quox/lib/Quox/Equal.idr

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module Quox.Equal
import public Quox.Typing
import public Control.Monad.Either
import public Control.Monad.Reader
import Data.Maybe
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public export
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record CmpContext where
constructor MkCmpContext
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mode : EqMode
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public export
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0 HasCmpContext : (Type -> Type) -> Type
HasCmpContext = MonadReader CmpContext
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public export
0 CanEqual : (q : Type) -> (Type -> Type) -> Type
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CanEqual q m = (HasErr q m, HasCmpContext m)
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private %inline
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mode : HasCmpContext m => m EqMode
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mode = asks mode
private %inline
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clashT : CanEqual q m => Term q d n -> Term q d n -> Term q d n -> m a
clashT ty s t = throwError $ ClashT !mode ty s t
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private %inline
clashE : CanEqual q m => Elim q d n -> Elim q d n -> m a
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clashE e f = throwError $ ClashE !mode e f
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||| true if a term is syntactically a type, or is neutral.
|||
||| this function *doesn't* push substitutions, because its main use is as a
||| `So` argument to skip cases that are already known to be nonsense. and
||| the substitutions have already been pushed.
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public export %inline
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isTyCon : (t : Term {}) -> Bool
isTyCon (TYPE {}) = True
isTyCon (Pi {}) = True
isTyCon (Lam {}) = False
isTyCon (Sig {}) = True
isTyCon (Pair {}) = False
isTyCon (Eq {}) = True
isTyCon (DLam {}) = False
isTyCon (E {}) = True
isTyCon (CloT {}) = False
isTyCon (DCloT {}) = False
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public export %inline
sameTyCon : (s, t : Term q d n) ->
(0 ts : So (isTyCon s)) => (0 tt : So (isTyCon t)) =>
Bool
sameTyCon (TYPE {}) (TYPE {}) = True
sameTyCon (TYPE {}) _ = False
sameTyCon (Pi {}) (Pi {}) = True
sameTyCon (Pi {}) _ = False
sameTyCon (Sig {}) (Sig {}) = True
sameTyCon (Sig {}) _ = False
sameTyCon (Eq {}) (Eq {}) = True
sameTyCon (Eq {}) _ = False
sameTyCon (E {}) (E {}) = True
sameTyCon (E {}) _ = False
parameters (defs : Definitions' q g)
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||| true if a type is known to be a subsingleton purely by its form.
||| a subsingleton is a type with only zero or one possible values.
||| equality/subtyping accepts immediately on values of subsingleton types.
|||
||| * a function type is a subsingleton if its codomain is.
||| * a pair type is a subsingleton if both its elements are.
||| * all equality types are subsingletons because uip is admissible by
||| boundary separation.
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public export
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isSubSing : Term q 0 n -> Bool
isSubSing ty =
let Element ty nc = whnf defs ty in
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case ty of
TYPE _ => False
Pi {res, _} => isSubSing res.term
Lam {} => False
Sig {fst, snd, _} => isSubSing fst && isSubSing snd.term
Pair {} => False
Eq {} => True
DLam {} => False
E (s :# _) => isSubSing s
E _ => False
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parameters {auto _ : HasErr q m}
export %inline
ensure : (a -> Error q) -> (p : a -> Bool) -> (t : a) -> m (So (p t))
ensure e p t = case nchoose $ p t of
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Left y => pure y
Right _ => throwError $ e t
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export %inline
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ensureTyCon : HasErr q m => (t : Term q d n) -> m (So (isTyCon t))
ensureTyCon = ensure NotType isTyCon
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parameters (defs : Definitions' q _) {auto _ : (CanEqual q m, Eq q)}
mutual
namespace Term
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||| `compare0 ctx ty s t` compares `s` and `t` at type `ty`, according to
||| the current variance `mode`.
|||
||| ⚠ **assumes that `s`, `t` have already been checked against `ty`**. ⚠
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export covering %inline
compare0 : TContext q 0 n -> (ty, s, t : Term q 0 n) -> m ()
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compare0 ctx ty s t =
wrapErr (WhileComparingT (MkTyContext new ctx) !mode ty s t) $ do
let Element ty nty = whnf defs ty
Element s ns = whnf defs s
Element t nt = whnf defs t
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tty <- ensureTyCon ty
compare0' ctx ty s t
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||| converts an elim "Γ ⊢ e" to "Γ, x ⊢ e x", for comparing with
||| a lambda "Γ ⊢ λx ⇒ t" that has been converted to "Γ, x ⊢ t".
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private %inline
toLamBody : Elim q d n -> Term q d (S n)
toLamBody e = E $ weakE e :@ BVT 0
private covering
compare0' : TContext q 0 n ->
(ty, s, t : Term q 0 n) ->
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(0 nty : NotRedex defs ty) => (0 tty : So (isTyCon ty)) =>
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(0 ns : NotRedex defs s) => (0 nt : NotRedex defs t) =>
m ()
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compare0' ctx (TYPE _) s t = compareType ctx s t
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compare0' ctx ty@(Pi {arg, res, _}) s t {n} = local {mode := Equal} $
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case (s, t) of
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-- Γ, x : A ⊢ s = t : B
-- -----------------------------------------
-- Γ ⊢ (λx ⇒ s) = (λx ⇒ t) : (π·x : A) → B
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(Lam _ b1, Lam _ b2) => compare0 ctx' res.term b1.term b2.term
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-- Γ, x : A ⊢ s = e x : B
-- ----------------------------------
-- Γ ⊢ (λx ⇒ s) = e : (π·x : A) → B
(E e, Lam _ b) => eta e b
(Lam _ b, E e) => eta e b
(E e, E f) => Elim.compare0 ctx e f
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_ => throwError $ WrongType ty s t
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where
ctx' : TContext q 0 (S n)
ctx' = ctx :< arg
eta : Elim q 0 n -> ScopeTerm q 0 n -> m ()
eta e (TUsed b) = compare0 ctx' res.term (toLamBody e) b
eta e (TUnused _) = clashT ty s t
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compare0' ctx ty@(Sig {fst, snd, _}) s t = local {mode := Equal} $
case (s, t) of
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-- Γ ⊢ s₁ = t₁ : A Γ ⊢ s₂ = t₂ : B{s₁/x}
-- -------------------------------------------
-- Γ ⊢ (s₁,t₁) = (s₂,t₂) : (x : A) × B
--
-- [todo] η for π ≥ 0 maybe
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(Pair sFst sSnd, Pair tFst tSnd) => do
compare0 ctx fst sFst tFst
compare0 ctx (sub1 snd (sFst :# fst)) sSnd tSnd
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_ => throwError $ WrongType ty s t
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compare0' _ (Eq {}) _ _ =
-- ✨ uip ✨
--
-- Γ ⊢ e = f : Eq [i ⇒ A] s t
pure ()
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compare0' ctx ty@(E _) s t = do
-- a neutral type can only be inhabited by neutral values
-- e.g. an abstract value in an abstract type, bound variables, …
E e <- pure s | _ => throwError $ WrongType ty s t
E f <- pure t | _ => throwError $ WrongType ty s t
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Elim.compare0 ctx e f
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||| compares two types, using the current variance `mode` for universes.
||| fails if they are not types, even if they would happen to be equal.
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export covering %inline
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compareType : TContext q 0 n -> (s, t : Term q 0 n) -> m ()
compareType ctx s t = do
let Element s ns = whnf defs s
Element t nt = whnf defs t
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ts <- ensureTyCon s
tt <- ensureTyCon t
st <- either pure (const $ clashT (TYPE UAny) s t) $
nchoose $ sameTyCon s t
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compareType' ctx s t
private covering
compareType' : TContext q 0 n -> (s, t : Term q 0 n) ->
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(0 ns : NotRedex defs s) => (0 ts : So (isTyCon s)) =>
(0 nt : NotRedex defs t) => (0 tt : So (isTyCon t)) =>
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(0 st : So (sameTyCon s t)) =>
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m ()
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-- equality is the same as subtyping, except with the
-- "≤" in the TYPE rule being replaced with "="
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compareType' ctx (TYPE k) (TYPE l) =
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-- 𝓀
-- ----------------------
-- Γ ⊢ Type 𝓀 <: Type
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expectModeU !mode k l
compareType' ctx (Pi {qty = sQty, arg = sArg, res = sRes, _})
(Pi {qty = tQty, arg = tArg, res = tRes, _}) = do
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-- Γ ⊢ A₁ :> A₂ Γ, x : A₁ ⊢ B₁ <: B₂
-- ----------------------------------------
-- Γ ⊢ (π·x : A₁) → B₁ <: (π·x : A₂) → B₂
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expectEqualQ sQty tQty
local {mode $= flip} $ compareType ctx sArg tArg -- contra
compareType (ctx :< sArg) sRes.term tRes.term
compareType' ctx (Sig {fst = sFst, snd = sSnd, _})
(Sig {fst = tFst, snd = tSnd, _}) = do
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-- Γ ⊢ A₁ <: A₂ Γ, x : A₁ ⊢ B₁ <: B₂
-- --------------------------------------
-- Γ ⊢ (x : A₁) × B₁ <: (x : A₂) × B₂
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compareType ctx sFst tFst
compareType (ctx :< sFst) sSnd.term tSnd.term
compareType' ctx (Eq {ty = sTy, l = sl, r = sr, _})
(Eq {ty = tTy, l = tl, r = tr, _}) = do
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-- Γ ⊢ A₁ε/i <: A₂ε/i
-- Γ ⊢ l₁ = l₂ : A₁𝟎/i Γ ⊢ r₁ = r₂ : A₁𝟏/i
-- ------------------------------------------------
-- Γ ⊢ Eq [i ⇒ A₁] l₁ r₂ <: Eq [i ⇒ A₂] l₂ r₂
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compareType ctx sTy.zero tTy.zero
compareType ctx sTy.one tTy.one
local {mode := Equal} $ do
Term.compare0 ctx sTy.zero sl tl
Term.compare0 ctx sTy.one sr tr
compareType' ctx (E e) (E f) = do
-- no fanciness needed here cos anything other than a neutral
-- has been inlined by whnf
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Elim.compare0 ctx e f
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||| performs the minimum work required to recompute the type of an elim.
|||
||| ⚠ **assumes the elim is already typechecked.** ⚠
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private covering
computeElimType : TContext q 0 n -> (e : Elim q 0 n) ->
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(0 ne : NotRedex defs e) ->
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m (Term q 0 n)
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computeElimType ctx (F x) _ = do
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defs <- lookupFree' defs x
pure $ defs.type.get
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computeElimType ctx (B i) _ = do
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pure $ ctx !! i
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computeElimType ctx (f :@ s) ne = do
(_, arg, res) <- expectPi defs !(computeElimType ctx f (noOr1 ne))
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pure $ sub1 res (s :# arg)
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computeElimType ctx (CasePair {pair, ret, _}) _ = do
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pure $ sub1 ret pair
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computeElimType ctx (f :% p) ne = do
(ty, _, _) <- expectEq defs !(computeElimType ctx f (noOr1 ne))
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pure $ dsub1 ty p
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computeElimType ctx (_ :# ty) _ = do
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pure ty
private covering
replaceEnd : TContext q 0 n ->
(e : Elim q 0 n) -> DimConst -> (0 ne : NotRedex defs e) ->
m (Elim q 0 n)
replaceEnd ctx e p ne = do
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(ty, l, r) <- expectEq defs !(computeElimType ctx e ne)
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pure $ ends l r p :# dsub1 ty (K p)
namespace Elim
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-- [fixme] the following code ends up repeating a lot of work in the
-- computeElimType calls. the results should be shared better
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||| compare two eliminations according to the given variance `mode`.
|||
||| ⚠ **assumes that they have both been typechecked, and have
||| equal types.** ⚠
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export covering %inline
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compare0 : TContext q 0 n -> (e, f : Elim q 0 n) -> m ()
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compare0 ctx e f =
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wrapErr (WhileComparingE (MkTyContext new ctx) !mode e f) $ do
let Element e ne = whnf defs e
Element f nf = whnf defs f
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-- [fixme] there is a better way to do this "isSubSing" stuff for sure
unless (isSubSing defs !(computeElimType ctx e ne)) $
compare0' ctx e f ne nf
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private covering
compare0' : TContext q 0 n ->
(e, f : Elim q 0 n) ->
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(0 ne : NotRedex defs e) -> (0 nf : NotRedex defs f) ->
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m ()
-- replace applied equalities with the appropriate end first
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-- e.g. e : Eq [i ⇒ A] s t ⊢ e 𝟎 = s : A𝟎/i
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--
-- [todo] maybe have typed whnf and do this (and η???) there instead
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compare0' ctx (e :% K p) f ne nf =
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compare0 ctx !(replaceEnd ctx e p $ noOr1 ne) f
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compare0' ctx e (f :% K q) ne nf =
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compare0 ctx e !(replaceEnd ctx f q $ noOr1 nf)
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compare0' _ e@(F x) f@(F y) _ _ = unless (x == y) $ clashE e f
compare0' _ e@(F _) f _ _ = clashE e f
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compare0' ctx e@(B i) f@(B j) _ _ = unless (i == j) $ clashE e f
compare0' _ e@(B _) f _ _ = clashE e f
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compare0' ctx (e :@ s) (f :@ t) ne nf =
local {mode := Equal} $ do
compare0 ctx e f
(_, arg, _) <- expectPi defs !(computeElimType ctx e (noOr1 ne))
Term.compare0 ctx arg s t
compare0' _ e@(_ :@ _) f _ _ = clashE e f
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compare0' ctx (CasePair epi e _ eret _ _ ebody)
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(CasePair fpi f _ fret _ _ fbody) ne nf =
local {mode := Equal} $ do
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compare0 ctx e f
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ety <- computeElimType ctx e (noOr1 ne)
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compareType (ctx :< ety) eret.term fret.term
(fst, snd) <- expectSig defs ety
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Term.compare0 (ctx :< fst :< snd.term) (substCasePairRet ety eret)
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ebody.term fbody.term
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unless (epi == fpi) $ throwError $ ClashQ epi fpi
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compare0' _ e@(CasePair {}) f _ _ = clashE e f
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compare0' ctx (s :# a) (t :# _) _ _ = Term.compare0 ctx a s t
compare0' ctx (s :# a) f _ _ = Term.compare0 ctx a s (E f)
compare0' ctx e (t :# b) _ _ = Term.compare0 ctx b (E e) t
compare0' _ e@(_ :# _) f _ _ = clashE e f
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parameters {auto _ : (HasDefs' q _ m, HasErr q m, Eq q)} (ctx : TyContext q d n)
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parameters (mode : EqMode)
namespace Term
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export covering
compare : (ty, s, t : Term q d n) -> m ()
compare ty s t = do
defs <- ask
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runReaderT {m} (MkCmpContext {mode}) $
for_ (splits ctx.dctx) $ \th =>
compare0 defs (map (/// th) ctx.tctx)
(ty /// th) (s /// th) (t /// th)
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export covering
compareType : (s, t : Term q d n) -> m ()
compareType s t = do
defs <- ask
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runReaderT {m} (MkCmpContext {mode}) $
for_ (splits ctx.dctx) $ \th =>
compareType defs (map (/// th) ctx.tctx) (s /// th) (t /// th)
namespace Elim
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||| you don't have to pass the type in but the arguments must still be
||| of the same type!!
export covering %inline
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compare : (e, f : Elim q d n) -> m ()
compare e f = do
defs <- ask
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runReaderT {m} (MkCmpContext {mode}) $
for_ (splits ctx.dctx) $ \th =>
compare0 defs (map (/// th) ctx.tctx) (e /// th) (f /// th)
namespace Term
export covering %inline
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equal, sub, super : (ty, s, t : Term q d n) -> m ()
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equal = compare Equal
sub = compare Sub
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super = compare Super
export covering %inline
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equalType, subtype, supertype : (s, t : Term q d n) -> m ()
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equalType = compareType Equal
subtype = compareType Sub
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supertype = compareType Super
namespace Elim
export covering %inline
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equal, sub, super : (e, f : Elim q d n) -> m ()
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equal = compare Equal
sub = compare Sub
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super = compare Super