gistfile1.nim

type
  PNode = ref TNode
  TNode = object
    variant
    of nkInt: val: int
    of nkFloat: val: float
    of nkString: val: string
    of nkAdd, nkSub:
      leftOp, rightOp: PNode
    of nkIf:
      condition, thenPart, elsePart: PNode

# create a new case object:
var n = nkIf(condition: nil)
# accessing n.thenPart is valid because the ``nkIf`` branch is active:
n.thenPart = nkFloat(val: 2.0)


var x = PNode(nkAdd(leftOp: PNode(nkInt(val: 4)),
                           rightOp: PNode(nkInt(val: 2))