LetExp([
 FunctionDec[
  (g,[   
   (a,true,int)],
SOME(int),
   VarExp(
    SimpleVar(a))),
  (g,[   
   (a,true,string)],
SOME(int),
   IntExp(5))],
 VarDec(x,true,NONE,
  IntExp(5))],
 CallExp(g,[
  VarExp(
   SimpleVar(x))]))