diff options
Diffstat (limited to 'backends/lean')
| -rw-r--r-- | backends/lean/Base/Diverge.lean | 119 |
1 files changed, 95 insertions, 24 deletions
diff --git a/backends/lean/Base/Diverge.lean b/backends/lean/Base/Diverge.lean index 759773c9..2c764c5e 100644 --- a/backends/lean/Base/Diverge.lean +++ b/backends/lean/Base/Diverge.lean @@ -74,7 +74,7 @@ namespace Fix open Primitives open Result -variable {a b : Type} +variable {a b c d : Type} /- TODO: @@ -292,6 +292,7 @@ theorem fix_fixed_eq_terminates (f : (a → Result b) → a → Result b) (Hmono split <;> simp [*] <;> intros <;> simp [*] -- The final fixed point equation +-- TODO: remove the `forall x` theorem fix_fixed_eq {{f : (a → Result b) → a → Result b}} (Hvalid : is_valid f) : ∀ x, fix f x = f (fix f) x := by intros x @@ -313,26 +314,26 @@ theorem fix_fixed_eq {{f : (a → Result b) → a → Result b}} (Hvalid : is_va /- Making the proofs more systematic -/ -- TODO: rewrite is_mono in terms of is_mono_p - def is_mono_p (body : (a → Result b) → Result b) : Prop := + def is_mono_p (body : (a → Result b) → Result c) : Prop := ∀ {{g h}}, marrow_rel g h → result_rel (body g) (body h) - @[simp] theorem is_mono_p_same (x : Result b) : - @is_mono_p a b (λ _ => x) := by + @[simp] theorem is_mono_p_same (x : Result c) : + @is_mono_p a b c (λ _ => x) := by simp [is_mono_p, marrow_rel, result_rel] split <;> simp -- TODO: remove @[simp] theorem is_mono_p_tail_rec (x : a) : - @is_mono_p a b (λ f => f x) := by + @is_mono_p a b b (λ f => f x) := by simp_all [is_mono_p, marrow_rel, result_rel] -- TODO: rewrite is_cont in terms of is_cont_p def is_cont_p (f : (a → Result b) → a → Result b) - (body : (a → Result b) → Result b) : Prop := + (body : (a → Result b) → Result c) : Prop := (Hc : ∀ n, body (fix_fuel n f) = .div) → body (fix f) = .div - @[simp] theorem is_cont_p_same (f : (a → Result b) → a → Result b) (x : Result b) : + @[simp] theorem is_cont_p_same (f : (a → Result b) → a → Result b) (x : Result c) : is_cont_p f (λ _ => x) := by simp [is_cont_p] @@ -343,8 +344,8 @@ theorem fix_fixed_eq {{f : (a → Result b) → a → Result b}} (Hvalid : is_va -- Lean is good at unification: we can write a very general version theorem is_mono_p_bind - (g : (a → Result b) → Result b) - (h : b → (a → Result b) → Result b) : + (g : (a → Result b) → Result c) + (h : c → (a → Result b) → Result d) : is_mono_p g → (∀ y, is_mono_p (h y)) → is_mono_p (λ f => do let y ← g f; h y f) := by @@ -364,8 +365,8 @@ theorem fix_fixed_eq {{f : (a → Result b) → a → Result b}} (Hvalid : is_va theorem is_cont_p_bind (f : (a → Result b) → a → Result b) (Hfmono : is_mono f) - (g : (a → Result b) → Result b) - (h : b → (a → Result b) → Result b) : + (g : (a → Result b) → Result c) + (h : c → (a → Result b) → Result d) : is_mono_p g → is_cont_p f g → (∀ y, is_mono_p (h y)) → @@ -417,12 +418,12 @@ theorem fix_fixed_eq {{f : (a → Result b) → a → Result b}} (Hvalid : is_va apply Hhcont; assumption -- TODO: move - def is_valid_p (f : (a → Result b) → a → Result b) - (body : (a → Result b) → Result b) : Prop := + def is_valid_p (k : (a → Result b) → a → Result b) + (body : (a → Result b) → Result c) : Prop := is_mono_p body ∧ - (is_mono f → is_cont_p f body) + (is_mono k → is_cont_p k body) - @[simp] theorem is_valid_p_same (f : (a → Result b) → a → Result b) (x : Result b) : + @[simp] theorem is_valid_p_same (f : (a → Result b) → a → Result b) (x : Result c) : is_valid_p f (λ _ => x) := by simp [is_valid_p] @@ -435,8 +436,8 @@ theorem fix_fixed_eq {{f : (a → Result b) → a → Result b}} (Hvalid : is_va -- apply the lemma) theorem is_valid_p_bind {{f : (a → Result b) → a → Result b}} - {{g : (a → Result b) → Result b}} - {{h : b → (a → Result b) → Result b}} + {{g : (a → Result b) → Result c}} + {{h : c → (a → Result b) → Result d}} (Hgvalid : is_valid_p f g) (Hhvalid : ∀ y, is_valid_p f (h y)) : is_valid_p f (λ f => do let y ← g f; h y f) := by @@ -473,10 +474,12 @@ theorem fix_fixed_eq {{f : (a → Result b) → a → Result b}} (Hvalid : is_va simp [*] apply is_valid.intro Hmono Hcont + -- TODO: functional extensionality theorem is_valid_p_fix_fixed_eq {{body : (a → Result b) → a → Result b}} (Hvalid : ∀ f x, is_valid_p f (λ f => body f x)) : - ∀ x, fix body x = body (fix body) x := - fix_fixed_eq (is_valid_p_imp_is_valid Hvalid) + fix body = body (fix body) := by + apply funext + exact fix_fixed_eq (is_valid_p_imp_is_valid Hvalid) end Fix @@ -562,8 +565,8 @@ namespace Ex2 let y ← f (tl, i - 1) .ret y - theorem list_nth_body_valid: ∀ f x, is_valid_p f (λ f => @list_nth_body a f x) := by - intro f x + theorem list_nth_body_valid: ∀ k x, is_valid_p k (λ k => @list_nth_body a k x) := by + intro k x simp [list_nth_body] split <;> simp split <;> simp @@ -584,9 +587,8 @@ namespace Ex2 .ret y) := by have Heq := is_valid_p_fix_fixed_eq (@list_nth_body_valid a) - simp [Heq, list_nth] - conv => lhs; rw [list_nth_body] - simp [Heq] + simp [list_nth] + conv => lhs; rw [Heq] end Ex2 @@ -765,4 +767,73 @@ namespace Ex3 end Ex3 +namespace Ex4 + /- Higher-order example -/ + open Primitives Fix + + variable {a b : Type} + + /- An auxiliary function, which doesn't require the fixed-point -/ + def map (f : a → Result b) (ls : List a) : Result (List b) := + match ls with + | [] => .ret [] + | hd :: tl => + do + let hd ← f hd + let tl ← map f tl + .ret (hd :: tl) + + /- The validity theorem for `map`, generic in `f` -/ + /- TODO: rename the condition to k in all the lemma statements -/ + theorem map_is_valid + {{f : (a → Result b) → a → Result c}} + (Hfvalid : ∀ k x, is_valid_p k (λ k => f k x)) + (k : (a → Result b) → a → Result b) + (ls : List a) : + is_valid_p k (λ k => map (f k) ls) := by + induction ls <;> simp [map] + apply is_valid_p_bind <;> simp_all + intros + apply is_valid_p_bind <;> simp_all + + /- An example which uses map -/ + inductive Tree (a : Type) := + | leaf (x : a) + | node (tl : List (Tree a)) + + def id_body (f : Tree a → Result (Tree a)) (t : Tree a) : Result (Tree a) := + match t with + | .leaf x => .ret (.leaf x) + | .node tl => + do + let tl ← map f tl + .ret (.node tl) + + /- TODO: make the naming consistent (suffix with "_is") -/ + theorem id_body_is_valid : + ∀ k x, is_valid_p k (λ k => @id_body a k x) := by + intro k x + simp [id_body] + split <;> simp + apply is_valid_p_bind <;> simp_all + -- We have to show that `map k tl` is valid + apply map_is_valid; simp + + noncomputable def id (t : Tree a) := fix id_body t + + theorem id_eq (t : Tree a) : + (id t = + match t with + | .leaf x => .ret (.leaf x) + | .node tl => + do + let tl ← map id tl + .ret (.node tl)) + := by + have Heq := is_valid_p_fix_fixed_eq (@id_body_is_valid a) + simp [id] + conv => lhs; rw [Heq]; simp; rw [id_body] + +end Ex4 + end Diverge |