An emulation of do notation that remains valid javascript

do-notation-safe.sjs

macro DO {
  rule { ($name:ident <- $expr:expr, ret($any...)) } => { ($expr).map($name => ($any...)) }
  rule { ($name:ident <- $expr:expr, $any...) } => { ($expr).chain($name => DO($any...))}
  rule { ($expr:expr, ret($any...)) } => { ($expr).map(() => ($any...)) }
  rule { ($expr:expr, $any...) } => { ($expr).chain(() => DO($any...)) }
  rule { ($expr:expr) } => { ($expr) }
}

export DO;

test-do-expanded.js

function render$656() {
    return fetchA().chain(resA$660 => fetchB().chain(resB$661 => fetchC().map(resC$662 => Element({
        A: resA$660,
        B: resB$661,
        C: resC$662
    }))));
}

test-do.js

function render() {
  return DO(
    resA <- fetchA(),
    resB <- fetchB(),
    resC <- fetchC(),
    ret(Element({
      A: resA,
      B: resB,
      C: resC
    }))
  );
}