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Codepagex is an  elixir library to convert between string encodings to and from
utf-8. Like iconv, but written in pure Elixir.

All the encodings are fetched from tables and conversion functions
are generated from these at compile time.

## Examples

The package is assumed to be interfaced using only the `Codepagex` module.

    iex> from_string("æøåÆØÅ", :iso_8859_1)
    {:ok, <<230, 248, 229, 198, 216, 197>>}

    iex> to_string(<<230, 248, 229, 198, 216, 197>>, :iso_8859_1)
    {:ok, "æøåÆØÅ"}

    iex> from_string!("æøåÆØÅ", :iso_8859_1)
    <<230, 248, 229, 198, 216, 197>>

    iex> to_string!(<<230, 248, 229, 198, 216, 197>>, :iso_8859_1)

When there are invalid byte sequences in a String or encoded binary, the
functions will not succeed. If you still want to handle these strings, you may
specify a function to handle these circumstances. Eg:

    iex> from_string("Hello æøå!", :ascii, replace_nonexistent("_"))
    {:ok, "Hello ___!", 3}

    iex> iso = "Hello æøå!" |> from_string!(:iso_8859_1)
    iex> to_string!(iso, :ascii, use_utf_replacement)
    "Hello ���!"

## Encodings

A full list of encodings is found by running `encoding_list/1`. 

The encodings are best supplied as an atom, or else the string is converted to
atom for you (but with a somewhat less efficient function lookup). Eg:

    iex> from_string("æøå", "ISO8859/8859-9")
    {:ok, <<230, 248, 229>>}

    iex> from_string("æøå", :"ISO8859/8859-9")
    {:ok, <<230, 248, 229>>}

For some encodings, an alias is set up for easier dispatch. The list of aliases
is found by running `aliases/1`. The code looks like: 

    iex> from_string!("Hello æøåÆØÅ!", :iso_8859_1)
    <<72, 101, 108, 108, 111, 32, 230, 248, 229, 198, 216, 197, 33>>

## Encoding selection

By default all ISO-8859 encodings and ASCII is included. There are a few more
available, and these must be specified in the `config/config.exs` file. The
specified files are then compiled. Adding many encodings may affect compilation
times, in particular for the largest ones.

To specify the encodings to use, add the following lines to your
`config/config.exs` and recompile:

    use Mix.Config
    config :codepagex, :encodings, [:ascii]

This will add only the ASCII encoding, as specified by it's shorthand alias.
Any number of encodings may be specified like this in the list. The list may
contain strings, atoms or regular expressions that match either an alias or a
full encoding name, eg:

    use Mix.Config
    config :codepagex, :encodings, [
      :ascii,           # by alias name
      ~r[iso8859]i,     # by a regex matching the full name
      "ETSI/GSM0338",   # by the full name as a string
      :"MISC/CP856"     # by a full name as an atom

The encodings that are known to require very long compile times are:



- A few encodings are not yet supported for different reasons. In particular
  the asian and arab ones with left-right and up-down variations.
- Test Elixir function specs