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