takuma-saito/mini_erb.rb

## mini_erb.rb
require 'strscan'

BEGIN_TAGS = %w(<%= <%# <%)
END_TAGS = %w(%>)
class MiniErb
  def scan(content)
    scanner = ::StringScanner.new(content)
    state = :text
    until scanner.eos?
      case state
      when :text
        scanner.scan(/(.*?)?(#{BEGIN_TAGS.join("|")}|\z)/m)
        if scanner[2].nil?
          yield(scanner[1], state)
        else
          yield(scanner[1], state)
          state = :begin
          yield(scanner[2], state)
          state = :code
        end
      when :code
        scanner.scan(/(.*?)(#{END_TAGS.join("|")}|\z)/m)
        if scanner[2].nil?
          yield(scanner[1], state)
        else
          yield(scanner[1], state)
          state = :end
          yield(scanner[2], state)
          state = :text
        end
      end
    end
  end
  def compile(content, bind = binding)
    src =
      self
        .enum_for(:scan, content)
        .each_with_object({curr: '', text: '', tag: nil}) do |values, memo|
      token, state = values
      case state
      when :text
        memo[:text] += %Q(print "#{token.gsub('"', '\\"')}";)
      when :begin
        memo[:curr] = ''
        memo[:tag]  = token
      when :end
        add_code(token, memo)
      when :code
        memo[:curr] += token
      end
    end
    # puts src[:text]
    eval(src[:text], bind, __FILE__, __LINE__)
  end
  def add_code(token, memo)
    case memo[:tag]
    when '<%'
      memo[:text] += %Q( #{memo[:curr]}; )
    when '<%='
      memo[:text] += %Q( print #{memo[:curr]}; )
    when '<%#'
      # skip
    else
      fail
    end
    memo[:curr] = ''
  end
end

puts MiniErb.new.compile("#{<<-BEGIN}")
<html>
  <body>
    <p><%= 'hoge' %></p>
    <div class="main">
      <% ['a', 'b', 'c'].each do |val| %>
        <div class="sub"><%= val %></div>
      <% end %>
    </div>
  </body>
</html>
BEGIN
hoge = 'fuga'
puts MiniErb.new.compile("#{<<-BEGIN}", binding)
<%= 'ok' %>
<%= hoge %>
<body><% (0..10).each do |i| %><p><%= i %></p><% end %></body>
<%# comment_out %>
BEGIN
	require 'strscan'

	BEGIN_TAGS = %w(<%= <%# <%)
	END_TAGS = %w(%>)
	class MiniErb
	def scan(content)
	scanner = ::StringScanner.new(content)
	state = :text
	until scanner.eos?
	case state
	when :text
	scanner.scan(/(.*?)?(#{BEGIN_TAGS.join("\|")}\|\z)/m)
	if scanner[2].nil?
	yield(scanner[1], state)
	else
	yield(scanner[1], state)
	state = :begin
	yield(scanner[2], state)
	state = :code
	end
	when :code
	scanner.scan(/(.*?)(#{END_TAGS.join("\|")}\|\z)/m)
	if scanner[2].nil?
	yield(scanner[1], state)
	else
	yield(scanner[1], state)
	state = :end
	yield(scanner[2], state)
	state = :text
	end
	end
	end
	end
	def compile(content, bind = binding)
	src =
	self
	.enum_for(:scan, content)
	.each_with_object({curr: '', text: '', tag: nil}) do \|values, memo\|
	token, state = values
	case state
	when :text
	memo[:text] += %Q(print "#{token.gsub('"', '\\"')}";)
	when :begin
	memo[:curr] = ''
	memo[:tag] = token
	when :end
	add_code(token, memo)
	when :code
	memo[:curr] += token
	end
	end
	# puts src[:text]
	eval(src[:text], bind, __FILE__, __LINE__)
	end
	def add_code(token, memo)
	case memo[:tag]
	when '<%'
	memo[:text] += %Q( #{memo[:curr]}; )
	when '<%='
	memo[:text] += %Q( print #{memo[:curr]}; )
	when '<%#'
	# skip
	else
	fail
	end
	memo[:curr] = ''
	end
	end

	puts MiniErb.new.compile("#{<<-BEGIN}")
	<html>
	<body>
	<p><%= 'hoge' %></p>
	<div class="main">
	<% ['a', 'b', 'c'].each do \|val\| %>
	<div class="sub"><%= val %></div>
	<% end %>
	</div>
	</body>
	</html>
	BEGIN
	hoge = 'fuga'
	puts MiniErb.new.compile("#{<<-BEGIN}", binding)
	<%= 'ok' %>
	<%= hoge %>
	<body><% (0..10).each do \|i\| %><p><%= i %></p><% end %></body>
	<%# comment_out %>
	BEGIN