Gate Expression Parser

Inspired by this expression in the CPIT201 book, I decided to write code to parse the expression and obtain the result. Somehow, the code I wrote to parse the expression ended up becoming a very simple language.

Note

There is a small bug with how NOT works, instead of flipping the given bits, it flips all bits (Bits are stored as a number, not a string). To avoid the bug, use 1111 XOR 1100 instead of NOT 1100

Example 1

Example 2

Process to parse each line

For example, with this line of code

result1 = (input1 AND (NOT input2)) OR ((NOT input1) AND input2)

It will go through this process:

• Convert each part into a 'Token'

['result1', '=', '(', 'input1', 'AND', '(', 'NOT', 'input2', ')', ')', 'OR', '(', '(', 'NOT', 'input1', ')', 'AND', 'input2', ')']

• Convert the expression into Reverse Polish Notation (also known as Postfix)

['result1', 'input1', 'input2', 'NOT', 'AND', 'input1', 'NOT', 'input2', 'AND', 'OR', '=']

• Then, the Postfix expression will be parsed as such:
  • Operands are pushed onto the Stack
  • Operators pop the needed operators from the stack
  • The result is pushed back onto the stack
  • Repeat until the expression is finished

References

• Reverse Polish Notation Video
• Reverse Polish Notation Algorithm Implementation