gosukiwi

class TextScanner < SimpleScanner
  def self.from_string(plain_markdown)
    text = plain_markdown
           .each_char
           .take_while { |char| SimpleScanner.from_string(char).null? }
           .join('')
    Token.new(type: 'TEXT', value: text)
  rescue InvalidTokenError
    Token.null
  end

gosukiwi

class SimpleScanner
  TOKEN_TYPES = {
    '_'  => 'UNDERSCORE',
    '*'  => 'STAR',
    "\n" => 'NEWLINE'
  }.freeze

  def self.from_string(plain_markdown)
    char = plain_markdown[0]
    Token.new(type: TOKEN_TYPES[char], value: char)

gosukiwi

A paragraph __with__ some *text*

gosukiwi

class Token
  attr_reader :type, :value
  def initialize(type:, value:)
    @type = type
    @value = value
    raise InvalidTokenError if value.nil? || type.nil?
  end

  def self.null
    NullToken.new

gosukiwi

foo = 1

gosukiwi

foo = bar # expects a number on the right hand side of the equation
foo       # no equals, no number
foo =     # nothing here!
= foo     # nothing on the left hand side

gosukiwi

RuleName := SomeOtherRule A_TERMINAL

gosukiwi

Start := a
       | b
       | c

gosukiwi

A := a*

gosukiwi

B := b+