philomena/lib/search/float_parser.ex

defmodule Search.FloatParser do
  import NimbleParsec

  defp to_number(input), do: Search.Helpers.to_number(input)
  defp range(input), do: Search.Helpers.range(input)

  space =
    choice([string(" "), string("\t"), string("\n"), string("\r"), string("\v"), string("\f")])
    |> ignore()

  fuzz =
    string("~")
    |> ignore()

  unsigned_float =
    ascii_string([?0..?9], min: 1)
    |> optional(ascii_char('.') |> ascii_string([?0..?9], min: 1))
    |> reduce({List, :to_string, []})
    |> reduce(:to_number)

  float =
    optional(ascii_char('-+'))
    |> ascii_string([?0..?9], min: 1)
    |> optional(ascii_char('.') |> ascii_string([?0..?9], min: 1))
    |> reduce({List, :to_string, []})
    |> reduce(:to_number)

  float_parser =
    choice([
      float
      |> concat(fuzz)
      |> concat(unsigned_float)
      |> reduce(:range)
      |> unwrap_and_tag(:float_range),
      float |> unwrap_and_tag(:float)
    ])
    |> repeat(space)
    |> eos()
    |> label("a real number, like `2.7182818' or `-10'")

  defparsec(:parse, float_parser)
end