    -- | Type inference of @loop@.  This is complicated because of the
    -- uniqueness and size inference, so the implementation is separate
    -- from the main type checker.
    module Language.Futhark.TypeChecker.Terms.Loop
      ( UncheckedLoop,
        CheckedLoop,
        checkLoop,
      )
    where

    import Control.Monad
    import Control.Monad.Reader
    import Control.Monad.State
    import Data.Bifunctor
    import Data.Bitraversable
    import Data.List qualified as L
    import Data.Map.Strict qualified as M
    import Data.Maybe
    import Data.Set qualified as S
    import Futhark.Util (nubOrd)
    import Futhark.Util.Pretty hiding (group, space)
    import Language.Futhark
    import Language.Futhark.TypeChecker.Monad hiding (BoundV)
    import Language.Futhark.TypeChecker.Terms.Monad
    import Language.Futhark.TypeChecker.Terms.Pat
    import Language.Futhark.TypeChecker.Types
    import Language.Futhark.TypeChecker.Unify
    import Prelude hiding (mod)

    -- | Retrieve an oracle that can be used to decide whether two are in
    -- the same equivalence class (i.e. have been unified).  This is an
    -- exotic operation.
    getAreSame :: (MonadUnify m) => m (VName -> VName -> Bool)
    getAreSame :: forall (m :: * -> *). MonadUnify m => m (VName -> VName -> Bool)
    getAreSame = Map VName (Level, Constraint) -> VName -> VName -> Bool
    forall {a}. Map VName (a, Constraint) -> VName -> VName -> Bool
    check (Map VName (Level, Constraint) -> VName -> VName -> Bool)
    -> m (Map VName (Level, Constraint)) -> m (VName -> VName -> Bool)
    forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
    <$> m (Map VName (Level, Constraint))
    forall (m :: * -> *).
    MonadUnify m =>
    m (Map VName (Level, Constraint))
    getConstraints
      where
        check :: Map VName (a, Constraint) -> VName -> VName -> Bool
    check Map VName (a, Constraint)
    constraints VName
    x VName
    y =
          case (VName -> Map VName (a, Constraint) -> Maybe (a, Constraint)
    forall k a. Ord k => k -> Map k a -> Maybe a
    M.lookup VName
    x Map VName (a, Constraint)
    constraints, VName -> Map VName (a, Constraint) -> Maybe (a, Constraint)
    forall k a. Ord k => k -> Map k a -> Maybe a
    M.lookup VName
    y Map VName (a, Constraint)
    constraints) of
            (Just (a
    _, Size (Just (Var QualName VName
    x' Info StructType
    _ SrcLoc
    _)) Usage
    _), Maybe (a, Constraint)
    _) ->
              Map VName (a, Constraint) -> VName -> VName -> Bool
    check Map VName (a, Constraint)
    constraints (QualName VName -> VName
    forall vn. QualName vn -> vn
    qualLeaf QualName VName
    x') VName
    y
            (Maybe (a, Constraint)
    _, Just (a
    _, Size (Just (Var QualName VName
    y' Info StructType
    _ SrcLoc
    _)) Usage
    _)) ->
              Map VName (a, Constraint) -> VName -> VName -> Bool
    check Map VName (a, Constraint)
    constraints VName
    x (QualName VName -> VName
    forall vn. QualName vn -> vn
    qualLeaf QualName VName
    y')
            (Maybe (a, Constraint), Maybe (a, Constraint))
    _ ->
              VName
    x VName -> VName -> Bool
    forall a. Eq a => a -> a -> Bool
    == VName
    y

    -- | Replace specified sizes with distinct fresh size variables.
    someDimsFreshInType ::
      SrcLoc ->
      Name ->
      [VName] ->
      TypeBase Size als ->
      TermTypeM (TypeBase Size als)
    someDimsFreshInType :: forall als.
    SrcLoc
    -> Name
    -> [VName]
    -> TypeBase Exp als
    -> TermTypeM (TypeBase Exp als)
    someDimsFreshInType SrcLoc
    loc Name
    desc [VName]
    fresh TypeBase Exp als
    t = do
      areSameSize <- TermTypeM (VName -> VName -> Bool)
    forall (m :: * -> *). MonadUnify m => m (VName -> VName -> Bool)
    getAreSame
      let freshen VName
    v = (VName -> Bool) -> [VName] -> Bool
    forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
    any (VName -> VName -> Bool
    areSameSize VName
    v) [VName]
    fresh
      bitraverse (onDim freshen) pure t
      where
        onDim :: (VName -> Bool) -> Exp -> m Exp
    onDim VName -> Bool
    freshen (Var QualName VName
    d Info StructType
    _ SrcLoc
    _)
          | VName -> Bool
    freshen (VName -> Bool) -> VName -> Bool
    forall a b. (a -> b) -> a -> b
    $ QualName VName -> VName
    forall vn. QualName vn -> vn
    qualLeaf QualName VName
    d = do
              v <- Usage -> Name -> m VName
    forall (m :: * -> *). MonadUnify m => Usage -> Name -> m VName
    newFlexibleDim (SrcLoc -> Usage
    forall a. Located a => a -> Usage
    mkUsage' SrcLoc
    loc) Name
    desc
              pure $ sizeFromName (qualName v) loc
        onDim VName -> Bool
    _ Exp
    d = Exp -> m Exp
    forall a. a -> m a
    forall (f :: * -> *) a. Applicative f => a -> f a
    pure Exp
    d

    -- | Replace the specified sizes with fresh size variables of the
    -- specified ridigity.  Returns the new fresh size variables.
    freshDimsInType ::
      Usage ->
      Rigidity ->
      Name ->
      [VName] ->
      TypeBase Size u ->
      TermTypeM (TypeBase Size u, [VName])
    freshDimsInType :: forall u.
    Usage
    -> Rigidity
    -> Name
    -> [VName]
    -> TypeBase Exp u
    -> TermTypeM (TypeBase Exp u, [VName])
    freshDimsInType Usage
    usage Rigidity
    r Name
    desc [VName]
    fresh TypeBase Exp u
    t = do
      areSameSize <- TermTypeM (VName -> VName -> Bool)
    forall (m :: * -> *). MonadUnify m => m (VName -> VName -> Bool)
    getAreSame
      second (map snd) <$> runStateT (bitraverse (onDim areSameSize) pure t) mempty
      where
        onDim :: (VName -> VName -> Bool) -> Exp -> t m Exp
    onDim VName -> VName -> Bool
    areSameSize (Var (QualName [VName]
    _ VName
    d) Info StructType
    _ SrcLoc
    _)
          | (VName -> Bool) -> [VName] -> Bool
    forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Bool
    any (VName -> VName -> Bool
    areSameSize VName
    d) [VName]
    fresh = do
              prev_subst <- ([(VName, VName)] -> Maybe (VName, VName))
    -> t m (Maybe (VName, VName))
    forall s (m :: * -> *) a. MonadState s m => (s -> a) -> m a
    gets (([(VName, VName)] -> Maybe (VName, VName))
     -> t m (Maybe (VName, VName)))
    -> ([(VName, VName)] -> Maybe (VName, VName))
    -> t m (Maybe (VName, VName))
    forall a b. (a -> b) -> a -> b
    $ ((VName, VName) -> Bool)
    -> [(VName, VName)] -> Maybe (VName, VName)
    forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Maybe a
    L.find (VName -> VName -> Bool
    areSameSize VName
    d (VName -> Bool)
    -> ((VName, VName) -> VName) -> (VName, VName) -> Bool
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . (VName, VName) -> VName
    forall a b. (a, b) -> a
    fst)
              case prev_subst of
                Just (VName
    _, VName
    d') -> Exp -> t m Exp
    forall a. a -> t m a
    forall (f :: * -> *) a. Applicative f => a -> f a
    pure (Exp -> t m Exp) -> Exp -> t m Exp
    forall a b. (a -> b) -> a -> b
    $ QualName VName -> SrcLoc -> Exp
    sizeFromName (VName -> QualName VName
    forall v. v -> QualName v
    qualName VName
    d') (SrcLoc -> Exp) -> SrcLoc -> Exp
    forall a b. (a -> b) -> a -> b
    $ Usage -> SrcLoc
    forall a. Located a => a -> SrcLoc
    srclocOf Usage
    usage
                Maybe (VName, VName)
    Nothing -> do
                  v <- m VName -> t m VName
    forall (m :: * -> *) a. Monad m => m a -> t m a
    forall (t :: (* -> *) -> * -> *) (m :: * -> *) a.
    (MonadTrans t, Monad m) =>
    m a -> t m a
    lift (m VName -> t m VName) -> m VName -> t m VName
    forall a b. (a -> b) -> a -> b
    $ Usage -> Rigidity -> Name -> m VName
    forall (m :: * -> *).
    MonadUnify m =>
    Usage -> Rigidity -> Name -> m VName
    newDimVar Usage
    usage Rigidity
    r Name
    desc
                  modify ((d, v) :)
                  pure $ sizeFromName (qualName v) $ srclocOf usage
        onDim VName -> VName -> Bool
    _ Exp
    d = Exp -> t m Exp
    forall a. a -> t m a
    forall (f :: * -> *) a. Applicative f => a -> f a
    pure Exp
    d

    data ArgSource = Initial | BodyResult

    wellTypedLoopArg :: ArgSource -> [VName] -> Pat ParamType -> Exp -> TermTypeM ()
    wellTypedLoopArg :: ArgSource -> [VName] -> Pat ParamType -> Exp -> TermTypeM ()
    wellTypedLoopArg ArgSource
    src [VName]
    sparams Pat ParamType
    pat Exp
    arg = do
      (merge_t, _) <-
        Usage
    -> Rigidity
    -> Name
    -> [VName]
    -> StructType
    -> TermTypeM (StructType, [VName])
    forall u.
    Usage
    -> Rigidity
    -> Name
    -> [VName]
    -> TypeBase Exp u
    -> TermTypeM (TypeBase Exp u, [VName])
    freshDimsInType (Exp -> Text -> Usage
    forall a. Located a => a -> Text -> Usage
    mkUsage Exp
    arg Text
    desc) Rigidity
    Nonrigid Name
    "loop" [VName]
    sparams (StructType -> TermTypeM (StructType, [VName]))
    -> StructType -> TermTypeM (StructType, [VName])
    forall a b. (a -> b) -> a -> b
    $
          ParamType -> StructType
    forall dim u. TypeBase dim u -> TypeBase dim NoUniqueness
    toStruct (Pat ParamType -> ParamType
    forall d u. Pat (TypeBase d u) -> TypeBase d u
    patternType Pat ParamType
    pat)
      arg_t <- toStruct <$> expTypeFully arg
      onFailure (checking merge_t arg_t) $
        unify (mkUsage arg desc) merge_t arg_t
      where
        (StructType -> StructType -> Checking
    checking, Text
    desc) =
          case ArgSource
    src of
            ArgSource
    Initial -> (StructType -> StructType -> Checking
    CheckingLoopInitial, Text
    "matching initial loop values to pattern")
            ArgSource
    BodyResult -> (StructType -> StructType -> Checking
    CheckingLoopBody, Text
    "matching loop body to pattern")

    -- | An un-checked loop.
    type UncheckedLoop =
      (PatBase NoInfo VName ParamType, LoopInitBase NoInfo VName, LoopFormBase NoInfo VName, ExpBase NoInfo VName)

    -- | A loop that has been type-checked.
    type CheckedLoop =
      ([VName], Pat ParamType, LoopInitBase Info VName, LoopFormBase Info VName, Exp)

    checkForImpossible :: Loc -> S.Set VName -> ParamType -> TermTypeM ()
    checkForImpossible :: Loc -> Set VName -> ParamType -> TermTypeM ()
    checkForImpossible Loc
    loc Set VName
    known_before ParamType
    pat_t = do
      cs <- TermTypeM (Map VName (Level, Constraint))
    forall (m :: * -> *).
    MonadUnify m =>
    m (Map VName (Level, Constraint))
    getConstraints
      let bad VName
    v = do
            Bool -> Maybe ()
    forall (f :: * -> *). Alternative f => Bool -> f ()
    guard (Bool -> Maybe ()) -> Bool -> Maybe ()
    forall a b. (a -> b) -> a -> b
    $ VName
    v VName -> Set VName -> Bool
    forall a. Ord a => a -> Set a -> Bool
    `S.notMember` Set VName
    known_before
            (_, UnknownSize v_loc _) <- VName -> Map VName (Level, Constraint) -> Maybe (Level, Constraint)
    forall k a. Ord k => k -> Map k a -> Maybe a
    M.lookup VName
    v Map VName (Level, Constraint)
    cs
            Just . typeError (srclocOf loc) mempty $
              "Inferred type for loop parameter is"
                </> indent 2 (pretty pat_t)
                </> "but"
                <+> dquotes (prettyName v)
                <+> "is an existential size created inside the loop body at"
                <+> pretty (locStrRel loc v_loc)
                <> "."
      case mapMaybe bad $ S.toList $ fvVars $ freeInType pat_t of
        TermTypeM ()
    problem : [TermTypeM ()]
    _ -> TermTypeM ()
    problem
        [] -> () -> TermTypeM ()
    forall a. a -> TermTypeM a
    forall (f :: * -> *) a. Applicative f => a -> f a
    pure ()

    -- | Type-check a @loop@ expression, passing in a function for
    -- type-checking subexpressions.
    checkLoop ::
      (ExpBase NoInfo VName -> TermTypeM Exp) ->
      UncheckedLoop ->
      SrcLoc ->
      TermTypeM (CheckedLoop, AppRes)
    checkLoop :: (ExpBase NoInfo VName -> TermTypeM Exp)
    -> UncheckedLoop -> SrcLoc -> TermTypeM (CheckedLoop, AppRes)
    checkLoop ExpBase NoInfo VName -> TermTypeM Exp
    checkExp (PatBase NoInfo VName ParamType
    mergepat, LoopInitBase NoInfo VName
    loopinit, LoopFormBase NoInfo VName
    form, ExpBase NoInfo VName
    loopbody) SrcLoc
    loc = do
      loopinit' <- ExpBase NoInfo VName -> TermTypeM Exp
    checkExp (ExpBase NoInfo VName -> TermTypeM Exp)
    -> ExpBase NoInfo VName -> TermTypeM Exp
    forall a b. (a -> b) -> a -> b
    $ case LoopInitBase NoInfo VName
    loopinit of
        LoopInitExplicit ExpBase NoInfo VName
    e -> ExpBase NoInfo VName
    e
        LoopInitImplicit NoInfo (ExpBase NoInfo VName)
    _ ->
          -- Should have been filled out in Names
          String -> ExpBase NoInfo VName
    forall a. HasCallStack => String -> a
    error String
    "Unspected LoopInitImplicit"
      known_before <- M.keysSet <$> getConstraints
      zeroOrderType
        (mkUsage loopinit' "use as loop variable")
        "type used as loop variable"
        . toStruct
        =<< expTypeFully loopinit'

      -- The handling of dimension sizes is a bit intricate, but very
      -- similar to checking a function, followed by checking a call to
      -- it.  The overall procedure is as follows:
      --
      -- (1) All empty dimensions in the merge pattern are instantiated
      -- with nonrigid size variables.  All explicitly specified
      -- dimensions are preserved.
      --
      -- (2) The body of the loop is type-checked.  The result type is
      -- combined with the merge pattern type to determine which sizes are
      -- variant, and these are turned into size parameters for the merge
      -- pattern.
      --
      -- (3) We now conceptually have a function parameter type and
      -- return type.  We check that it can be called with the body type
      -- as argument.
      --
      -- (4) Similarly to (3), we check that the "function" can be
      -- called with the initial merge values as argument.  The result
      -- of this is the type of the loop as a whole.

      (merge_t, new_dims_map) <-
        -- dim handling (1)
        allDimsFreshInType (mkUsage loc "loop parameter type inference") Nonrigid "loop_d"
          =<< expTypeFully loopinit'
      let new_dims_to_initial_dim = Map VName Exp -> [(VName, Exp)]
    forall k a. Map k a -> [(k, a)]
    M.toList Map VName Exp
    new_dims_map
          new_dims = ((VName, Exp) -> VName) -> [(VName, Exp)] -> [VName]
    forall a b. (a -> b) -> [a] -> [b]
    map (VName, Exp) -> VName
    forall a b. (a, b) -> a
    fst [(VName, Exp)]
    new_dims_to_initial_dim

      -- dim handling (2)
      let checkLoopReturnSize Pat ParamType
    mergepat' Exp
    loopbody' = do
            loopbody_t <- Exp -> TermTypeM StructType
    expTypeFully Exp
    loopbody'
            mergepat_t <- normTypeFully (patternType mergepat')

            let ok_names = Set VName
    known_before Set VName -> Set VName -> Set VName
    forall a. Semigroup a => a -> a -> a
    <> [VName] -> Set VName
    forall a. Ord a => [a] -> Set a
    S.fromList [VName]
    new_dims
            checkForImpossible (locOf mergepat) ok_names mergepat_t

            pat_t <- someDimsFreshInType loc "loop" new_dims mergepat_t

            -- We are ignoring the dimensions here, because any mismatches
            -- should be turned into fresh size variables.
            onFailure (CheckingLoopBody (toStruct pat_t) (toStruct loopbody_t)) $
              unify
                (mkUsage loopbody "matching loop body to loop pattern")
                (toStruct pat_t)
                (toStruct loopbody_t)

            -- Figure out which of the 'new_dims' dimensions are variant.
            -- This works because we know that each dimension from
            -- new_dims in the pattern is unique and distinct.
            areSameSize <- getAreSame
            let onDims p
    _ Exp
    x Exp
    y
                  | Exp
    x Exp -> Exp -> Bool
    forall a. Eq a => a -> a -> Bool
    == Exp
    y = Exp -> f Exp
    forall a. a -> f a
    forall (f :: * -> *) a. Applicative f => a -> f a
    pure Exp
    x
                onDims p
    _ Exp
    e Exp
    d = do
                  Set VName -> (VName -> f ()) -> f ()
    forall (t :: * -> *) (m :: * -> *) a b.
    (Foldable t, Monad m) =>
    t a -> (a -> m b) -> m ()
    forM_ (FV -> Set VName
    fvVars (FV -> Set VName) -> FV -> Set VName
    forall a b. (a -> b) -> a -> b
    $ Exp -> FV
    freeInExp Exp
    e) ((VName -> f ()) -> f ()) -> (VName -> f ()) -> f ()
    forall a b. (a -> b) -> a -> b
    $ \VName
    v -> do
                    case ((VName, Exp) -> Bool) -> [(VName, Exp)] -> Maybe (VName, Exp)
    forall (t :: * -> *) a. Foldable t => (a -> Bool) -> t a -> Maybe a
    L.find (VName -> VName -> Bool
    areSameSize VName
    v (VName -> Bool) -> ((VName, Exp) -> VName) -> (VName, Exp) -> Bool
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . (VName, Exp) -> VName
    forall a b. (a, b) -> a
    fst) [(VName, Exp)]
    new_dims_to_initial_dim of
                      Just (VName
    _, Exp
    e') ->
                        if Exp
    e' Exp -> Exp -> Bool
    forall a. Eq a => a -> a -> Bool
    == Exp
    d
                          then (p (Map VName (Subst t)) [VName]
     -> p (Map VName (Subst t)) [VName])
    -> f ()
    forall s (m :: * -> *). MonadState s m => (s -> s) -> m ()
    modify ((p (Map VName (Subst t)) [VName]
      -> p (Map VName (Subst t)) [VName])
     -> f ())
    -> (p (Map VName (Subst t)) [VName]
        -> p (Map VName (Subst t)) [VName])
    -> f ()
    forall a b. (a -> b) -> a -> b
    $ (Map VName (Subst t) -> Map VName (Subst t))
    -> p (Map VName (Subst t)) [VName]
    -> p (Map VName (Subst t)) [VName]
    forall a b c. (a -> b) -> p a c -> p b c
    forall (p :: * -> * -> *) a b c.
    Bifunctor p =>
    (a -> b) -> p a c -> p b c
    first ((Map VName (Subst t) -> Map VName (Subst t))
     -> p (Map VName (Subst t)) [VName]
     -> p (Map VName (Subst t)) [VName])
    -> (Map VName (Subst t) -> Map VName (Subst t))
    -> p (Map VName (Subst t)) [VName]
    -> p (Map VName (Subst t)) [VName]
    forall a b. (a -> b) -> a -> b
    $ VName -> Subst t -> Map VName (Subst t) -> Map VName (Subst t)
    forall k a. Ord k => k -> a -> Map k a -> Map k a
    M.insert VName
    v (Subst t -> Map VName (Subst t) -> Map VName (Subst t))
    -> Subst t -> Map VName (Subst t) -> Map VName (Subst t)
    forall a b. (a -> b) -> a -> b
    $ Exp -> Subst t
    forall t. Exp -> Subst t
    ExpSubst Exp
    e'
                          else
                            Bool -> f () -> f ()
    forall (f :: * -> *). Applicative f => Bool -> f () -> f ()
    unless (VName
    v VName -> Set VName -> Bool
    forall a. Ord a => a -> Set a -> Bool
    `S.member` Set VName
    known_before) (f () -> f ()) -> f () -> f ()
    forall a b. (a -> b) -> a -> b
    $
                              (p (Map VName (Subst t)) [VName]
     -> p (Map VName (Subst t)) [VName])
    -> f ()
    forall s (m :: * -> *). MonadState s m => (s -> s) -> m ()
    modify (([VName] -> [VName])
    -> p (Map VName (Subst t)) [VName]
    -> p (Map VName (Subst t)) [VName]
    forall b c a. (b -> c) -> p a b -> p a c
    forall (p :: * -> * -> *) b c a.
    Bifunctor p =>
    (b -> c) -> p a b -> p a c
    second (VName
    v VName -> [VName] -> [VName]
    forall a. a -> [a] -> [a]
    :))
                      Maybe (VName, Exp)
    _ ->
                        () -> f ()
    forall a. a -> f a
    forall (f :: * -> *) a. Applicative f => a -> f a
    pure ()
                  Exp -> f Exp
    forall a. a -> f a
    forall (f :: * -> *) a. Applicative f => a -> f a
    pure Exp
    e
            loopbody_t' <- normTypeFully loopbody_t
            merge_t' <- normTypeFully merge_t

            let (init_substs, sparams) =
                  execState (matchDims onDims merge_t' loopbody_t') mempty

            -- Make sure that any of new_dims that are invariant will be
            -- replaced with the invariant size in the loop body.  Failure
            -- to do this can cause type annotations to still refer to
            -- new_dims.
            let dimToInit (VName
    v, ExpSubst Exp
    e) =
                  VName -> Constraint -> TermTypeM ()
    constrain VName
    v (Constraint -> TermTypeM ()) -> Constraint -> TermTypeM ()
    forall a b. (a -> b) -> a -> b
    $ Maybe Exp -> Usage -> Constraint
    Size (Exp -> Maybe Exp
    forall a. a -> Maybe a
    Just Exp
    e) (SrcLoc -> Text -> Usage
    forall a. Located a => a -> Text -> Usage
    mkUsage SrcLoc
    loc Text
    "size of loop parameter")
                dimToInit (VName, Subst t)
    _ =
                  () -> TermTypeM ()
    forall a. a -> TermTypeM a
    forall (f :: * -> *) a. Applicative f => a -> f a
    pure ()
            mapM_ dimToInit $ M.toList init_substs

            mergepat'' <- applySubst (`M.lookup` init_substs) <$> updateTypes mergepat'

            -- Eliminate those new_dims that turned into sparams so it won't
            -- look like we have ambiguous sizes lying around.
            modifyConstraints $ M.filterWithKey $ \VName
    k (Level, Constraint)
    _ -> VName
    k VName -> [VName] -> Bool
    forall (t :: * -> *) a. (Foldable t, Eq a) => a -> t a -> Bool
    `notElem` [VName]
    sparams

            -- dim handling (3)
            --
            -- The only trick here is that we have to turn any instances
            -- of loop parameters in the type of loopbody' rigid,
            -- because we are no longer in a position to change them,
            -- really.
            wellTypedLoopArg BodyResult sparams mergepat'' loopbody'

            pure (nubOrd sparams, mergepat'')

      (sparams, mergepat', form', loopbody') <-
        case form of
          For IdentBase NoInfo VName StructType
    i ExpBase NoInfo VName
    uboundexp -> do
            uboundexp' <-
              Text -> [PrimType] -> Exp -> TermTypeM Exp
    require Text
    "being the bound in a 'for' loop" [PrimType]
    anySignedType
                (Exp -> TermTypeM Exp) -> TermTypeM Exp -> TermTypeM Exp
    forall (m :: * -> *) a b. Monad m => (a -> m b) -> m a -> m b
    =<< ExpBase NoInfo VName -> TermTypeM Exp
    checkExp ExpBase NoInfo VName
    uboundexp
            bound_t <- expTypeFully uboundexp'
            bindingIdent i bound_t $ \Ident StructType
    i' ->
              [SizeBinder VName]
    -> PatBase NoInfo VName ParamType
    -> StructType
    -> (Pat ParamType
        -> TermTypeM
             ([VName], Pat ParamType, LoopFormBase Info VName, Exp))
    -> TermTypeM ([VName], Pat ParamType, LoopFormBase Info VName, Exp)
    forall u a.
    [SizeBinder VName]
    -> PatBase NoInfo VName (TypeBase Exp u)
    -> StructType
    -> (Pat ParamType -> TermTypeM a)
    -> TermTypeM a
    bindingPat [] PatBase NoInfo VName ParamType
    mergepat StructType
    merge_t ((Pat ParamType
      -> TermTypeM
           ([VName], Pat ParamType, LoopFormBase Info VName, Exp))
     -> TermTypeM
          ([VName], Pat ParamType, LoopFormBase Info VName, Exp))
    -> (Pat ParamType
        -> TermTypeM
             ([VName], Pat ParamType, LoopFormBase Info VName, Exp))
    -> TermTypeM ([VName], Pat ParamType, LoopFormBase Info VName, Exp)
    forall a b. (a -> b) -> a -> b
    $ \Pat ParamType
    mergepat' -> TermTypeM ([VName], Pat ParamType, LoopFormBase Info VName, Exp)
    -> TermTypeM ([VName], Pat ParamType, LoopFormBase Info VName, Exp)
    forall a. TermTypeM a -> TermTypeM a
    incLevel (TermTypeM ([VName], Pat ParamType, LoopFormBase Info VName, Exp)
     -> TermTypeM
          ([VName], Pat ParamType, LoopFormBase Info VName, Exp))
    -> TermTypeM ([VName], Pat ParamType, LoopFormBase Info VName, Exp)
    -> TermTypeM ([VName], Pat ParamType, LoopFormBase Info VName, Exp)
    forall a b. (a -> b) -> a -> b
    $ do
                loopbody' <- ExpBase NoInfo VName -> TermTypeM Exp
    checkExp ExpBase NoInfo VName
    loopbody
                (sparams, mergepat'') <- checkLoopReturnSize mergepat' loopbody'
                pure
                  ( sparams,
                    mergepat'',
                    For i' uboundexp',
                    loopbody'
                  )
          ForIn PatBase NoInfo VName StructType
    xpat ExpBase NoInfo VName
    e -> do
            (arr_t, _) <- Usage -> Name -> Level -> TermTypeM (StructType, StructType)
    newArrayType (SrcLoc -> Usage
    forall a. Located a => a -> Usage
    mkUsage' (ExpBase NoInfo VName -> SrcLoc
    forall a. Located a => a -> SrcLoc
    srclocOf ExpBase NoInfo VName
    e)) Name
    "e" Level
    1
            e' <- unifies "being iterated in a 'for-in' loop" arr_t =<< checkExp e
            t <- expTypeFully e'
            case t of
              StructType
    _
                | Just StructType
    t' <- Level -> StructType -> Maybe StructType
    forall dim u. Level -> TypeBase dim u -> Maybe (TypeBase dim u)
    peelArray Level
    1 StructType
    t ->
                    [SizeBinder VName]
    -> PatBase NoInfo VName StructType
    -> StructType
    -> (Pat ParamType
        -> TermTypeM
             ([VName], Pat ParamType, LoopFormBase Info VName, Exp))
    -> TermTypeM ([VName], Pat ParamType, LoopFormBase Info VName, Exp)
    forall u a.
    [SizeBinder VName]
    -> PatBase NoInfo VName (TypeBase Exp u)
    -> StructType
    -> (Pat ParamType -> TermTypeM a)
    -> TermTypeM a
    bindingPat [] PatBase NoInfo VName StructType
    xpat StructType
    t' ((Pat ParamType
      -> TermTypeM
           ([VName], Pat ParamType, LoopFormBase Info VName, Exp))
     -> TermTypeM
          ([VName], Pat ParamType, LoopFormBase Info VName, Exp))
    -> (Pat ParamType
        -> TermTypeM
             ([VName], Pat ParamType, LoopFormBase Info VName, Exp))
    -> TermTypeM ([VName], Pat ParamType, LoopFormBase Info VName, Exp)
    forall a b. (a -> b) -> a -> b
    $ \Pat ParamType
    xpat' ->
                      [SizeBinder VName]
    -> PatBase NoInfo VName ParamType
    -> StructType
    -> (Pat ParamType
        -> TermTypeM
             ([VName], Pat ParamType, LoopFormBase Info VName, Exp))
    -> TermTypeM ([VName], Pat ParamType, LoopFormBase Info VName, Exp)
    forall u a.
    [SizeBinder VName]
    -> PatBase NoInfo VName (TypeBase Exp u)
    -> StructType
    -> (Pat ParamType -> TermTypeM a)
    -> TermTypeM a
    bindingPat [] PatBase NoInfo VName ParamType
    mergepat StructType
    merge_t ((Pat ParamType
      -> TermTypeM
           ([VName], Pat ParamType, LoopFormBase Info VName, Exp))
     -> TermTypeM
          ([VName], Pat ParamType, LoopFormBase Info VName, Exp))
    -> (Pat ParamType
        -> TermTypeM
             ([VName], Pat ParamType, LoopFormBase Info VName, Exp))
    -> TermTypeM ([VName], Pat ParamType, LoopFormBase Info VName, Exp)
    forall a b. (a -> b) -> a -> b
    $ \Pat ParamType
    mergepat' -> TermTypeM ([VName], Pat ParamType, LoopFormBase Info VName, Exp)
    -> TermTypeM ([VName], Pat ParamType, LoopFormBase Info VName, Exp)
    forall a. TermTypeM a -> TermTypeM a
    incLevel (TermTypeM ([VName], Pat ParamType, LoopFormBase Info VName, Exp)
     -> TermTypeM
          ([VName], Pat ParamType, LoopFormBase Info VName, Exp))
    -> TermTypeM ([VName], Pat ParamType, LoopFormBase Info VName, Exp)
    -> TermTypeM ([VName], Pat ParamType, LoopFormBase Info VName, Exp)
    forall a b. (a -> b) -> a -> b
    $ do
                        loopbody' <- ExpBase NoInfo VName -> TermTypeM Exp
    checkExp ExpBase NoInfo VName
    loopbody
                        (sparams, mergepat'') <- checkLoopReturnSize mergepat' loopbody'
                        pure
                          ( sparams,
                            mergepat'',
                            ForIn (fmap toStruct xpat') e',
                            loopbody'
                          )
                | Bool
    otherwise ->
                    SrcLoc
    -> Notes
    -> Doc ()
    -> TermTypeM ([VName], Pat ParamType, LoopFormBase Info VName, Exp)
    forall loc a. Located loc => loc -> Notes -> Doc () -> TermTypeM a
    forall (m :: * -> *) loc a.
    (MonadTypeChecker m, Located loc) =>
    loc -> Notes -> Doc () -> m a
    typeError (ExpBase NoInfo VName -> SrcLoc
    forall a. Located a => a -> SrcLoc
    srclocOf ExpBase NoInfo VName
    e) Notes
    forall a. Monoid a => a
    mempty (Doc ()
     -> TermTypeM
          ([VName], Pat ParamType, LoopFormBase Info VName, Exp))
    -> Doc ()
    -> TermTypeM ([VName], Pat ParamType, LoopFormBase Info VName, Exp)
    forall a b. (a -> b) -> a -> b
    $
                      Doc ()
    "Iteratee of a for-in loop must be an array, but expression has type"
                        Doc () -> Doc () -> Doc ()
    forall a. Doc a -> Doc a -> Doc a
    <+> StructType -> Doc ()
    forall a ann. Pretty a => a -> Doc ann
    forall ann. StructType -> Doc ann
    pretty StructType
    t
          While ExpBase NoInfo VName
    cond ->
            [SizeBinder VName]
    -> PatBase NoInfo VName ParamType
    -> StructType
    -> (Pat ParamType
        -> TermTypeM
             ([VName], Pat ParamType, LoopFormBase Info VName, Exp))
    -> TermTypeM ([VName], Pat ParamType, LoopFormBase Info VName, Exp)
    forall u a.
    [SizeBinder VName]
    -> PatBase NoInfo VName (TypeBase Exp u)
    -> StructType
    -> (Pat ParamType -> TermTypeM a)
    -> TermTypeM a
    bindingPat [] PatBase NoInfo VName ParamType
    mergepat StructType
    merge_t ((Pat ParamType
      -> TermTypeM
           ([VName], Pat ParamType, LoopFormBase Info VName, Exp))
     -> TermTypeM
          ([VName], Pat ParamType, LoopFormBase Info VName, Exp))
    -> (Pat ParamType
        -> TermTypeM
             ([VName], Pat ParamType, LoopFormBase Info VName, Exp))
    -> TermTypeM ([VName], Pat ParamType, LoopFormBase Info VName, Exp)
    forall a b. (a -> b) -> a -> b
    $ \Pat ParamType
    mergepat' ->
              TermTypeM ([VName], Pat ParamType, LoopFormBase Info VName, Exp)
    -> TermTypeM ([VName], Pat ParamType, LoopFormBase Info VName, Exp)
    forall a. TermTypeM a -> TermTypeM a
    incLevel (TermTypeM ([VName], Pat ParamType, LoopFormBase Info VName, Exp)
     -> TermTypeM
          ([VName], Pat ParamType, LoopFormBase Info VName, Exp))
    -> TermTypeM ([VName], Pat ParamType, LoopFormBase Info VName, Exp)
    -> TermTypeM ([VName], Pat ParamType, LoopFormBase Info VName, Exp)
    forall a b. (a -> b) -> a -> b
    $ do
                cond' <-
                  ExpBase NoInfo VName -> TermTypeM Exp
    checkExp ExpBase NoInfo VName
    cond
                    TermTypeM Exp -> (Exp -> TermTypeM Exp) -> TermTypeM Exp
    forall a b. TermTypeM a -> (a -> TermTypeM b) -> TermTypeM b
    forall (m :: * -> *) a b. Monad m => m a -> (a -> m b) -> m b
    >>= Text -> StructType -> Exp -> TermTypeM Exp
    unifies Text
    "being the condition of a 'while' loop" (ScalarTypeBase Exp NoUniqueness -> StructType
    forall dim u. ScalarTypeBase dim u -> TypeBase dim u
    Scalar (ScalarTypeBase Exp NoUniqueness -> StructType)
    -> ScalarTypeBase Exp NoUniqueness -> StructType
    forall a b. (a -> b) -> a -> b
    $ PrimType -> ScalarTypeBase Exp NoUniqueness
    forall dim u. PrimType -> ScalarTypeBase dim u
    Prim PrimType
    Bool)
                loopbody' <- checkExp loopbody
                (sparams, mergepat'') <- checkLoopReturnSize mergepat' loopbody'
                pure
                  ( sparams,
                    mergepat'',
                    While cond',
                    loopbody'
                  )

      -- dim handling (4)
      wellTypedLoopArg Initial sparams mergepat' loopinit'

      (loopt, retext) <-
        freshDimsInType
          (mkUsage loc "inference of loop result type")
          (Rigid RigidLoop)
          "loop"
          sparams
          (patternType mergepat')
      pure
        ( (sparams, mergepat', LoopInitExplicit loopinit', form', loopbody'),
          AppRes (toStruct loopt) retext
        )