LetExp([
 TypeDec[
  (rectype,
   RecordTy[
    (name,true,string),
    (age,true,int)])],
 VarDec(rec1,true,SOME(rectype),
  RecordExp(rectype,[
   (name,
    StringExp("Nobody")),
   (age,
    IntExp(1000))]))],
 SeqExp[
  AssignExp(
   FieldVar(
    SimpleVar(rec1),
    name),
   StringExp("Somebody")),
  VarExp(
   SimpleVar(rec1))])