gosukiwi

class SentenceParser < BaseParser
  def match(tokens)
    match_first tokens, emphasis_parser, bold_parser, text_parser
  end
end

gosukiwi

class BoldParser < BaseParser
  def match(tokens)
    return Node.null unless tokens.peek_or(%w(UNDERSCORE UNDERSCORE TEXT UNDERSCORE UNDERSCORE), %w(STAR STAR TEXT STAR STAR))
    Node.new(type: 'BOLD', value: tokens.third.value, consumed: 5)
  end
end

gosukiwi

class TextParser < BaseParser
  def match(tokens)
    return Node.null unless tokens.peek('TEXT')
    Node.new(type: 'TEXT', value: tokens.first.value, consumed: 1)
  end
end

gosukiwi

                +------[START]--------+
                |         |           |
                v         v           v
             [BINOP] [OPERATOR=-] [NUMBER=4]
                |
   +------------+----------+
   |            |          |
   v            v          v
[NUMBER=2] [OPERATOR=+] [NUMBER=2]

gosukiwi

   +------[START]----------+
   |          |            |
   v          v            v
[NUMBER=2] [OPERATOR=+] [BINOP]
                           |
              +------------+----------+
              |            |          |
              v            v          v
           [NUMBER=2] [OPERATOR=-] [NUMBER=4]

gosukiwi

Start    := Binop
Binop    := Binop Operator Binop
          | Number
Operator := + | - | * | /
Number   := 0 | 1 | 2 | ... | 9

gosukiwi

class BaseParser
  private

  # We use some reflection to prettify the parser depedencies. Basically, from
  # calling a `foo_parser` method is the same as doing `ParserFactory.build('foo_parser')`.
  #
  def method_missing(name, *args, &block)
    raise ArgumentError.new("Method #{name} does not exist.") unless name.to_s.end_with?('_parser')
    ParserFactory.build(name, *args, &block)
  end

gosukiwi

Start          := Binop
Binop          := Subtraction
Subtraction    := Adition "-" Binop
                | Adition
Adition        := Division "+" Binop
                | Division
Division       := Multiplication "/" Binop
                | Multiplication
Multiplication := Number "*" Binop
                | Number

gosukiwi

Body               := Paragraph*

Paragraph          := SentenceAndNewline
                    | SentenceAndEOF
                    
SentenceAndNewline := Sentence+ NEWLINE NEWLINE
SentencesAndEOF    := Sentence+ NEWLINE EOF
                    | Sentence+ EOF
                    
Sentence           := EmphasizedText

gosukiwi

class Generator
  def generate(ast)
    body_visitor.visit(ast)
  end

  private

  def body_visitor
    BodyVisitor.new
  end