Don't use String

[phadej]

We use String for names, not great.

I think ShortText is better. I don't think there can be identifiers which are not valid text. But we can also use ShortByteString to be sure.

That said, I think having a newtype Name would help separate names from everything else. (In particular Names is something we will need to mangle as lexically C and Haskell are different)

[edsko]

Putting some basic infra in place for this, but will defer name mangling to a separate ticket #189.