Open the toy.cpp file as follows:

$ vi toy.cpp

The function to generate code for numeric values can be defined as follows:

Value *NumericAST::Codegen() {
  return ConstantInt::get(Type::getInt32Ty(getGlobalContext()), numeric_val);
}

In LLVM IR, integer constants are represented by the ConstantInt class whose numeric value is held by the APInt class.

The function for generating code for variable expressions can be defined as follows:

Value *VariableAST::Codegen() {
  Value *V = Named_Values[Var_Name];
  return V ? V : 0;
}

The Codegen() function for binary expression can be defined as follows:

Value *BinaryAST::Codegen() {
  Value *L = LHS->Codegen();
  Value *R = RHS->Codegen();
  if(L == 0 || R == 0) return 0;
  
  switch(atoi(Bin_Operator.c_str...