DSL で IF文

dsl.rb

require 'pp'
$dsl = []
$if_stack = []
def IF(cond=Proc.new)
  $if_stack << []
  $if_stack.last << {}
  $if_stack.last.last[:cond] = cond
end
def THEN(expr=Proc.new)
  $if_stack.last.last[:expr] = expr
end
def ELSIF(cond=Proc.new)
  $if_stack.last << {}
  $if_stack.last.last[:cond] = cond
end
def ELSE(expr=Proc.new)
  $if_stack.last << {}
  $if_stack.last.last[:cond] = -> { true }
  $if_stack.last.last[:expr] = expr
end
def ENDIF
  $dsl << {if: $if_stack.pop}
end
def Object.const_missing(name)
  send(name)
end
def do_inst(inst)
  symbol, stmt = *inst.keys, *inst.values
  case symbol
  when :if
    do_if(stmt)
  end
end

def do_if(if_stmt)
  if_stmt.any? {|stmt|
    if stmt[:cond].()
      stmt[:expr].()
      true
    else
      false
    end
  }
end

dice = rand(6) + 1
IF { dice == 6 }
THEN {
  puts "#{dice}!"
}
ELSIF { dice == 1 }
THEN {
  puts "#{dice}..."
}
ELSE {
  puts 'else'
  dice = rand(6) + 1
  IF { dice == 6 }
  THEN {
    puts "#{dice}!"
  }
  ELSIF { dice == 1 }
  THEN {
    puts "#{dice}..."
  }
  ELSE {
    puts 'else'
    dice = rand(6) + 1
    IF { dice == 6 }
    THEN {
      puts "#{dice}!"
    }
    ELSIF { dice == 1 }
    THEN {
      puts "#{dice}..."
    }
    ELSE {
      puts dice
    }
    ENDIF
  }
  ENDIF
}
ENDIF

pp $dsl
$dsl.each(&method(:do_inst))