How can I feed a top-level CUE value into an expression during export?

[cueckoo]

Originally opened by @seh in cuelang/cue#1054

Suppose I have CUE file with the following content:

[
	{
		a: 1
	},
	{
		b: 2
	},
]

It's a top-level list, not a struct with any field names.

Suppose I'd like to export it as a multi-document YAML stream. Ideally I'd be able to refer to this top-level value in a command like this:

cue export list.cue --out=text --expression='yaml.MarshalStream($)'

Here I used the identifier $ in an appeal to Jsonnet, as some way to refer to the top-level value, but of course $ is not understood by CUE.

I experimented with using the --path and --with-context flags, to no avail.

[myitcv]

@seh - thanks for your patience whilst we complete the migration (#1078)

Per our offline conversation, I'm not aware of a way of achieving this. Indeed in #564 (comment) @mpvl and I discussed the possibility of using a bare . to refer to the current scope.

So in this case that would look like:

cue export list.cue --out=text --expression='yaml.MarshalStream(.)'

How does that sit with you?

[seh]

That sounds like a good choice, assuming that there's no syntactic ambiguity there. There's plenty of precedent in other "path selection" languages.

[myitcv]

Great. I've marked this for discussion with @mpvl. I'll create a new issue if it turns out we don't repurpose #564.