LetExp([
 FunctionDec[
  (do_nothing1,[
   (a,false,int),
   (b,false,string)],
   SOME(int),
   SeqExp[
    CallExp(do_nothing2,[
     OpExp(PlusOp,
      VarExp(
       SimpleVar(a)),
      IntExp(1))]),
    IntExp(0)])],
 VarDec(d,false,NONE,
  IntExp(0)),
 FunctionDec[
  (do_nothing2,[
   (d,false,int)],
   SOME(string),
   SeqExp[
    CallExp(do_nothing1,[
     VarExp(
      SimpleVar(d)),
     StringExp("str")]),
    StringExp(" ")])]],
 CallExp(do_nothing1,[
  IntExp(0),
  StringExp("str2")]))