Boolean-logic evaluator in Rust

This is a basic calculator, written with @Sammy99Jsp's assistance, intended to teach me how to write code in Rust.

It includes basic functionality, such as :

• Various logical operations ("gates")
  • AND
  • OR
  • NAND
  • NOR
  • XAND
  • XOR
  • XNAND
  • XNOR
• Error handling (the program repeats the question until the user provides a satisfactory answer).
• "mem" feature (as in "memory"), which allows the user to reuse the previous output of the program.
• NOT gate, which negates the input (i.e. 'not True' -> 'False').
• "exit" feature, which safely terminates the program.