Handling user-defined operators – unary operators

We saw in the previous recipe how binary operators can be handled. A language may also have some unary operator, operating on 1 operand. In this recipe, we will see how to handle unary operators.

Getting ready

The first step is to define a unary operator in the TOY language. A simple unary NOT operator (!) can serve as a good example; let's see one definition:

def unary!(v)
  if v then
    0
  else
    1;

If the value v is equal to 1, then 0 is returned. If the value is 0, 1 is returned as the output.

How to do it...

Do the following steps:

1. The first step is to define the enum token for the unary operator in the toy.cpp file:

   enum Token_Type {
   …
   …
   BINARY_TOKEN,
   UNARY_TOKEN
   }

2. Then we identify the unary string and return a unary token:

   static int get_token() {
   …
   …
   if (Identifier_string == "in") return IN_TOKEN;
   if (Identifier_string == "binary") return BINARY_TOKEN;
   if (Identifier_string =...