From 40bf75cbff89135489b8489ef694c2abd7006cf2 Mon Sep 17 00:00:00 2001
From: Gabriel Ebner <gebner@gebner.org>
Date: Sun, 7 May 2017 15:52:39 +0200
Subject: [PATCH] fix(library/equations_compiler/structural_rec): fix indices

---
 .../equations_compiler/structural_rec.cpp     |  9 ++--
 tests/lean/run/lamexp.lean                    | 46 +++++++++++++++++++
 2 files changed, 50 insertions(+), 5 deletions(-)
 create mode 100644 tests/lean/run/lamexp.lean

diff --git a/src/library/equations_compiler/structural_rec.cpp b/src/library/equations_compiler/structural_rec.cpp
index a607b9996d..bc2bd9c7e0 100644
--- a/src/library/equations_compiler/structural_rec.cpp
+++ b/src/library/equations_compiler/structural_rec.cpp
@@ -339,24 +339,23 @@ struct structural_rec_fn {
         expr fn_type   = ctx.infer(fn);
         unsigned arity = ues.get_arity_of(0);
         expr rec_arg;
+        buffer<expr> args;
         buffer<expr> other_args;
-        buffer<expr> pre_idx_args;
         for (unsigned i = 0; i < arity; i++) {
             fn_type = ctx.whnf(fn_type);
             if (!is_pi(fn_type)) throw_ill_formed_eqns();
             expr arg = locals.push_local_from_binding(fn_type);
+            args.push_back(arg);
             if (i == m_arg_pos) {
                 rec_arg = arg;
-            } else if (std::find(m_indices_pos.begin(), m_indices_pos.end(), i) != m_indices_pos.end()) {
-                pre_idx_args.push_back(arg);
-            } else {
+            } else if (std::find(m_indices_pos.begin(), m_indices_pos.end(), i) == m_indices_pos.end()) {
                 other_args.push_back(arg);
             }
             fn_type  = instantiate(binding_body(fn_type), arg);
         }
         buffer<expr> idx_args;
         for (unsigned i : m_indices_pos)
-            idx_args.push_back(pre_idx_args[i]);
+            idx_args.push_back(args[i]);
         buffer<expr> I_params;
         expr I = get_app_args(ctx.relaxed_whnf(ctx.infer(rec_arg)), I_params);
         unsigned nindices = m_indices_pos.size();
diff --git a/tests/lean/run/lamexp.lean b/tests/lean/run/lamexp.lean
new file mode 100644
index 0000000000..69a4587f58
--- /dev/null
+++ b/tests/lean/run/lamexp.lean
@@ -0,0 +1,46 @@
+inductive ty
+| base : string → ty
+| arr : ty → ty → ty
+
+namespace ty
+instance : decidable_eq ty := by tactic.mk_dec_eq_instance
+instance : inhabited ty := ⟨ty.base "o"⟩
+end ty
+
+@[reducible] def ctx := list ty
+
+inductive lamexp_core : ctx → ty → Type
+| var : Π {Γ : ctx} {t} (n : ℕ), list.nth Γ n = some t → lamexp_core Γ t
+| fv : Π {Γ}, string → Π t : ty, lamexp_core Γ t
+| con : Π {Γ}, string → Π t : ty, lamexp_core Γ t
+| app : Π {Γ} {t s}, lamexp_core Γ (ty.arr t s) → lamexp_core Γ t → lamexp_core Γ s
+| abs : Π {Γ : ctx} {t s}, lamexp_core (t::Γ) s → lamexp_core Γ (ty.arr t s)
+
+namespace lamexp_core
+-- instance {Γ t} : decidable_eq (lamexp_core Γ t) := by tactic.mk_dec_eq_instance
+instance {Γ t} : inhabited (lamexp_core Γ t) := ⟨lamexp_core.con "c" t⟩
+end lamexp_core
+
+@[reducible] def lamexp := lamexp_core []
+
+namespace lamexp
+
+lemma nth_append {α} {ys : list α} : Π {n xs}, list.nth xs n ≠ none → list.nth (xs ++ ys) n = list.nth xs n
+| 0     []      h := by contradiction
+| (n+1) []      h := by contradiction
+| 0     (x::xs) h := rfl
+| (n+1) (x::xs) h := @nth_append n xs h
+
+def weaken_core : ∀ {Γ Δ t}, lamexp_core Γ t → lamexp_core (Γ ++ Δ) t
+| Γ Δ .(t) (@lamexp_core.var .(Γ) t n h) := lamexp_core.var n $
+    begin rw nth_append, assumption, rw h, intro, contradiction end
+| Γ Δ .(t) (lamexp_core.fv n t) := lamexp_core.fv n t
+| Γ Δ .(t) (lamexp_core.con n t) := lamexp_core.con n t
+| Γ Δ .(s) (@lamexp_core.app .(Γ) t s a b) := lamexp_core.app (weaken_core a) (weaken_core b)
+| Γ Δ (ty.arr .(t) .(s)) (@lamexp_core.abs .(Γ) t s a) :=
+  lamexp_core.abs $ cast (by simp) (weaken_core a)
+
+def weaken {Γ t} : lamexp t → lamexp_core Γ t :=
+weaken_core
+
+end lamexp