Improve readability of code by using if expression

[pjljvandelaar]

The code is simplified by using if expressions (and simplifying that when possible).

This pull requests solves #5

Problem detected and solved by Rejuvenation-Ada crate

[pjljvandelaar]

If this merge is accepted,
I could also check for the usage of short circuit versions of Boolean operators:

See e.g.
https://github.com/TNO/Rewriters-Ada/blob/47ca5f092d736ce7ab86a0214008023dd59b2f4f/src/predefined_rewriters_prefer_short_circuit.ads#L26-L31

[gusthoff]

Sorry for the delay: I'll take a look into your changes as soon as I have some spare time.

Feel free to perform others checks. The only thing I'd like to ask you, though, is to avoid creating an issue and a pull request at the same time: creating a pull request alone is more than sufficient.