Snippet from https://play.nim-lang.org

playground.nim

import macros,options

type C = ref object
  c: int

macro until(cond,node,body:untyped):untyped =
  # Example implementation, just to prove it's possible
  # Generates:
  # for raw in b:
  #   if cond(raw): break
  #   when declared Option:
  #     when raw is Option:
  #       let a = raw.get
  #     else:
  #       let a = raw
  #   else:
  #     let a = raw
  #   body
  # 
  let 
    el = node[1]
    list = node[2]
    rawel = newIdentNode("rawel")
  var
    brk = newNimNode(nnkBreakStmt)
    cnd = newIfStmt((newCall(cond, rawel), brk))
    wnstmt = newTree(nnkWhenStmt,
      newNimNode(nnkElifBranch).add(
        newCall("declared", newIdentNode("Option")),
        newTree(nnkWhenStmt,
          newNimNode(nnkElifBranch).add(
            newCall("is",rawel, newIdentNode("Option")),
            newLetStmt(el, newCall("get", rawel))
          ),
          newNimNode(nnkElse).add(newLetStmt(el, rawel))
        ),
      ),
      newNimNode(nnkElse).add(newLetStmt(el, rawel))
    )
  brk.add(newEmptyNode())
  result = newTree( nnkForStmt,
    rawel,
    list,
    newStmtList(cnd, wnstmt, body)
  )

var b = @[C(c: 0), nil, C(c: 2)] 


until isnil, a in b:
 echo a.c
# 0

var c = @[some(2), none(int), some(8), some(10)] 

until isNone, a in c:
  echo a
# 2