Method is_let_var

crates/kernel/src/tc.rs:501–511

Whether a de-Bruijn variable points at a let-bound local.

(&self, idx: u64)

  pub fn lookup_let_val(&mut self, idx: u64) -> Option<KExpr<M>> {
    let n = self.ctx.len();
    let idx_us = usize::try_from(idx).ok()?;
    if idx_us >= n {
      return None;
    }
    let level = n - 1 - idx_us;
    let val = self.let_vals[level].as_ref()?.clone();
    Some(lift(&mut self.env.intern, &val, idx + 1, 0))
  }

  /// Whether a de-Bruijn variable points at a let-bound local.
  pub fn is_let_var(&self, idx: u64) -> bool {
    let n = self.ctx.len();
    let Some(idx_us) = usize::try_from(idx).ok() else {
      return false;