Method intern

crates/kernel/src/tc.rs:970–972

Intern an expression through the mutable intern environment.

(&mut self, e: KExpr<M>)

    f: impl FnOnce(&mut Self) -> R,
  ) -> R {
    let saved = self.lctx.len();
    let result = f(self);
    self.lctx.truncate(saved);
    result
  }