Minor refactoring

[jaraco]

While exploring the code, I found a few places where I thought these changes might make the code more direct and concise.

• Replace for/if/else with single or expression.
• Use expression algebra to calculate a 'file_target'
• Handle normal condition in the body.
• Use expression algebra to calculate dependencies.

Feel free to cherrypick the ones you like or reject wholesale.

[pfmoore]

Thanks for the suggestions. I won't actually apply them as personally I find the altered code harder to reason about and understand. Specifically, I find the idiom of "multiply by a bool" to be unintuitive, and I'm not a fan of expressions being used for side effects simply to avoid an if statement. There's nothing wrong with the ideas, but they feel like they are more rooted in a functional way of thinking, rather than using simpler (but more verbose) procedural idioms.

I appreciate the time you spent making a PR with your suggestions, though.