questions about do unchained supplemental code

Stream: general

[Frederick Pu]

In the do unchained supplemental code for for loops https://github.com/Kha/do-supplement/blob/master/Do/For.lean
I'm having diffuculty understanding how the runCatch is able to differentiate between throws from continue and throw from break. Since both throw unit. If the for loop body has body has both continue and break inside of it since both throw (). Also how does it distinguish between throws from return and throws from break?

[Frederick Pu]

macro_rules
  | `(d! for $x in $e do' $s) => do  -- (D5), optimized like (1')
    let mut s := s
    let sb ← expandStmt (← `(stmt| expand! break in $s))
    let hasBreak := sb.raw.count (· matches `(stmt| break)) < s.raw.count (· matches `(stmt| break))
    if hasBreak then
      s := sb
    let sc ← expandStmt (← `(stmt| expand! continue in $s))
    let hasContinue := sc.raw.count (· matches `(stmt| continue)) < s.raw.count (· matches `(stmt| continue))
    if hasContinue then
      s := sc
    let mut body ← `(d! $s)
    if hasContinue then
      body ← `(ExceptCpsT.runCatch $body)
    let mut loop ← `(forM $e (fun $x => $body))
    if hasBreak then
      loop ← `(ExceptCpsT.runCatch $loop)
    pure loop
  | `(d! break%$b) =>
    throw <| Macro.Exception.error b "unexpected 'break' outside loop"
  | `(d! continue%$c) =>
    throw <| Macro.Exception.error c "unexpected 'continue' outside loop"

[Frederick Pu]

nvm i get it now, since the expand calls for lift, the things in the inner most scope will always have escape priority. Since return gets expanded before break which gets expanded conitnue etc