[BUG]: Conditional expression results in a bool type (inconsistent with python)

[davidbrownell]

Bug description

The following code in Mojo prints True:

fn main():
    let x = 0
    print(x or "hello")

In python, the following code prints hello:

print(0 or "hello")

Steps to reproduce

• Build the provided code in mojo and python to see the differences in behavior.

System information

- What OS did you install Mojo on? 
Ubuntu 22.04

- Provide version information for Mojo by pasting the output of `mojo -v`?
mojo 0.7.0 (af002202)

- Provide Modular CLI version by pasting the output of `modular -v`
modular 0.4.1 (2d8afe15)

[laszlokindrat]

We discussed the unexpected behavior of short circuiting conditional expressions in Mojo, such as the expression 0 or "hello" evaluating to a True value (of Bool type). Since Mojo is a statically typed language, it is not trivial to mimic Python’s behavior in this case, since the type of these expressions are not always obvious. In the future, we might be able to do something using existentials: the compiler could find the common traits (or methods) on the types of the two operands and emit something with that conforms to those. For now, we decided that we will not change the existing behavior until we have more dynamic features built out. However, we will document this behavior since it is a potentially confusing deviation from Python.

[davidbrownell]

Thank you for the information, Laszlo!