proposal / as namespace path separator and . for current namespace

[ceedubs]

Something that comes up repeatedly is that it's awkward that in ucm there isn't a way to reference the current namespace (without fully typing it out). It would be nice to be able to do something like fork . .pr.thing where the first . is a hypothetical "current namespace" reference and .pr.thing is a namespace outside of the current namespace.

Many Unison developers will likely be familiar with Unix-style paths, where . refers to the current directory, and .. refers to the parent directory. The familiarity makes . and .. promising candidates for ucm "current namespace" and "parent namespace" references. However, in Unison . is used as the path separator for namespaces (ex: lib.base), which clashes with using . to reference the current namespace.

Because of the ubiquitous nature of Unix conventions and ucm already embracing some of them (ex: ls, cd), I propose adopting / as the path separator and . as the current namespace. This would be a pretty big change that would require updating lots of documentation and possibly messing with URIs (such as on Share). However, it seems to kind of be what people expect, and there isn't an obvious way to add a "current namespace" reference without going down this route.

Unfortunately / is also a common operator name (ex: division, appending to a path), so we'd have to figure out how to still allow it as an operator name, which likely means escaping it with backticks or parens or something.

[pchiusano]

We use / as the separator between a project and its branch, so unless we use a different separator there, or somehow introduce some leading character for project references (which I don't care for), using / as the path separator seems like a problem.

I'd almost be inclined to get rid of .. and . entirely and just have special keyword-y paths like :here and :root or something. Another option is to keep .. but introduce :root or @root, and then change . to mean "current path".

I'd also like to see the situations where it's awkward, since we are getting dedicated commands for common use cases, so maybe that will help too.

Like to create a branch off of main, you do project/main> branch.fork myfeature to make a branch forked off main, you don't need to do fork @here /myfeature (though we could support this too).

[timjs]

I really like the idea of using / as a path separator. The backslash as a path separator is so ubiquitous, that ucm actually already uses it: when using ls, namespaces are printed with a trailing /.

Also, I think it will allow us to use . for record field access in #3845. Which would be beneficial, as . is used this way in a lot of programming languages. It lowers the bar for easy adoption of Unison.

For prior art: see Koka. It uses / as a module separator and . for field access (which are actually function calls).