powershellでパーサコンビネータ ref: https://qiita.com/jca02266/items/b7e1dc21d8d537827290

file0.txt

  $x = $target[0..(0+4-1)]
  $y = $target[4..(4+3-1)]

file1.txt

  & seq (setvar x (tokenN 4)) `
        (setvar y (tokenN 3)) `
        $target 0

file2.txt

  $target |
    setvar x (tokenN 4) |
    setvar y (tokenN 3)

file3.txt

function token {
  Param($str)

  $len = $str.Length

  return {
    Param($target, $position)

    if ($target.Length -ge ($position + $len) -and $target.Substring($position, $len) -eq $str) {
      return @($true, $str, ($position + $len))
    } else {
      return @($false, "", $position)
    }
  }.GetNewClosure()
}

# & (token 'foobar') 'foobar' 0 # => (True, 'foobar', 6)
# & (token 'foobar') 'foobar' 1 # => (False, '', 1)

function many {
  Param($parser)

  return {
    Param($target, $position)
    $result = [Collections.ArrayList]@()

    for (;;) { 
      $parsed = & $parser $target $position

      if ($parsed[0]) {
        $result.Add($parsed[1]) | Out-Null
        $position = $parsed[2]
      } else {
        break
      }
    }

    return ($True, (-join $result), $position)
  }.GetNewClosure()
}

# & (many (token 'hoge')) 'hogehoge' 0 # => (True, ('hoge', 'hoge'), 8)
# & (many (token 'hoge')) '' 0   # => (True, '', 0)

function choice {
  $parsers = $args

  return {
    Param($target, $position)

    for ($i = 0; $i -lt $parsers.Length; $i++) {
      $parsed = & $parsers[$i] $target $position
      if ($parsed[0]) {
        return $parsed
      }
    }

    return ($false, '', $position)
  }.GetNewClosure()
}


# $parse = many (choice (token 'hoge') (token 'fuga'))
#
# & $parse '' 0           # => (True, '', 0)
# & $parse 'hogehoge' 0   # => (True, ('hoge', 'hoge'), 8)
# & $parse 'fugahoge' 0   # => (True, ('fuga', 'hoge'), 8)
# & $parse 'fugafoo' 0    # => (True, 'fuga', 4)

function seq {
  $parsers = $args

  return {
    Param($target, $position)

    $result = [Collections.ArrayList]@()
    for ($i = 0; $i -lt $parsers.Length; $i++) {
      $parsed = & $parsers[$i] $target $position

      if ($parsed[0]) {
        $result.Add($parsed[1]) | Out-Null
        $position = $parsed[2]
      } else {
        return @($false, '', $position)
      }
    }
    return @($true, (-join $result), $position)
  }.GetNewClosure()
}

# $parse = seq (token 'foo') (choice (token 'bar') (token 'baz'))
#
# & $parse 'foobar' 0  # => (True, ('foo', 'bar'), 6)
# & $parse 'foobaz' 0  # => (True, ('foo', 'baz'), 6)
# & $parse 'foo' 0     # => (False, '', 3)

function option {
  Param($parser)

  return {
    Param($target, $position)

    $result = & $parser $target $position

    if ($result[0]) {
      return $result;
    } else {
      return ($true, '', $position)
    }
  }.GetNewClosure()
}

# $parser = option (token 'hoge')
#
# & $parser 'hoge' 0 # => (True, 'hoge', 4)
# & $parser 'fuga' 0 # => (True, '', 0)

function regex {
  Param($regexp)

  if ($regexp -is [String]) {
    $regexp = New-Object Regex ($regexp)
  }

  if (! $regexp.ToString().StartsWith("\G")) {
    $regexp = New-Object Regex (("\G" + $regexp.ToString()), $regexp.Options)
  }

  return {
    Param($target, $position)

    $regexResult = $regexp.Match($target, $position)

    if ($regexResult.Success) {
      $position += $regexResult.Length;
      return ($true, $regexResult.Value, $position)
    } else {
      return ($false, "", $position)
    }
  }.GetNewClosure()
}

# $parser = regex "hoge"
#
# & $parser 'hoge' 0 # => [true, 'hoge', 4]を返す

# $parser = regex ([regex]"([1-9][0-9]*)")
#
# & $parser '2014' 0 # => (True, '2014', 4)
# & $parser '01' 0   # => (False, '', 0)

file4.txt

& {
  $foo = "FOO"

  $bar = {
    Write-Warning $foo
  }.GetNewClosure()

  $foo = "BAR"

  & $bar
}