invert.sweet.js

macro invert {
  rule { { $x:ident <- $y:expr } } => {
    $y(function($x) { return $x })
  }
  rule { { $x:ident <- $y:expr $rest ... } } => {
    $y(function($x) {
      return invert { $rest ... }
    })
  }
  rule { { $y:expr } } => { $y }
}

invert {
  y <- x.flatMap
  z <- y.flatMap
  z + 1
}

invert2.sweet.js

macro invert {
  rule { { $ys ... | $x:ident -> $rest ... } } => {
    ($ys ...)(function($x) {
      return invert { $rest ... }
    })
  }
  rule { { $ys ... } } => {
    $ys ...
  }
}

invert {
  x.onNext | next ->
  next.flatMap | y ->
  y+1
}