pub const SCHEME_BASE: u32 = 1_000_000;Expand description
The base a declaration’s type parameters are numbered from.
The nth parameter of a declaration is Ty::Var(SCHEME_BASE + n) wherever it appears in that
declaration’s field types, so instantiating Tree[Str] is an index rather than a search. The
base is far above any unification variable the checker will mint, which is what lets one Ty
carry both without a tag.