Let statement on compiler repl gives out a value and not null

[Yag000]

Description

When using the compiler on the REPL, I get a value different from null when assigning variables with a let statement."

Steps to reproduce

cargo run

and simply type

let a = 4;

Expected behavior

Welcome to the Monkey programming language! Compiler and Interpreter by @Yag000, in Rust
Feel free to type in commands

>> let a = 4;

Actual behavior

Welcome to the Monkey programming language! Compiler and Interpreter by @Yag000, in Rust
Feel free to type in commands

>> let a = 4;
4

Additional information

This only happens when using the compiler as an engine. This is due to the fact that 4 is at the top of the stack, which is not an intended behavior in this case. NULL should be there. I will look at this later as it does not have any practical implications, and it will not mess with anyone, but it should be addressed.

[Yag000]

I would argue that this is just a feature of the compiler, since when using the REPL you just get the top constant, which in most cases is, ans should be, a value different from 'NULL'. To solve this I would hard code on the REPL itself that it should only print a value if the last input was an expression statement, and ignore the top value in any other case.