What's the purpose of the Word AST type?

[hwittenborn]

Looking at the Word AST type, it appears to just be a wrapper around a String with no extra functionality. I see that there's a Word::flatten method, but this just returns the string itself.

Am I overlooking something?

[reubeno]

Good question. It exists to leverage the type system in distinguishing raw strings (that are not words-requiring expansion) from formal words in the grammar that require full expansion in accordance with the spec.

This forces users of the type to make an explicit decision as to whether they want to convert it to a string or expand it via basic or full expansion.

[reubeno]

I'd also add that it also provides an attachment point for future extension. If we are able to propagate source information through later, having the struct gives us somewhere to place it without needing to track down all of the loose Strings that would need to be enlightened.

[hwittenborn]

I agree with that, I did picture the Word type including source information and the like.

[hwittenborn]

Good question. It exists to leverage the type system in distinguishing raw strings (that are not words-requiring expansion) from formal words in the grammar that require full expansion in accordance with the spec.

Could you elaborate on what you mean by that? The way I understood, you're trying to say that the Word type is for use with things like variable expansion, though such also appears to take strings as inputs.

[reubeno]

The AST is designed to be intentional at when its nodes embed Strings versus when it embeds Words. They are physically the same, but the latter are generally required to go through "word expansion" (see section 2.6 of the spec).

There may be discrepancies in the code base. If they're intentional, ideally there would be a reason and sufficient commenting. And if not, then it may very well be a bug / oversight. Please do report any such issues!

[hwittenborn]

Got it, that makes more sense! So, for example, the value of an assignment operation should always be a Word, and it's required to undergo "word expansion" before I can see how it's supposed to properly look (i.e. variable expansion, brace expansion, etc)?

[reubeno]

You got it 🙂

If you look at the admittedly giant interp.rs you'll see how we do this in our core shell interpreter.