expr_fvs (Lam bndr body) fv_cand in_scope acc =
  addBndr bndr (expr_fvs body) fv_cand in_scope acc
expr_fvs (Lam bndr body) fv_cand in_scope acc =
  addBndr bndr (expr_fvs body) fv_cand in_scope acc
expr_fvs (Lam bndr body) fv_cand in_scope acc =
  addBndr bndr (expr_fvs body) fv_cand in_scope acc