Function lift_program_bindings 

pub fn lift_program_bindings<'a>(
    stmts: &[Stmt<'a>],
    registry: &TypeRegistry,
    interner: &mut Interner,
    arenas: Arenas<'a>,
) -> Result<Option<Lifted<'a>>, String>

Lift the program bindings that functions reach into one lent record (see the module docs). Ok(None) when no function reaches one: the program needs nothing. Err names what this tier cannot express, in the author’s terms.