forwad declaration of parser

[dashbitco]

forwad declaration of parser

[josevalim]

I just noticed the docs for it aren’t good :( see the examples/simple_xml or tests. I will push better examples later. :) -- *José Valimwww.plataformatec.com.br <http://www.plataformatec.com.br/>Founder and Director of R&D*

[josevalim]

For recursion, you need to new intermediate parsers with defparsec and use the parsec combinator to invoke them. -- *José Valimwww.plataformatec.com.br <http://www.plataformatec.com.br/>Founder and Director of R&D*

[meox]

could you explain it with a very simple exaple?
thanks a lot

[josevalim]

Not at the computer right now. Please see the docs for a function named parsec or the tests. -- *José Valimwww.plataformatec.com.br <http://www.plataformatec.com.br/>Founder and Director of R&D*

[josevalim]

I have pushed a smaller simple_xml example to the parsec docs: https://hexdocs.pm/nimble_parsec/NimbleParsec.html#parsec/2

[meox]

Thanks!
I tested it with this:

defmodule Expr do
  import NimbleParsec

  #
  # expr   := term + expr | term
  # term   := factor * term | factor
  # factor := ( expr ) | nat
  # nat    := 0 | 1 | 2 | ...
  #

  nat = integer(min: 1) |> unwrap_and_tag(:nat)

  defparsec :expr,
    choice([
      parsec(:term)
      |> ignore(ascii_char([?+]))
      |> concat(parsec(:expr))
      |> tag(:plus),
      parsec(:term)
    ])

  defparsecp :term,
    choice([
      parsec(:factor)
      |> ignore(ascii_char([?*]))
      |> concat(parsec(:term))
      |> tag(:mul),
      parsec(:factor)
    ])

  defparsecp :factor,
    choice([
      ignore(ascii_char([?(]))
      |> concat(parsec(:expr))
      |> wrap()
      |> ignore(ascii_char([?)])),
      nat
    ])

end