luau/prototyping/Properties/StrictMode.agda

{-# OPTIONS --rewriting #-}

module Properties.StrictMode where

import Agda.Builtin.Equality.Rewrite
open import Agda.Builtin.Equality using (_≡_; refl)
open import FFI.Data.Either using (Either; Left; Right; mapL; mapR; mapLR; swapLR; cond)
open import FFI.Data.Maybe using (Maybe; just; nothing)
open import Luau.Heap using (Heap; Object; function_is_end; defn; alloc; ok; next; lookup-not-allocated) renaming (_≡_⊕_↦_ to _≡ᴴ_⊕_↦_; _[_] to _[_]ᴴ; ∅ to ∅ᴴ)
open import Luau.StrictMode using (Warningᴱ; Warningᴮ; Warningᴼ; Warningᴴ; UnallocatedAddress; UnboundVariable; FunctionCallMismatch; app₁; app₂; BinOpMismatch₁; BinOpMismatch₂; bin₁; bin₂; BlockMismatch; block₁; return; LocalVarMismatch; local₁; local₂; FunctionDefnMismatch; function₁; function₂; heap; expr; block; addr)
open import Luau.Substitution using (_[_/_]ᴮ; _[_/_]ᴱ; _[_/_]ᴮunless_; var_[_/_]ᴱwhenever_)
open import Luau.Subtyping using (_≮:_; witness; unknown; never; scalar; function; scalar-function; scalar-function-ok; scalar-function-err; scalar-scalar; function-scalar; function-ok; function-err; left; right; _,_; Tree; Language; ¬Language)
open import Luau.Syntax using (Expr; yes; var; val; var_∈_; _⟨_⟩∈_; _$_; addr; number; bool; string; binexp; nil; function_is_end; block_is_end; done; return; local_←_; _∙_; fun; arg; name; ==; ~=)
open import Luau.FunctionTypes using (src; tgt)
open import Luau.Type using (Type; nil; number; boolean; string; _⇒_; never; unknown; _∩_; _∪_; _≡ᵀ_; _≡ᴹᵀ_)
open import Luau.TypeCheck using (_⊢ᴮ_∈_; _⊢ᴱ_∈_; _⊢ᴴᴮ_▷_∈_; _⊢ᴴᴱ_▷_∈_; nil; var; addr; app; function; block; done; return; local; orUnknown; srcBinOp; tgtBinOp)
open import Luau.Var using (_≡ⱽ_)
open import Luau.Addr using (_≡ᴬ_)
open import Luau.VarCtxt using (VarCtxt; ∅; _⋒_; _↦_; _⊕_↦_; _⊝_; ⊕-lookup-miss; ⊕-swap; ⊕-over) renaming (_[_] to _[_]ⱽ)
open import Luau.VarCtxt using (VarCtxt; ∅)
open import Properties.Remember using (remember; _,_)
open import Properties.Equality using (_≢_; sym; cong; trans; subst₁)
open import Properties.Dec using (Dec; yes; no)
open import Properties.Contradiction using (CONTRADICTION; ¬)
open import Properties.Functions using (_∘_)
open import Properties.FunctionTypes using (never-tgt-≮:; tgt-never-≮:; src-unknown-≮:; unknown-src-≮:)
open import Properties.Subtyping using (unknown-≮:; ≡-trans-≮:; ≮:-trans-≡; ≮:-trans; ≮:-refl; scalar-≢-impl-≮:; function-≮:-scalar; scalar-≮:-function; function-≮:-never; unknown-≮:-scalar; scalar-≮:-never; unknown-≮:-never)
open import Properties.TypeCheck using (typeOfᴼ; typeOfᴹᴼ; typeOfⱽ; typeOfᴱ; typeOfᴮ; typeCheckᴱ; typeCheckᴮ; typeCheckᴼ; typeCheckᴴ)
open import Luau.OpSem using (_⟦_⟧_⟶_; _⊢_⟶*_⊣_; _⊢_⟶ᴮ_⊣_; _⊢_⟶ᴱ_⊣_; app₁; app₂; function; beta; return; block; done; local; subst; binOp₀; binOp₁; binOp₂; refl; step; +; -; *; /; <; >; ==; ~=; <=; >=; ··)
open import Luau.RuntimeError using (BinOpError; RuntimeErrorᴱ; RuntimeErrorᴮ; FunctionMismatch; BinOpMismatch₁; BinOpMismatch₂; UnboundVariable; SEGV; app₁; app₂; bin₁; bin₂; block; local; return; +; -; *; /; <; >; <=; >=; ··)
open import Luau.RuntimeType using (RuntimeType; valueType; number; string; boolean; nil; function)

data _⊑_ (H : Heap yes) : Heap yes → Set where
  refl : (H ⊑ H)
  snoc : ∀ {H′ a O} → (H′ ≡ᴴ H ⊕ a ↦ O) → (H ⊑ H′)

rednᴱ⊑ : ∀ {H H′ M M′} → (H ⊢ M ⟶ᴱ M′ ⊣ H′) → (H ⊑ H′)
rednᴮ⊑ : ∀ {H H′ B B′} → (H ⊢ B ⟶ᴮ B′ ⊣ H′) → (H ⊑ H′)

rednᴱ⊑ (function a p) = snoc p
rednᴱ⊑ (app₁ s) = rednᴱ⊑ s
rednᴱ⊑ (app₂ p s) = rednᴱ⊑ s
rednᴱ⊑ (beta O v p q) = refl
rednᴱ⊑ (block s) = rednᴮ⊑ s
rednᴱ⊑ (return v) = refl
rednᴱ⊑ done = refl
rednᴱ⊑ (binOp₀ p) = refl
rednᴱ⊑ (binOp₁ s) = rednᴱ⊑ s
rednᴱ⊑ (binOp₂ s) = rednᴱ⊑ s

rednᴮ⊑ (local s) = rednᴱ⊑ s
rednᴮ⊑ (subst v) = refl
rednᴮ⊑ (function a p) = snoc p
rednᴮ⊑ (return s) = rednᴱ⊑ s

data LookupResult (H : Heap yes) a V : Set where
  just : (H [ a ]ᴴ ≡ just V) → LookupResult H a V
  nothing : (H [ a ]ᴴ ≡ nothing) → LookupResult H a V

lookup-⊑-nothing : ∀ {H H′} a → (H ⊑ H′) → (H′ [ a ]ᴴ ≡ nothing) → (H [ a ]ᴴ ≡ nothing)
lookup-⊑-nothing {H} a refl p = p
lookup-⊑-nothing {H} a (snoc defn) p with a ≡ᴬ next H 
lookup-⊑-nothing {H} a (snoc defn) p | yes refl = refl
lookup-⊑-nothing {H} a (snoc o) p | no q = trans (lookup-not-allocated o q) p

heap-weakeningᴱ : ∀ Γ H M {H′ U} → (H ⊑ H′) → (typeOfᴱ H′ Γ M ≮: U) → (typeOfᴱ H Γ M ≮: U)
heap-weakeningᴱ Γ H (var x) h p = p
heap-weakeningᴱ Γ H (val nil) h p = p
heap-weakeningᴱ Γ H (val (addr a)) refl p = p
heap-weakeningᴱ Γ H (val (addr a)) (snoc {a = b} q) p with a ≡ᴬ b
heap-weakeningᴱ Γ H (val (addr a)) (snoc {a = a} defn) p | yes refl = unknown-≮: p
heap-weakeningᴱ Γ H (val (addr a)) (snoc {a = b} q) p | no r = ≡-trans-≮: (cong orUnknown (cong typeOfᴹᴼ (lookup-not-allocated q r))) p
heap-weakeningᴱ Γ H (val (number x)) h p = p
heap-weakeningᴱ Γ H (val (bool x)) h p = p
heap-weakeningᴱ Γ H (val (string x)) h p = p
heap-weakeningᴱ Γ H (M $ N) h p = never-tgt-≮: (heap-weakeningᴱ Γ H M h (tgt-never-≮: p))
heap-weakeningᴱ Γ H (function f ⟨ var x ∈ T ⟩∈ U is B end) h p = p
heap-weakeningᴱ Γ H (block var b ∈ T is B end) h p = p
heap-weakeningᴱ Γ H (binexp M op N) h p = p

heap-weakeningᴮ : ∀ Γ H B {H′ U} → (H ⊑ H′) → (typeOfᴮ H′ Γ B ≮: U) → (typeOfᴮ H Γ B ≮: U)
heap-weakeningᴮ Γ H (function f ⟨ var x ∈ T ⟩∈ U is C end ∙ B) h p = heap-weakeningᴮ (Γ ⊕ f ↦ (T ⇒ U)) H B h p
heap-weakeningᴮ Γ H (local var x ∈ T ← M ∙ B) h p = heap-weakeningᴮ (Γ ⊕ x ↦ T) H B h p
heap-weakeningᴮ Γ H (return M ∙ B) h p = heap-weakeningᴱ Γ H M h p
heap-weakeningᴮ Γ H done h p = p

substitutivityᴱ : ∀ {Γ T U} H M v x → (typeOfᴱ H Γ (M [ v / x ]ᴱ) ≮: U) → Either (typeOfᴱ H (Γ ⊕ x ↦ T) M ≮: U) (typeOfᴱ H ∅ (val v) ≮: T)
substitutivityᴱ-whenever : ∀ {Γ T U} H v x y (r : Dec(x ≡ y)) → (typeOfᴱ H Γ (var y [ v / x ]ᴱwhenever r) ≮: U) → Either (typeOfᴱ H (Γ ⊕ x ↦ T) (var y) ≮: U) (typeOfᴱ H ∅ (val v) ≮: T)
substitutivityᴮ : ∀ {Γ T U} H B v x → (typeOfᴮ H Γ (B [ v / x ]ᴮ) ≮: U) → Either (typeOfᴮ H (Γ ⊕ x ↦ T) B ≮: U) (typeOfᴱ H ∅ (val v) ≮: T)
substitutivityᴮ-unless : ∀ {Γ T U V} H B v x y (r : Dec(x ≡ y)) → (typeOfᴮ H (Γ ⊕ y ↦ U) (B [ v / x ]ᴮunless r) ≮: V) → Either (typeOfᴮ H ((Γ ⊕ x ↦ T) ⊕ y ↦ U) B ≮: V) (typeOfᴱ H ∅ (val v) ≮: T)
substitutivityᴮ-unless-yes : ∀ {Γ Γ′ T V} H B v x y (r : x ≡ y) → (Γ′ ≡ Γ) → (typeOfᴮ H Γ (B [ v / x ]ᴮunless yes r) ≮: V) → Either (typeOfᴮ H Γ′ B ≮: V) (typeOfᴱ H ∅ (val v) ≮: T)
substitutivityᴮ-unless-no : ∀ {Γ Γ′ T V} H B v x y (r : x ≢ y) → (Γ′ ≡ Γ ⊕ x ↦ T) → (typeOfᴮ H Γ (B [ v / x ]ᴮunless no r) ≮: V) → Either (typeOfᴮ H Γ′ B ≮: V) (typeOfᴱ H ∅ (val v) ≮: T)

substitutivityᴱ H (var y) v x p = substitutivityᴱ-whenever H v x y (x ≡ⱽ y) p
substitutivityᴱ H (val w) v x p = Left p
substitutivityᴱ H (binexp M op N) v x p = Left p
substitutivityᴱ H (M $ N) v x p = mapL never-tgt-≮: (substitutivityᴱ H M v x (tgt-never-≮: p))
substitutivityᴱ H (function f ⟨ var y ∈ T ⟩∈ U is B end) v x p = Left p
substitutivityᴱ H (block var b ∈ T is B end) v x p = Left p
substitutivityᴱ-whenever H v x x (yes refl) q = swapLR (≮:-trans q)
substitutivityᴱ-whenever H v x y (no p) q = Left (≡-trans-≮: (cong orUnknown (sym (⊕-lookup-miss x y _ _ p))) q)

substitutivityᴮ H (function f ⟨ var y ∈ T ⟩∈ U is C end ∙ B) v x p = substitutivityᴮ-unless H B v x f (x ≡ⱽ f) p
substitutivityᴮ H (local var y ∈ T ← M ∙ B) v x p = substitutivityᴮ-unless H B v x y (x ≡ⱽ y) p
substitutivityᴮ H (return M ∙ B) v x p = substitutivityᴱ H M v x p
substitutivityᴮ H done v x p = Left p
substitutivityᴮ-unless H B v x y (yes p) q = substitutivityᴮ-unless-yes H B v x y p (⊕-over p) q
substitutivityᴮ-unless H B v x y (no p) q = substitutivityᴮ-unless-no H B v x y p (⊕-swap p) q
substitutivityᴮ-unless-yes H B v x y refl refl p = Left p
substitutivityᴮ-unless-no H B v x y p refl q = substitutivityᴮ H B v x q

binOpPreservation : ∀ H {op v w x} → (v ⟦ op ⟧ w ⟶ x) → (tgtBinOp op ≡ typeOfᴱ H ∅ (val x))
binOpPreservation H (+ m n) = refl
binOpPreservation H (- m n) = refl
binOpPreservation H (/ m n) = refl
binOpPreservation H (* m n) = refl
binOpPreservation H (< m n) = refl
binOpPreservation H (> m n) = refl
binOpPreservation H (<= m n) = refl
binOpPreservation H (>= m n) = refl
binOpPreservation H (== v w) = refl
binOpPreservation H (~= v w) = refl
binOpPreservation H (·· v w) = refl

reflect-subtypingᴱ : ∀ H M {H′ M′ T} → (H ⊢ M ⟶ᴱ M′ ⊣ H′) → (typeOfᴱ H′ ∅ M′ ≮: T) → Either (typeOfᴱ H ∅ M ≮: T) (Warningᴱ H (typeCheckᴱ H ∅ M))
reflect-subtypingᴮ : ∀ H B {H′ B′ T} → (H ⊢ B ⟶ᴮ B′ ⊣ H′) → (typeOfᴮ H′ ∅ B′ ≮: T) → Either (typeOfᴮ H ∅ B ≮: T) (Warningᴮ H (typeCheckᴮ H ∅ B))

reflect-subtypingᴱ H (M $ N) (app₁ s) p = mapLR never-tgt-≮: app₁ (reflect-subtypingᴱ H M s (tgt-never-≮: p))
reflect-subtypingᴱ H (M $ N) (app₂ v s) p = Left (never-tgt-≮: (heap-weakeningᴱ ∅ H M (rednᴱ⊑ s) (tgt-never-≮: p)))
reflect-subtypingᴱ H (M $ N) (beta (function f ⟨ var y ∈ T ⟩∈ U is B end) v refl q) p = Left (≡-trans-≮: (cong tgt (cong orUnknown (cong typeOfᴹᴼ q))) p)
reflect-subtypingᴱ H (function f ⟨ var x ∈ T ⟩∈ U is B end) (function a defn) p = Left p
reflect-subtypingᴱ H (block var b ∈ T is B end) (block s) p = Left p
reflect-subtypingᴱ H (block var b ∈ T is return (val v) ∙ B end) (return v) p = mapR BlockMismatch (swapLR (≮:-trans p))
reflect-subtypingᴱ H (block var b ∈ T is done end) done p = mapR BlockMismatch (swapLR (≮:-trans p))
reflect-subtypingᴱ H (binexp M op N) (binOp₀ s) p = Left (≡-trans-≮: (binOpPreservation H s) p)
reflect-subtypingᴱ H (binexp M op N) (binOp₁ s) p = Left p
reflect-subtypingᴱ H (binexp M op N) (binOp₂ s) p = Left p

reflect-subtypingᴮ H (function f ⟨ var x ∈ T ⟩∈ U is C end ∙ B) (function a defn) p = mapLR (heap-weakeningᴮ _ _ B (snoc defn)) (CONTRADICTION ∘ ≮:-refl) (substitutivityᴮ _ B (addr a) f p)
reflect-subtypingᴮ H (local var x ∈ T ← M ∙ B) (local s) p = Left (heap-weakeningᴮ (x ↦ T) H B (rednᴱ⊑ s) p)
reflect-subtypingᴮ H (local var x ∈ T ← M ∙ B) (subst v) p = mapR LocalVarMismatch (substitutivityᴮ H B v x p) 
reflect-subtypingᴮ H (return M ∙ B) (return s) p = mapR return (reflect-subtypingᴱ H M s p)

reflect-substitutionᴱ : ∀ {Γ T} H M v x → Warningᴱ H (typeCheckᴱ H Γ (M [ v / x ]ᴱ)) → Either (Warningᴱ H (typeCheckᴱ H (Γ ⊕ x ↦ T) M)) (Either (Warningᴱ H (typeCheckᴱ H ∅ (val v))) (typeOfᴱ H ∅ (val v) ≮: T))
reflect-substitutionᴱ-whenever : ∀ {Γ T} H v x y (p : Dec(x ≡ y)) → Warningᴱ H (typeCheckᴱ H Γ (var y [ v / x ]ᴱwhenever p)) → Either (Warningᴱ H (typeCheckᴱ H (Γ ⊕ x ↦ T) (var y))) (Either (Warningᴱ H (typeCheckᴱ H ∅ (val v))) (typeOfᴱ H ∅ (val v) ≮: T))
reflect-substitutionᴮ : ∀ {Γ T} H B v x → Warningᴮ H (typeCheckᴮ H Γ (B [ v / x ]ᴮ)) → Either (Warningᴮ H (typeCheckᴮ H (Γ ⊕ x ↦ T) B)) (Either (Warningᴱ H (typeCheckᴱ H ∅ (val v))) (typeOfᴱ H ∅ (val v) ≮: T))
reflect-substitutionᴮ-unless : ∀ {Γ T U} H B v x y (r : Dec(x ≡ y)) → Warningᴮ H (typeCheckᴮ H (Γ ⊕ y ↦ U) (B [ v / x ]ᴮunless r)) → Either (Warningᴮ H (typeCheckᴮ H ((Γ ⊕ x ↦ T) ⊕ y ↦ U) B)) (Either (Warningᴱ H (typeCheckᴱ H ∅ (val v))) (typeOfᴱ H ∅ (val v) ≮: T))
reflect-substitutionᴮ-unless-yes : ∀ {Γ Γ′ T} H B v x y (r : x ≡ y) → (Γ′ ≡ Γ) → Warningᴮ H (typeCheckᴮ H Γ (B [ v / x ]ᴮunless yes r)) → Either (Warningᴮ H (typeCheckᴮ H Γ′ B)) (Either (Warningᴱ H (typeCheckᴱ H ∅ (val v))) (typeOfᴱ H ∅ (val v) ≮: T))
reflect-substitutionᴮ-unless-no : ∀ {Γ Γ′ T} H B v x y (r : x ≢ y) → (Γ′ ≡ Γ ⊕ x ↦ T) → Warningᴮ H (typeCheckᴮ H Γ (B [ v / x ]ᴮunless no r)) → Either (Warningᴮ H (typeCheckᴮ H Γ′ B)) (Either (Warningᴱ H (typeCheckᴱ H ∅ (val v))) (typeOfᴱ H ∅ (val v) ≮: T))

reflect-substitutionᴱ H (var y) v x W = reflect-substitutionᴱ-whenever H v x y (x ≡ⱽ y) W
reflect-substitutionᴱ H (val (addr a)) v x (UnallocatedAddress r) = Left (UnallocatedAddress r)
reflect-substitutionᴱ H (M $ N) v x (FunctionCallMismatch p) with substitutivityᴱ H N v x p
reflect-substitutionᴱ H (M $ N) v x (FunctionCallMismatch p) | Right W = Right (Right W)
reflect-substitutionᴱ H (M $ N) v x (FunctionCallMismatch p) | Left q with substitutivityᴱ H M v x (src-unknown-≮: q)
reflect-substitutionᴱ H (M $ N) v x (FunctionCallMismatch p) | Left q | Left r = Left ((FunctionCallMismatch ∘ unknown-src-≮: q) r)
reflect-substitutionᴱ H (M $ N) v x (FunctionCallMismatch p) | Left q | Right W = Right (Right W)
reflect-substitutionᴱ H (M $ N) v x (app₁ W) = mapL app₁ (reflect-substitutionᴱ H M v x W)
reflect-substitutionᴱ H (M $ N) v x (app₂ W) = mapL app₂ (reflect-substitutionᴱ H N v x W)
reflect-substitutionᴱ H (function f ⟨ var y ∈ T ⟩∈ U is B end) v x (FunctionDefnMismatch q) = mapLR FunctionDefnMismatch Right (substitutivityᴮ-unless H B v x y (x ≡ⱽ y) q)
reflect-substitutionᴱ H (function f ⟨ var y ∈ T ⟩∈ U is B end) v x (function₁ W) = mapL function₁ (reflect-substitutionᴮ-unless H B v x y (x ≡ⱽ y) W)
reflect-substitutionᴱ H (block var b ∈ T is B end) v x (BlockMismatch q) =  mapLR BlockMismatch Right (substitutivityᴮ H B v x q)
reflect-substitutionᴱ H (block var b ∈ T is B end) v x (block₁ W′) = mapL block₁ (reflect-substitutionᴮ H B v x W′)
reflect-substitutionᴱ H (binexp M op N) v x (BinOpMismatch₁ q) = mapLR BinOpMismatch₁ Right (substitutivityᴱ H M v x q)
reflect-substitutionᴱ H (binexp M op N) v x (BinOpMismatch₂ q) = mapLR BinOpMismatch₂ Right (substitutivityᴱ H N v x q)
reflect-substitutionᴱ H (binexp M op N) v x (bin₁ W) = mapL bin₁ (reflect-substitutionᴱ H M v x W)
reflect-substitutionᴱ H (binexp M op N) v x (bin₂ W) = mapL bin₂ (reflect-substitutionᴱ H N v x W)

reflect-substitutionᴱ-whenever H a x x (yes refl) (UnallocatedAddress p) = Right (Left (UnallocatedAddress p))
reflect-substitutionᴱ-whenever H v x y (no p) (UnboundVariable q) = Left (UnboundVariable (trans (sym (⊕-lookup-miss x y _ _ p)) q))

reflect-substitutionᴮ H (function f ⟨ var y ∈ T ⟩∈ U is C end ∙ B) v x (FunctionDefnMismatch q) = mapLR FunctionDefnMismatch Right (substitutivityᴮ-unless H C v x y (x ≡ⱽ y) q)
reflect-substitutionᴮ H (function f ⟨ var y ∈ T ⟩∈ U is C end ∙ B) v x (function₁ W) =  mapL function₁ (reflect-substitutionᴮ-unless H C v x y (x ≡ⱽ y) W)
reflect-substitutionᴮ H (function f ⟨ var y ∈ T ⟩∈ U is C end ∙ B) v x (function₂ W) = mapL function₂ (reflect-substitutionᴮ-unless H B v x f (x ≡ⱽ f) W)
reflect-substitutionᴮ H (local var y ∈ T ← M ∙ B) v x (LocalVarMismatch q) = mapLR LocalVarMismatch Right (substitutivityᴱ H M v x q)
reflect-substitutionᴮ H (local var y ∈ T ← M ∙ B) v x (local₁ W) = mapL local₁ (reflect-substitutionᴱ H M v x W)
reflect-substitutionᴮ H (local var y ∈ T ← M ∙ B) v x (local₂ W) = mapL local₂ (reflect-substitutionᴮ-unless H B v x y (x ≡ⱽ y) W)
reflect-substitutionᴮ H (return M ∙ B) v x (return W) = mapL return (reflect-substitutionᴱ H M v x W)

reflect-substitutionᴮ-unless H B v x y (yes p) W = reflect-substitutionᴮ-unless-yes H B v x y p (⊕-over p) W
reflect-substitutionᴮ-unless H B v x y (no p) W = reflect-substitutionᴮ-unless-no H B v x y p (⊕-swap p) W
reflect-substitutionᴮ-unless-yes H B v x x refl refl W = Left W
reflect-substitutionᴮ-unless-no H B v x y p refl W = reflect-substitutionᴮ H B v x W

reflect-weakeningᴱ : ∀ Γ H M {H′} → (H ⊑ H′) → Warningᴱ H′ (typeCheckᴱ H′ Γ M) → Warningᴱ H (typeCheckᴱ H Γ M)
reflect-weakeningᴮ : ∀ Γ H B {H′} → (H ⊑ H′) → Warningᴮ H′ (typeCheckᴮ H′ Γ B) → Warningᴮ H (typeCheckᴮ H Γ B)

reflect-weakeningᴱ Γ H (var x) h (UnboundVariable p) = (UnboundVariable p)
reflect-weakeningᴱ Γ H (val (addr a)) h (UnallocatedAddress p) = UnallocatedAddress (lookup-⊑-nothing a h p)
reflect-weakeningᴱ Γ H (M $ N) h (FunctionCallMismatch p) = FunctionCallMismatch (heap-weakeningᴱ Γ H N h (unknown-src-≮: p (heap-weakeningᴱ Γ H M h (src-unknown-≮: p))))
reflect-weakeningᴱ Γ H (M $ N) h (app₁ W) = app₁ (reflect-weakeningᴱ Γ H M h W)
reflect-weakeningᴱ Γ H (M $ N) h (app₂ W) = app₂ (reflect-weakeningᴱ Γ H N h W)
reflect-weakeningᴱ Γ H (binexp M op N) h (BinOpMismatch₁ p) = BinOpMismatch₁ (heap-weakeningᴱ Γ H M h p)
reflect-weakeningᴱ Γ H (binexp M op N) h (BinOpMismatch₂ p) = BinOpMismatch₂ (heap-weakeningᴱ Γ H N h p)
reflect-weakeningᴱ Γ H (binexp M op N) h (bin₁ W′) = bin₁ (reflect-weakeningᴱ Γ H M h W′)
reflect-weakeningᴱ Γ H (binexp M op N) h (bin₂ W′) = bin₂ (reflect-weakeningᴱ Γ H N h W′)
reflect-weakeningᴱ Γ H (function f ⟨ var y ∈ T ⟩∈ U is B end) h (FunctionDefnMismatch p) = FunctionDefnMismatch (heap-weakeningᴮ (Γ ⊕ y ↦ T) H B h p)
reflect-weakeningᴱ Γ H (function f ⟨ var y ∈ T ⟩∈ U is B end) h (function₁ W) = function₁ (reflect-weakeningᴮ (Γ ⊕ y ↦ T) H B h W)
reflect-weakeningᴱ Γ H (block var b ∈ T is B end) h (BlockMismatch p) = BlockMismatch (heap-weakeningᴮ Γ H B h p)
reflect-weakeningᴱ Γ H (block var b ∈ T is B end) h (block₁ W) = block₁ (reflect-weakeningᴮ Γ H B h W)

reflect-weakeningᴮ Γ H (return M ∙ B) h (return W) = return (reflect-weakeningᴱ Γ H M h W)
reflect-weakeningᴮ Γ H (local var y ∈ T ← M ∙ B) h (LocalVarMismatch p) = LocalVarMismatch (heap-weakeningᴱ Γ H M h p)
reflect-weakeningᴮ Γ H (local var y ∈ T ← M ∙ B) h (local₁ W) = local₁ (reflect-weakeningᴱ Γ H M h W)
reflect-weakeningᴮ Γ H (local var y ∈ T ← M ∙ B) h (local₂ W) = local₂ (reflect-weakeningᴮ (Γ ⊕ y ↦ T) H B h W)
reflect-weakeningᴮ Γ H (function f ⟨ var x ∈ T ⟩∈ U is C end ∙ B) h (FunctionDefnMismatch p) = FunctionDefnMismatch (heap-weakeningᴮ (Γ ⊕ x ↦ T) H C h p)
reflect-weakeningᴮ Γ H (function f ⟨ var x ∈ T ⟩∈ U is C end ∙ B) h (function₁ W) = function₁ (reflect-weakeningᴮ (Γ ⊕ x ↦ T) H C h W)
reflect-weakeningᴮ Γ H (function f ⟨ var x ∈ T ⟩∈ U is C end ∙ B) h (function₂ W) = function₂ (reflect-weakeningᴮ (Γ ⊕ f ↦ (T ⇒ U)) H B h W)

reflect-weakeningᴼ : ∀ H O {H′} → (H ⊑ H′) → Warningᴼ H′ (typeCheckᴼ H′ O) → Warningᴼ H (typeCheckᴼ H O)
reflect-weakeningᴼ H (just function f ⟨ var x ∈ T ⟩∈ U is B end) h (FunctionDefnMismatch p) = FunctionDefnMismatch (heap-weakeningᴮ (x ↦ T) H B h p)
reflect-weakeningᴼ H (just function f ⟨ var x ∈ T ⟩∈ U is B end) h (function₁ W) = function₁ (reflect-weakeningᴮ (x ↦ T) H B h W)

reflectᴱ : ∀ H M {H′ M′} → (H ⊢ M ⟶ᴱ M′ ⊣ H′) → Warningᴱ H′ (typeCheckᴱ H′ ∅ M′) → Either (Warningᴱ H (typeCheckᴱ H ∅ M)) (Warningᴴ H (typeCheckᴴ H))
reflectᴮ : ∀ H B {H′ B′} → (H ⊢ B ⟶ᴮ B′ ⊣ H′) → Warningᴮ H′ (typeCheckᴮ H′ ∅ B′) → Either (Warningᴮ H (typeCheckᴮ H ∅ B)) (Warningᴴ H (typeCheckᴴ H))

reflectᴱ H (M $ N) (app₁ s) (FunctionCallMismatch p) = cond (Left ∘ FunctionCallMismatch ∘ heap-weakeningᴱ ∅ H N (rednᴱ⊑ s) ∘ unknown-src-≮: p) (Left ∘ app₁) (reflect-subtypingᴱ H M s (src-unknown-≮: p))
reflectᴱ H (M $ N) (app₁ s) (app₁ W′) = mapL app₁ (reflectᴱ H M s W′)
reflectᴱ H (M $ N) (app₁ s) (app₂ W′) = Left (app₂ (reflect-weakeningᴱ ∅ H N (rednᴱ⊑ s) W′))
reflectᴱ H (M $ N) (app₂ p s) (FunctionCallMismatch q) = cond (λ r → Left (FunctionCallMismatch (unknown-src-≮: r (heap-weakeningᴱ ∅ H M (rednᴱ⊑ s) (src-unknown-≮: r))))) (Left ∘ app₂) (reflect-subtypingᴱ H N s q)
reflectᴱ H (M $ N) (app₂ p s) (app₁ W′) = Left (app₁ (reflect-weakeningᴱ ∅ H M (rednᴱ⊑ s) W′))
reflectᴱ H (M $ N) (app₂ p s) (app₂ W′) = mapL app₂ (reflectᴱ H N s W′)
reflectᴱ H (val (addr a) $ N) (beta (function f ⟨ var x ∈ T ⟩∈ U is B end) v refl p) (BlockMismatch q) with substitutivityᴮ H B v x q 
reflectᴱ H (val (addr a) $ N) (beta (function f ⟨ var x ∈ T ⟩∈ U is B end) v refl p) (BlockMismatch q) | Left r = Right (addr a p (FunctionDefnMismatch r))
reflectᴱ H (val (addr a) $ N) (beta (function f ⟨ var x ∈ T ⟩∈ U is B end) v refl p) (BlockMismatch q) | Right r = Left (FunctionCallMismatch (≮:-trans-≡ r ((cong src (cong orUnknown (cong typeOfᴹᴼ (sym p)))))))
reflectᴱ H (val (addr a) $ N) (beta (function f ⟨ var x ∈ T ⟩∈ U is B end) v refl p) (block₁ W′) with reflect-substitutionᴮ _ B v x W′
reflectᴱ H (val (addr a) $ N) (beta (function f ⟨ var x ∈ T ⟩∈ U is B end) v refl p) (block₁ W′) | Left W = Right (addr a p (function₁ W))
reflectᴱ H (val (addr a) $ N) (beta (function f ⟨ var x ∈ T ⟩∈ U is B end) v refl p) (block₁ W′) | Right (Left W) = Left (app₂ W)
reflectᴱ H (val (addr a) $ N) (beta (function f ⟨ var x ∈ T ⟩∈ U is B end) v refl p) (block₁ W′) | Right (Right q) = Left (FunctionCallMismatch (≮:-trans-≡ q (cong src (cong orUnknown (cong typeOfᴹᴼ (sym p))))))
reflectᴱ H (block var b ∈ T is B end) (block s) (BlockMismatch p) = Left (cond BlockMismatch block₁ (reflect-subtypingᴮ H B s p))
reflectᴱ H (block var b ∈ T is B end) (block s) (block₁ W′) = mapL block₁ (reflectᴮ H B s W′)
reflectᴱ H (block var b ∈ T is B end) (return v) W′ = Left (block₁ (return W′))
reflectᴱ H (function f ⟨ var x ∈ T ⟩∈ U is B end) (function a defn) (UnallocatedAddress ())
reflectᴱ H (binexp M op N) (binOp₀ ()) (UnallocatedAddress p)
reflectᴱ H (binexp M op N) (binOp₁ s) (BinOpMismatch₁ p) = Left (cond BinOpMismatch₁ bin₁ (reflect-subtypingᴱ H M s p))
reflectᴱ H (binexp M op N) (binOp₁ s) (BinOpMismatch₂ p) = Left (BinOpMismatch₂ (heap-weakeningᴱ ∅ H N (rednᴱ⊑ s) p))
reflectᴱ H (binexp M op N) (binOp₁ s) (bin₁ W′) = mapL bin₁ (reflectᴱ H M s W′)
reflectᴱ H (binexp M op N) (binOp₁ s) (bin₂ W′) = Left (bin₂ (reflect-weakeningᴱ ∅ H N (rednᴱ⊑ s) W′))
reflectᴱ H (binexp M op N) (binOp₂ s) (BinOpMismatch₁ p) = Left (BinOpMismatch₁ (heap-weakeningᴱ ∅ H M (rednᴱ⊑ s) p))
reflectᴱ H (binexp M op N) (binOp₂ s) (BinOpMismatch₂ p) = Left (cond BinOpMismatch₂ bin₂ (reflect-subtypingᴱ H N s p))
reflectᴱ H (binexp M op N) (binOp₂ s) (bin₁ W′) = Left (bin₁ (reflect-weakeningᴱ ∅ H M (rednᴱ⊑ s) W′))
reflectᴱ H (binexp M op N) (binOp₂ s) (bin₂ W′) = mapL bin₂ (reflectᴱ H N s W′)

reflectᴮ H (local var x ∈ T ← M ∙ B) (local s) (LocalVarMismatch p) = Left (cond LocalVarMismatch local₁ (reflect-subtypingᴱ H M s p))
reflectᴮ H (local var x ∈ T ← M ∙ B) (local s) (local₁ W′) = mapL local₁ (reflectᴱ H M s W′)
reflectᴮ H (local var x ∈ T ← M ∙ B) (local s) (local₂ W′) = Left (local₂ (reflect-weakeningᴮ (x ↦ T) H B (rednᴱ⊑ s) W′))
reflectᴮ H (local var x ∈ T ← M ∙ B) (subst v) W′ = Left (cond local₂ (cond local₁ LocalVarMismatch) (reflect-substitutionᴮ H B v x W′))
reflectᴮ H (function f ⟨ var y ∈ T ⟩∈ U is C end ∙ B) (function a defn) W′ with reflect-substitutionᴮ _ B (addr a) f W′
reflectᴮ H (function f ⟨ var y ∈ T ⟩∈ U is C end ∙ B) (function a defn) W′ | Left W = Left (function₂ (reflect-weakeningᴮ (f ↦ (T ⇒ U)) H B (snoc defn) W))
reflectᴮ H (function f ⟨ var y ∈ T ⟩∈ U is C end ∙ B) (function a defn) W′ | Right (Left (UnallocatedAddress ()))
reflectᴮ H (function f ⟨ var y ∈ T ⟩∈ U is C end ∙ B) (function a defn) W′ | Right (Right p) = CONTRADICTION (≮:-refl p)
reflectᴮ H (return M ∙ B) (return s) (return W′) = mapL return (reflectᴱ H M s W′)

reflectᴴᴱ : ∀ H M {H′ M′} → (H ⊢ M ⟶ᴱ M′ ⊣ H′) → Warningᴴ H′ (typeCheckᴴ H′) → Either (Warningᴱ H (typeCheckᴱ H ∅ M)) (Warningᴴ H (typeCheckᴴ H))
reflectᴴᴮ : ∀ H B {H′ B′} → (H ⊢ B ⟶ᴮ B′ ⊣ H′) → Warningᴴ H′ (typeCheckᴴ H′) → Either (Warningᴮ H (typeCheckᴮ H ∅ B)) (Warningᴴ H (typeCheckᴴ H))

reflectᴴᴱ H (M $ N) (app₁ s) W = mapL app₁ (reflectᴴᴱ H M s W)
reflectᴴᴱ H (M $ N) (app₂ v s) W = mapL app₂ (reflectᴴᴱ H N s W)
reflectᴴᴱ H (M $ N) (beta O v refl p) W = Right W
reflectᴴᴱ H (function f ⟨ var x ∈ T ⟩∈ U is B end) (function a p) (addr b refl W) with b ≡ᴬ a
reflectᴴᴱ H (function f ⟨ var x ∈ T ⟩∈ U is B end) (function a defn) (addr b refl (FunctionDefnMismatch p)) | yes refl = Left (FunctionDefnMismatch (heap-weakeningᴮ (x ↦ T) H B (snoc defn) p))
reflectᴴᴱ H (function f ⟨ var x ∈ T ⟩∈ U is B end) (function a defn) (addr b refl (function₁ W)) | yes refl = Left (function₁ (reflect-weakeningᴮ (x ↦ T) H B (snoc defn) W))
reflectᴴᴱ H (function f ⟨ var x ∈ T ⟩∈ U is B end) (function a p) (addr b refl W) | no q = Right (addr b (lookup-not-allocated p q) (reflect-weakeningᴼ H _ (snoc p) W))
reflectᴴᴱ H (block var b ∈ T is B end) (block s) W = mapL block₁ (reflectᴴᴮ H B s W)
reflectᴴᴱ H (block var b ∈ T is return (val v) ∙ B end) (return v) W = Right W
reflectᴴᴱ H (block var b ∈ T is done end) done W = Right W
reflectᴴᴱ H (binexp M op N) (binOp₀ s) W = Right W
reflectᴴᴱ H (binexp M op N) (binOp₁ s) W = mapL bin₁ (reflectᴴᴱ H M s W)
reflectᴴᴱ H (binexp M op N) (binOp₂ s) W = mapL bin₂ (reflectᴴᴱ H N s W)

reflectᴴᴮ H (function f ⟨ var x ∈ T ⟩∈ U is C end ∙ B) (function a p) (addr b refl W) with b ≡ᴬ a
reflectᴴᴮ H (function f ⟨ var x ∈ T ⟩∈ U is C end ∙ B) (function a defn) (addr b refl (FunctionDefnMismatch p)) | yes refl = Left (FunctionDefnMismatch (heap-weakeningᴮ (x ↦ T) H C (snoc defn) p))
reflectᴴᴮ H (function f ⟨ var x ∈ T ⟩∈ U is C end ∙ B) (function a defn) (addr b refl (function₁ W)) | yes refl = Left (function₁ (reflect-weakeningᴮ (x ↦ T) H C (snoc defn) W))
reflectᴴᴮ H (function f ⟨ var x ∈ T ⟩∈ U is C end ∙ B) (function a p) (addr b refl W) | no q = Right (addr b (lookup-not-allocated p q) (reflect-weakeningᴼ H _ (snoc p) W))
reflectᴴᴮ H (local var x ∈ T ← M ∙ B) (local s) W = mapL local₁ (reflectᴴᴱ H M s W)
reflectᴴᴮ H (local var x ∈ T ← M ∙ B) (subst v) W = Right W
reflectᴴᴮ H (return M ∙ B) (return s) W = mapL return (reflectᴴᴱ H M s W)

reflect* : ∀ H B {H′ B′} → (H ⊢ B ⟶* B′ ⊣ H′) → Either (Warningᴮ H′ (typeCheckᴮ H′ ∅ B′)) (Warningᴴ H′ (typeCheckᴴ H′)) → Either (Warningᴮ H (typeCheckᴮ H ∅ B)) (Warningᴴ H (typeCheckᴴ H))
reflect* H B refl W = W
reflect* H B (step s t) W = cond (reflectᴮ H B s) (reflectᴴᴮ H B s) (reflect* _ _ t W)

isntNumber : ∀ H v → (valueType v ≢ number) → (typeOfᴱ H ∅ (val v) ≮: number)
isntNumber H nil p = scalar-≢-impl-≮: nil number (λ ())
isntNumber H (addr a) p with remember (H [ a ]ᴴ)
isntNumber H (addr a) p | (just (function f ⟨ var x ∈ T ⟩∈ U is B end) , q) = ≡-trans-≮: (cong orUnknown (cong typeOfᴹᴼ q)) (function-≮:-scalar number)
isntNumber H (addr a) p | (nothing , q) = ≡-trans-≮: (cong orUnknown (cong typeOfᴹᴼ q)) (unknown-≮:-scalar number)
isntNumber H (number x) p = CONTRADICTION (p refl)
isntNumber H (bool x) p = scalar-≢-impl-≮: boolean number (λ ())
isntNumber H (string x) p = scalar-≢-impl-≮: string number (λ ())

isntString : ∀ H v → (valueType v ≢ string) → (typeOfᴱ H ∅ (val v) ≮: string)
isntString H nil p = scalar-≢-impl-≮: nil string (λ ())
isntString H (addr a) p with remember (H [ a ]ᴴ)
isntString H (addr a) p | (just (function f ⟨ var x ∈ T ⟩∈ U is B end) , q) = ≡-trans-≮: (cong orUnknown (cong typeOfᴹᴼ q)) (function-≮:-scalar string)
isntString H (addr a) p | (nothing , q) = ≡-trans-≮: (cong orUnknown (cong typeOfᴹᴼ q)) (unknown-≮:-scalar string)
isntString H (number x) p = scalar-≢-impl-≮: number string (λ ())
isntString H (bool x) p = scalar-≢-impl-≮: boolean string (λ ())
isntString H (string x) p = CONTRADICTION (p refl)

isntFunction : ∀ H v {T U} → (valueType v ≢ function) → (typeOfᴱ H ∅ (val v) ≮: (T ⇒ U))
isntFunction H nil p = scalar-≮:-function nil
isntFunction H (addr a) p = CONTRADICTION (p refl)
isntFunction H (number x) p = scalar-≮:-function number
isntFunction H (bool x) p = scalar-≮:-function boolean
isntFunction H (string x) p = scalar-≮:-function string

isntEmpty : ∀ H v → (typeOfᴱ H ∅ (val v) ≮: never)
isntEmpty H nil = scalar-≮:-never nil
isntEmpty H (addr a) with remember (H [ a ]ᴴ)
isntEmpty H (addr a) | (just (function f ⟨ var x ∈ T ⟩∈ U is B end) , p) = ≡-trans-≮: (cong orUnknown (cong typeOfᴹᴼ p)) function-≮:-never
isntEmpty H (addr a) | (nothing , p) = ≡-trans-≮: (cong orUnknown (cong typeOfᴹᴼ p)) unknown-≮:-never
isntEmpty H (number x) = scalar-≮:-never number
isntEmpty H (bool x) = scalar-≮:-never boolean
isntEmpty H (string x) = scalar-≮:-never string

runtimeBinOpWarning : ∀ H {op} v → BinOpError op (valueType v) → (typeOfᴱ H ∅ (val v) ≮: srcBinOp op)
runtimeBinOpWarning H v (+ p) = isntNumber H v p
runtimeBinOpWarning H v (- p) = isntNumber H v p
runtimeBinOpWarning H v (* p) = isntNumber H v p
runtimeBinOpWarning H v (/ p) = isntNumber H v p
runtimeBinOpWarning H v (< p) = isntNumber H v p
runtimeBinOpWarning H v (> p) = isntNumber H v p
runtimeBinOpWarning H v (<= p) = isntNumber H v p
runtimeBinOpWarning H v (>= p) = isntNumber H v p
runtimeBinOpWarning H v (·· p) = isntString H v p

runtimeWarningᴱ : ∀ H M → RuntimeErrorᴱ H M → Warningᴱ H (typeCheckᴱ H ∅ M)
runtimeWarningᴮ : ∀ H B → RuntimeErrorᴮ H B → Warningᴮ H (typeCheckᴮ H ∅ B)

runtimeWarningᴱ H (var x) UnboundVariable = UnboundVariable refl
runtimeWarningᴱ H (val (addr a)) (SEGV p) = UnallocatedAddress p
runtimeWarningᴱ H (M $ N) (FunctionMismatch v w p) = FunctionCallMismatch (unknown-src-≮: (isntEmpty H w) (isntFunction H v p))
runtimeWarningᴱ H (M $ N) (app₁ err) = app₁ (runtimeWarningᴱ H M err)
runtimeWarningᴱ H (M $ N) (app₂ err) = app₂ (runtimeWarningᴱ H N err)
runtimeWarningᴱ H (block var b ∈ T is B end) (block err) = block₁ (runtimeWarningᴮ H B err)
runtimeWarningᴱ H (binexp M op N) (BinOpMismatch₁ v w p) = BinOpMismatch₁ (runtimeBinOpWarning H v p)
runtimeWarningᴱ H (binexp M op N) (BinOpMismatch₂ v w p) = BinOpMismatch₂ (runtimeBinOpWarning H w p)
runtimeWarningᴱ H (binexp M op N) (bin₁ err) = bin₁ (runtimeWarningᴱ H M err)
runtimeWarningᴱ H (binexp M op N) (bin₂ err) = bin₂ (runtimeWarningᴱ H N err)

runtimeWarningᴮ H (local var x ∈ T ← M ∙ B) (local err) = local₁ (runtimeWarningᴱ H M err)
runtimeWarningᴮ H (return M ∙ B) (return err) = return (runtimeWarningᴱ H M err)

wellTypedProgramsDontGoWrong : ∀ H′ B B′ → (∅ᴴ ⊢ B ⟶* B′ ⊣ H′) → (RuntimeErrorᴮ H′ B′) → Warningᴮ ∅ᴴ (typeCheckᴮ ∅ᴴ ∅ B)
wellTypedProgramsDontGoWrong H′ B B′ t err with reflect* ∅ᴴ B t (Left (runtimeWarningᴮ H′ B′ err))
wellTypedProgramsDontGoWrong H′ B B′ t err | Right (addr a refl ())
wellTypedProgramsDontGoWrong H′ B B′ t err | Left W = W