: A Crash Course (Elixir next to Erlang), the Erlang course on erlang.org, and Learn You Some Erlang for Great Good!.