LetExp([
 TypeDec[
  (intlist,
   RecordTy[
    (hd,true,int),
    (tl,true,intlist)]),
  (tree,
   RecordTy[
    (key,true,int),
    (children,true,treelist)]),
  (treelist,
   RecordTy[
    (hd,true,tree),
    (tl,true,treelist)])],
 VarDec(lis,true,SOME(intlist),
  RecordExp(intlist,[
   (hd,
    IntExp(0)),
   (tl,
    NilExp)]))],
 VarExp(
  SimpleVar(lis)))