JSON Parser in Elixir

parser.ex

defmodule JSON do
  import String

  def parse( content ) do
    case parse_content(content) do
      { value, "" } -> value
      { _, _ } -> raise "crap"
    end

  end

  def parse_content( << m,  rest :: binary >> ) when m in ?0..?9, do: parse_number << m, rest :: binary >>
  def parse_content( << ?", rest :: binary >> ), do: rest |> parse_string 
  def parse_content( << ?{, rest :: binary >> ), do: lstrip(rest) |> parse_object 
  def parse_content( << ?[, rest :: binary >> ), do: lstrip(rest) |> parse_array

  def parse_string( << c, rest :: binary >> ), do: rest |> parse_string [c]
  def parse_string( << ?", rest :: binary >>, acc ), do: { to_string(Enum.reverse(acc)), rest }
  def parse_string( << c, rest :: binary >>, acc ), do: rest |> parse_string [c | acc]

  def parse_number( << m, rest :: binary >> ), do: rest |> parse_number [m]
  def parse_number( << ?., rest :: binary >>, acc ), do: rest |> parse_float [ "." | acc ]
  def parse_number( << m, rest :: binary >>, acc ) when m in ?0..?9, do: rest |> parse_number [ m | acc ]
  def parse_number( << rest :: binary >>, acc ), do: { Enum.reverse(acc) |> to_string |> String.to_integer, rest }

  def parse_float( << m, rest :: binary >>, acc ) when m in ?0..?9, do: rest |> parse_float [ m | acc ]
  def parse_float( << rest :: binary >>, acc ), do: { to_string(Enum.reverse(acc)) |> String.to_float, rest }

  def parse_array( content ), do: parse_array([], content)
  def parse_array( acc, << rest :: binary >> ) do
    { value, rest } = parse_content rest

    acc = [ value | acc ]

    case lstrip(rest) do
      << ?], rest :: binary >> -> { Enum.reverse(acc), rest }
      << ?,, rest :: binary >> -> parse_array acc, lstrip(rest)
    end
  end

  def parse_object( content ), do: parse_object(%{}, content)
  def parse_object( acc, << rest :: binary >> ) do
    { key, rest } = parse_content rest
    { value, rest } = lstrip(rest) |> parse_object_value

    acc = Map.put acc, key, value

    case lstrip(rest) do
      << ?}, rest :: binary >> -> { acc, rest }
      << ?,, rest :: binary >> -> parse_object acc, lstrip(rest)
    end
  end

  def parse_object_value( << ?:, rest :: binary >> ), do: lstrip(rest) |> parse_object_value
  def parse_object_value( rest ), do: parse_content rest
end

test = fn content -> 
  val = JSON.parse(content) 
  IO.puts "-----------------"
  IO.puts "#{content} =>"
  IO.inspect val
end

test.("\"asdf\"")
test.("0")
test.("1")
test.("10")
test.("18")
test.("1.8")
test.("{ \"a\": \"b\" }")
test.("{ \"x\": 1 }")
test.("{ \"q\": \"r\", \"s\": 10 }")
test.("{ \"q\": \"r\", \"s\": \"10\" }")
test.("{ \"q\": \"r\", \"s\": { \"t\": 99 } }")
test.("[1]")
test.("[1,2]")
test.("[1,2,3]")
test.("{ \"Ages\": [ 6.5, 5, 1, 1 ] }")
test.("{ \"Family\": [ { \"name\": \"Ryan\" }, { \"name\": \"Ben\" } ] }")

family = JSON.parse("{ \"Family\": [ { \"name\": \"Ryan\" }, { \"name\": \"Ben\" } ] }")

Enum.each family["Family"], fn person -> IO.inspect person["name"] end

I know, this sketch is old,
but your code doesn't support negative numbers
Fix is simple: replace ?0..?9 to '0123456789-'
My fixed version https://gist.github.com/pinya/01fa6c490bef8100d55dc158235f6a75