module Dhall.TypeCheck (
typeWith
, typeOf
, X(..)
, TypeError(..)
, DetailedTypeError(..)
, TypeMessage(..)
) where
import Control.Exception (Exception)
import Data.Foldable (forM_, toList)
import Data.Monoid ((<>))
import Data.Set (Set)
import Data.Text.Buildable (Buildable(..))
import Data.Text.Lazy (Text)
import Data.Text.Lazy.Builder (Builder)
import Data.Traversable (forM)
import Data.Typeable (Typeable)
import Dhall.Core (Const(..), Expr(..), Var(..))
import Dhall.Context (Context)
import qualified Control.Monad.Trans.State.Strict as State
import qualified Data.Map
import qualified Data.Set
import qualified Data.Text
import qualified Data.Text.Lazy as Text
import qualified Data.Text.Lazy.Builder as Builder
import qualified Data.Vector
import qualified Dhall.Context
import qualified Dhall.Core
import qualified NeatInterpolation
axiom :: Const -> Either (TypeError s) Const
axiom Type = return Kind
axiom Kind = Left (TypeError Dhall.Context.empty (Const Kind) Untyped)
rule :: Const -> Const -> Either () Const
rule Type Kind = Left ()
rule Type Type = return Type
rule Kind Kind = return Kind
rule Kind Type = return Type
match :: Var -> Var -> [(Text, Text)] -> Bool
match (V xL nL) (V xR nR) [] =
xL == xR && nL == nR
match (V xL 0 ) (V xR 0 ) ((xL', xR'):_ )
| xL == xL' && xR == xR' = True
match (V xL nL) (V xR nR) ((xL', xR'):xs) =
match (V xL nL') (V xR nR') xs
where
nL' = if xL == xL' then nL 1 else nL
nR' = if xR == xR' then nR 1 else nR
propEqual :: Expr s X -> Expr t X -> Bool
propEqual eL0 eR0 =
State.evalState
(go (Dhall.Core.normalize eL0) (Dhall.Core.normalize eR0))
[]
where
go (Const Type) (Const Type) = return True
go (Const Kind) (Const Kind) = return True
go (Var vL) (Var vR) = do
ctx <- State.get
return (match vL vR ctx)
go (Pi xL tL bL) (Pi xR tR bR) = do
ctx <- State.get
eq1 <- go tL tR
if eq1
then do
State.put ((xL, xR):ctx)
eq2 <- go bL bR
State.put ctx
return eq2
else return False
go (App fL aL) (App fR aR) = do
b1 <- go fL fR
if b1 then go aL aR else return False
go Bool Bool = return True
go Natural Natural = return True
go Integer Integer = return True
go Double Double = return True
go Text Text = return True
go List List = return True
go Optional Optional = return True
go (Record ktsL0) (Record ktsR0) = do
let loop ((kL, tL):ktsL) ((kR, tR):ktsR)
| kL == kR = do
b <- go tL tR
if b
then loop ktsL ktsR
else return False
loop [] [] = return True
loop _ _ = return False
loop (Data.Map.toList ktsL0) (Data.Map.toList ktsR0)
go (Union ktsL0) (Union ktsR0) = do
let loop ((kL, tL):ktsL) ((kR, tR):ktsR)
| kL == kR = do
b <- go tL tR
if b
then loop ktsL ktsR
else return False
loop [] [] = return True
loop _ _ = return False
loop (Data.Map.toList ktsL0) (Data.Map.toList ktsR0)
go _ _ = return False
typeWith :: Context (Expr s X) -> Expr s X -> Either (TypeError s) (Expr s X)
typeWith _ (Const c ) = do
fmap Const (axiom c)
typeWith ctx e@(Var (V x n) ) = do
case Dhall.Context.lookup x n ctx of
Nothing -> Left (TypeError ctx e UnboundVariable)
Just a -> return a
typeWith ctx (Lam x _A b ) = do
let ctx' = fmap (Dhall.Core.shift 1 (V x 0)) (Dhall.Context.insert x _A ctx)
_B <- typeWith ctx' b
let p = Pi x _A _B
_t <- typeWith ctx p
return p
typeWith ctx e@(Pi x _A _B ) = do
tA <- fmap Dhall.Core.normalize (typeWith ctx _A)
kA <- case tA of
Const k -> return k
_ -> Left (TypeError ctx e (InvalidInputType _A))
let ctx' = fmap (Dhall.Core.shift 1 (V x 0)) (Dhall.Context.insert x _A ctx)
tB <- fmap Dhall.Core.normalize (typeWith ctx' _B)
kB <- case tB of
Const k -> return k
_ -> Left (TypeError ctx' e (InvalidOutputType _B))
case rule kA kB of
Left () -> Left (TypeError ctx e (NoDependentTypes _A _B))
Right k -> Right (Const k)
typeWith ctx e@(App f a ) = do
tf <- fmap Dhall.Core.normalize (typeWith ctx f)
(x, _A, _B) <- case tf of
Pi x _A _B -> return (x, _A, _B)
_ -> Left (TypeError ctx e (NotAFunction f tf))
_A' <- typeWith ctx a
if propEqual _A _A'
then do
let a' = Dhall.Core.shift 1 (V x 0) a
let _B' = Dhall.Core.subst (V x 0) a' _B
let _B'' = Dhall.Core.shift (1) (V x 0) _B'
return _B''
else do
let nf_A = Dhall.Core.normalize _A
let nf_A' = Dhall.Core.normalize _A'
Left (TypeError ctx e (TypeMismatch f nf_A a nf_A'))
typeWith ctx e@(Let f mt r b ) = do
tR <- typeWith ctx r
ttR <- fmap Dhall.Core.normalize (typeWith ctx tR)
kR <- case ttR of
Const k -> return k
_ -> Left (TypeError ctx e (InvalidInputType tR))
let ctx' = Dhall.Context.insert f tR ctx
tB <- typeWith ctx' b
ttB <- fmap Dhall.Core.normalize (typeWith ctx tB)
kB <- case ttB of
Const k -> return k
_ -> Left (TypeError ctx e (InvalidOutputType tB))
case rule kR kB of
Left () -> Left (TypeError ctx e (NoDependentLet tR tB))
Right _ -> return ()
case mt of
Nothing -> do
return ()
Just t -> do
let nf_t = Dhall.Core.normalize t
let nf_tR = Dhall.Core.normalize tR
if propEqual nf_tR nf_t
then return ()
else Left (TypeError ctx e (AnnotMismatch r nf_t nf_tR))
return tB
typeWith ctx e@(Annot x t ) = do
_ <- typeWith ctx t
t' <- typeWith ctx x
if propEqual t t'
then do
return t
else do
let nf_t = Dhall.Core.normalize t
let nf_t' = Dhall.Core.normalize t'
Left (TypeError ctx e (AnnotMismatch x nf_t nf_t'))
typeWith _ Bool = do
return (Const Type)
typeWith _ (BoolLit _ ) = do
return Bool
typeWith ctx e@(BoolAnd l r ) = do
tl <- fmap Dhall.Core.normalize (typeWith ctx l)
case tl of
Bool -> return ()
_ -> Left (TypeError ctx e (CantAnd l tl))
tr <- fmap Dhall.Core.normalize (typeWith ctx r)
case tr of
Bool -> return ()
_ -> Left (TypeError ctx e (CantAnd r tr))
return Bool
typeWith ctx e@(BoolOr l r ) = do
tl <- fmap Dhall.Core.normalize (typeWith ctx l)
case tl of
Bool -> return ()
_ -> Left (TypeError ctx e (CantOr l tl))
tr <- fmap Dhall.Core.normalize (typeWith ctx r)
case tr of
Bool -> return ()
_ -> Left (TypeError ctx e (CantOr r tr))
return Bool
typeWith ctx e@(BoolEQ l r ) = do
tl <- fmap Dhall.Core.normalize (typeWith ctx l)
case tl of
Bool -> return ()
_ -> Left (TypeError ctx e (CantEQ l tl))
tr <- fmap Dhall.Core.normalize (typeWith ctx r)
case tr of
Bool -> return ()
_ -> Left (TypeError ctx e (CantEQ r tr))
return Bool
typeWith ctx e@(BoolNE l r ) = do
tl <- fmap Dhall.Core.normalize (typeWith ctx l)
case tl of
Bool -> return ()
_ -> Left (TypeError ctx e (CantNE l tl))
tr <- fmap Dhall.Core.normalize (typeWith ctx r)
case tr of
Bool -> return ()
_ -> Left (TypeError ctx e (CantNE r tr))
return Bool
typeWith ctx e@(BoolIf x y z ) = do
tx <- fmap Dhall.Core.normalize (typeWith ctx x)
case tx of
Bool -> return ()
_ -> Left (TypeError ctx e (InvalidPredicate x tx))
ty <- fmap Dhall.Core.normalize (typeWith ctx y )
tty <- fmap Dhall.Core.normalize (typeWith ctx ty)
case tty of
Const Type -> return ()
_ -> Left (TypeError ctx e (IfBranchMustBeTerm True y ty tty))
tz <- fmap Dhall.Core.normalize (typeWith ctx z)
ttz <- fmap Dhall.Core.normalize (typeWith ctx tz)
case ttz of
Const Type -> return ()
_ -> Left (TypeError ctx e (IfBranchMustBeTerm False z tz ttz))
if propEqual ty tz
then return ()
else Left (TypeError ctx e (IfBranchMismatch y z ty tz))
return ty
typeWith _ Natural = do
return (Const Type)
typeWith _ (NaturalLit _ ) = do
return Natural
typeWith _ NaturalFold = do
return
(Pi "_" Natural
(Pi "natural" (Const Type)
(Pi "succ" (Pi "_" "natural" "natural")
(Pi "zero" "natural" "natural") ) ) )
typeWith _ NaturalBuild = do
return
(Pi "_"
(Pi "natural" (Const Type)
(Pi "succ" (Pi "_" "natural" "natural")
(Pi "zero" "natural" "natural") ) )
Natural )
typeWith _ NaturalIsZero = do
return (Pi "_" Natural Bool)
typeWith _ NaturalEven = do
return (Pi "_" Natural Bool)
typeWith _ NaturalOdd = do
return (Pi "_" Natural Bool)
typeWith ctx e@(NaturalPlus l r) = do
tl <- fmap Dhall.Core.normalize (typeWith ctx l)
case tl of
Natural -> return ()
_ -> Left (TypeError ctx e (CantAdd l tl))
tr <- fmap Dhall.Core.normalize (typeWith ctx r)
case tr of
Natural -> return ()
_ -> Left (TypeError ctx e (CantAdd r tr))
return Natural
typeWith ctx e@(NaturalTimes l r) = do
tl <- fmap Dhall.Core.normalize (typeWith ctx l)
case tl of
Natural -> return ()
_ -> Left (TypeError ctx e (CantMultiply l tl))
tr <- fmap Dhall.Core.normalize (typeWith ctx r)
case tr of
Natural -> return ()
_ -> Left (TypeError ctx e (CantMultiply r tr))
return Natural
typeWith _ Integer = do
return (Const Type)
typeWith _ (IntegerLit _ ) = do
return Integer
typeWith _ Double = do
return (Const Type)
typeWith _ (DoubleLit _ ) = do
return Double
typeWith _ Text = do
return (Const Type)
typeWith _ (TextLit _ ) = do
return Text
typeWith ctx e@(TextAppend l r ) = do
tl <- fmap Dhall.Core.normalize (typeWith ctx l)
case tl of
Text -> return ()
_ -> Left (TypeError ctx e (CantTextAppend l tl))
tr <- fmap Dhall.Core.normalize (typeWith ctx r)
case tr of
Text -> return ()
_ -> Left (TypeError ctx e (CantTextAppend r tr))
return Text
typeWith _ List = do
return (Pi "_" (Const Type) (Const Type))
typeWith ctx e@(ListLit Nothing xs) = do
if Data.Vector.null xs
then Left (TypeError ctx e MissingListType)
else do
t <- typeWith ctx (Data.Vector.head xs)
s <- fmap Dhall.Core.normalize (typeWith ctx t)
case s of
Const Type -> return ()
_ -> Left (TypeError ctx e (InvalidListType t))
flip Data.Vector.imapM_ xs (\i x -> do
t' <- typeWith ctx x
if propEqual t t'
then return ()
else do
let nf_t = Dhall.Core.normalize t
let nf_t' = Dhall.Core.normalize t'
let err = MismatchedListElements i nf_t x nf_t'
Left (TypeError ctx e err) )
return (App List t)
typeWith ctx e@(ListLit (Just t ) xs) = do
s <- fmap Dhall.Core.normalize (typeWith ctx t)
case s of
Const Type -> return ()
_ -> Left (TypeError ctx e (InvalidListType t))
flip Data.Vector.imapM_ xs (\i x -> do
t' <- typeWith ctx x
if propEqual t t'
then return ()
else do
let nf_t = Dhall.Core.normalize t
let nf_t' = Dhall.Core.normalize t'
Left (TypeError ctx e (InvalidListElement i nf_t x nf_t')) )
return (App List t)
typeWith _ ListBuild = do
return
(Pi "a" (Const Type)
(Pi "_"
(Pi "list" (Const Type)
(Pi "cons" (Pi "_" "a" (Pi "_" "list" "list"))
(Pi "nil" "list" "list") ) )
(App List "a") ) )
typeWith _ ListFold = do
return
(Pi "a" (Const Type)
(Pi "_" (App List "a")
(Pi "list" (Const Type)
(Pi "cons" (Pi "_" "a" (Pi "_" "list" "list"))
(Pi "nil" "list" "list")) ) ) )
typeWith _ ListLength = do
return (Pi "a" (Const Type) (Pi "_" (App List "a") Natural))
typeWith _ ListHead = do
return (Pi "a" (Const Type) (Pi "_" (App List "a") (App Optional "a")))
typeWith _ ListLast = do
return (Pi "a" (Const Type) (Pi "_" (App List "a") (App Optional "a")))
typeWith _ ListIndexed = do
let kts = [("index", Natural), ("value", "a")]
return
(Pi "a" (Const Type)
(Pi "_" (App List "a")
(App List (Record (Data.Map.fromList kts))) ) )
typeWith _ ListReverse = do
return (Pi "a" (Const Type) (Pi "_" (App List "a") (App List "a")))
typeWith _ Optional = do
return (Pi "_" (Const Type) (Const Type))
typeWith ctx e@(OptionalLit t xs) = do
s <- fmap Dhall.Core.normalize (typeWith ctx t)
case s of
Const Type -> return ()
_ -> Left (TypeError ctx e (InvalidOptionalType t))
let n = Data.Vector.length xs
if 2 <= n
then Left (TypeError ctx e (InvalidOptionalLiteral n))
else return ()
forM_ xs (\x -> do
t' <- typeWith ctx x
if propEqual t t'
then return ()
else do
let nf_t = Dhall.Core.normalize t
let nf_t' = Dhall.Core.normalize t'
Left (TypeError ctx e (InvalidOptionalElement nf_t x nf_t')) )
return (App Optional t)
typeWith _ OptionalFold = do
return
(Pi "a" (Const Type)
(Pi "_" (App Optional "a")
(Pi "optional" (Const Type)
(Pi "just" (Pi "_" "a" "optional")
(Pi "nothing" "optional" "optional") ) ) ) )
typeWith ctx e@(Record kts ) = do
let process (k, t) = do
s <- fmap Dhall.Core.normalize (typeWith ctx t)
case s of
Const Type -> return ()
_ -> Left (TypeError ctx e (InvalidFieldType k t))
mapM_ process (Data.Map.toList kts)
return (Const Type)
typeWith ctx e@(RecordLit kvs ) = do
let process (k, v) = do
t <- typeWith ctx v
s <- fmap Dhall.Core.normalize (typeWith ctx t)
case s of
Const Type -> return ()
_ -> Left (TypeError ctx e (InvalidField k v))
return (k, t)
kts <- mapM process (Data.Map.toAscList kvs)
return (Record (Data.Map.fromAscList kts))
typeWith ctx e@(Union kts ) = do
let process (k, t) = do
s <- fmap Dhall.Core.normalize (typeWith ctx t)
case s of
Const Type -> return ()
_ -> Left (TypeError ctx e (InvalidAlternativeType k t))
mapM_ process (Data.Map.toList kts)
return (Const Type)
typeWith ctx e@(UnionLit k v kts) = do
case Data.Map.lookup k kts of
Just _ -> Left (TypeError ctx e (DuplicateAlternative k))
Nothing -> return ()
t <- typeWith ctx v
let union = Union (Data.Map.insert k t kts)
_ <- typeWith ctx union
return union
typeWith ctx e@(Combine kvsX kvsY) = do
tKvsX <- fmap Dhall.Core.normalize (typeWith ctx kvsX)
ktsX <- case tKvsX of
Record kts -> return kts
_ -> Left (TypeError ctx e (MustCombineARecord kvsX tKvsX))
tKvsY <- fmap Dhall.Core.normalize (typeWith ctx kvsY)
ktsY <- case tKvsY of
Record kts -> return kts
_ -> Left (TypeError ctx e (MustCombineARecord kvsY tKvsY))
let combineTypes ktsL ktsR = do
let ks =
Data.Set.union (Data.Map.keysSet ktsL) (Data.Map.keysSet ktsR)
kts <- forM (toList ks) (\k -> do
case (Data.Map.lookup k ktsL, Data.Map.lookup k ktsR) of
(Just (Record ktsL'), Just (Record ktsR')) -> do
t <- combineTypes ktsL' ktsR'
return (k, t)
(Nothing, Just t) -> do
return (k, t)
(Just t, Nothing) -> do
return (k, t)
_ -> do
Left (TypeError ctx e (FieldCollision k)) )
return (Record (Data.Map.fromList kts))
combineTypes ktsX ktsY
typeWith ctx e@(Merge kvsX kvsY t) = do
tKvsX <- fmap Dhall.Core.normalize (typeWith ctx kvsX)
ktsX <- case tKvsX of
Record kts -> return kts
_ -> Left (TypeError ctx e (MustMergeARecord kvsX tKvsX))
let ksX = Data.Map.keysSet ktsX
tKvsY <- fmap Dhall.Core.normalize (typeWith ctx kvsY)
ktsY <- case tKvsY of
Union kts -> return kts
_ -> Left (TypeError ctx e (MustMergeUnion kvsY tKvsY))
let ksY = Data.Map.keysSet ktsY
let diffX = Data.Set.difference ksX ksY
let diffY = Data.Set.difference ksY ksX
if Data.Set.null diffX
then return ()
else Left (TypeError ctx e (UnusedHandler diffX))
let process (kY, tY) = do
case Data.Map.lookup kY ktsX of
Nothing -> Left (TypeError ctx e (MissingHandler diffY))
Just tX ->
case tX of
Pi _ tY' t' -> do
if propEqual tY tY'
then return ()
else Left (TypeError ctx e (HandlerInputTypeMismatch kY tY tY'))
if propEqual t t'
then return ()
else Left (TypeError ctx e (HandlerOutputTypeMismatch kY t t'))
_ -> Left (TypeError ctx e (HandlerNotAFunction kY tX))
mapM_ process (Data.Map.toList ktsY)
return t
typeWith ctx e@(Field r x ) = do
t <- fmap Dhall.Core.normalize (typeWith ctx r)
case t of
Record kts ->
case Data.Map.lookup x kts of
Just t' -> return t'
Nothing -> Left (TypeError ctx e (MissingField x t))
_ -> Left (TypeError ctx e (NotARecord x r t))
typeWith ctx (Note s e' ) = case typeWith ctx e' of
Left (TypeError ctx' (Note s' e'') m) -> Left (TypeError ctx' (Note s' e'') m)
Left (TypeError ctx' e'' m) -> Left (TypeError ctx' (Note s e'') m)
Right r -> Right r
typeWith _ (Embed p ) = do
absurd p
typeOf :: Expr s X -> Either (TypeError s) (Expr s X)
typeOf = typeWith Dhall.Context.empty
newtype X = X { absurd :: forall a . a }
instance Show X where
show = absurd
instance Buildable X where
build = absurd
data TypeMessage s
= UnboundVariable
| InvalidInputType (Expr s X)
| InvalidOutputType (Expr s X)
| NotAFunction (Expr s X) (Expr s X)
| TypeMismatch (Expr s X) (Expr s X) (Expr s X) (Expr s X)
| AnnotMismatch (Expr s X) (Expr s X) (Expr s X)
| Untyped
| MissingListType
| MismatchedListElements Int (Expr s X) (Expr s X) (Expr s X)
| InvalidListElement Int (Expr s X) (Expr s X) (Expr s X)
| InvalidListType (Expr s X)
| InvalidOptionalElement (Expr s X) (Expr s X) (Expr s X)
| InvalidOptionalLiteral Int
| InvalidOptionalType (Expr s X)
| InvalidPredicate (Expr s X) (Expr s X)
| IfBranchMismatch (Expr s X) (Expr s X) (Expr s X) (Expr s X)
| IfBranchMustBeTerm Bool (Expr s X) (Expr s X) (Expr s X)
| InvalidField Text (Expr s X)
| InvalidFieldType Text (Expr s X)
| InvalidAlternative Text (Expr s X)
| InvalidAlternativeType Text (Expr s X)
| DuplicateAlternative Text
| MustCombineARecord (Expr s X) (Expr s X)
| FieldCollision Text
| MustMergeARecord (Expr s X) (Expr s X)
| MustMergeUnion (Expr s X) (Expr s X)
| UnusedHandler (Set Text)
| MissingHandler (Set Text)
| HandlerInputTypeMismatch Text (Expr s X) (Expr s X)
| HandlerOutputTypeMismatch Text (Expr s X) (Expr s X)
| HandlerNotAFunction Text (Expr s X)
| NotARecord Text (Expr s X) (Expr s X)
| MissingField Text (Expr s X)
| CantAnd (Expr s X) (Expr s X)
| CantOr (Expr s X) (Expr s X)
| CantEQ (Expr s X) (Expr s X)
| CantNE (Expr s X) (Expr s X)
| CantTextAppend (Expr s X) (Expr s X)
| CantAdd (Expr s X) (Expr s X)
| CantMultiply (Expr s X) (Expr s X)
| NoDependentLet (Expr s X) (Expr s X)
| NoDependentTypes (Expr s X) (Expr s X)
deriving (Show)
shortTypeMessage :: TypeMessage s -> Builder
shortTypeMessage msg =
"\ESC[1;31mError\ESC[0m: " <> build short <> "\n"
where
ErrorMessages {..} = prettyTypeMessage msg
longTypeMessage :: TypeMessage s -> Builder
longTypeMessage msg =
"\ESC[1;31mError\ESC[0m: " <> build short <> "\n"
<> "\n"
<> long
where
ErrorMessages {..} = prettyTypeMessage msg
data ErrorMessages = ErrorMessages
{ short :: Builder
, long :: Builder
}
_NOT :: Data.Text.Text
_NOT = "\ESC[1mnot\ESC[0m"
prettyTypeMessage :: TypeMessage s -> ErrorMessages
prettyTypeMessage UnboundVariable = ErrorMessages {..}
where
short = "Unbound variable"
long =
Builder.fromText [NeatInterpolation.text|
Explanation: Expressions can only reference previously introduced (i.e. "bound")
variables that are still "in scope"
For example, the following valid expressions introduce a "bound" variable named
❰x❱:
┌─────────────────┐
│ λ(x : Bool) → x │ Anonymous functions introduce "bound" variables
└─────────────────┘
⇧
This is the bound variable
┌─────────────────┐
│ let x = 1 in x │ ❰let❱ expressions introduce "bound" variables
└─────────────────┘
⇧
This is the bound variable
However, the following expressions are not valid because they all reference a
variable that has not been introduced yet (i.e. an "unbound" variable):
┌─────────────────┐
│ λ(x : Bool) → y │ The variable ❰y❱ hasn't been introduced yet
└─────────────────┘
⇧
This is the unbound variable
┌──────────────────────────┐
│ (let x = True in x) && x │ ❰x❱ is undefined outside the parentheses
└──────────────────────────┘
⇧
This is the unbound variable
┌────────────────┐
│ let x = x in x │ The definition for ❰x❱ cannot reference itself
└────────────────┘
⇧
This is the unbound variable
Some common reasons why you might get this error:
● You misspell a variable name, like this:
┌────────────────────────────────────────────────────┐
│ λ(empty : Bool) → if emty then "Empty" else "Full" │
└────────────────────────────────────────────────────┘
⇧
Typo
● You misspell a reserved identifier, like this:
┌──────────────────────────┐
│ foral (a : Type) → a → a │
└──────────────────────────┘
⇧
Typo
● You tried to define a recursive value, like this:
┌─────────────────────┐
│ let x = x + +1 in x │
└─────────────────────┘
⇧
Recursive definitions are not allowed
● You accidentally forgot a ❰λ❱ or ❰∀❱/❰forall❱
Unbound variable
⇩
┌─────────────────┐
│ (x : Bool) → x │
└─────────────────┘
⇧
A ❰λ❱ here would transform this into a valid anonymous function
Unbound variable
⇩
┌────────────────────┐
│ (x : Bool) → Bool │
└────────────────────┘
⇧
A ❰∀❱ or ❰forall❱ here would transform this into a valid function type
|]
prettyTypeMessage (InvalidInputType expr) = ErrorMessages {..}
where
short = "Invalid function input"
long =
Builder.fromText [NeatInterpolation.text|
Explanation: A function can accept an input "term" that has a given "type", like
this:
This is the input term that the function accepts
⇩
┌───────────────────────┐
│ ∀(x : Natural) → Bool │ This is the type of a function that accepts an
└───────────────────────┘ input term named ❰x❱ that has type ❰Natural❱
⇧
This is the type of the input term
┌────────────────┐
│ Bool → Integer │ This is the type of a function that accepts an anonymous
└────────────────┘ input term that has type ❰Bool❱
⇧
This is the type of the input term
... or a function can accept an input "type" that has a given "kind", like this:
This is the input type that the function accepts
⇩
┌────────────────────┐
│ ∀(a : Type) → Type │ This is the type of a function that accepts an input
└────────────────────┘ type named ❰a❱ that has kind ❰Type❱
⇧
This is the kind of the input type
┌──────────────────────┐
│ (Type → Type) → Type │ This is the type of a function that accepts an
└──────────────────────┘ anonymous input type that has kind ❰Type → Type❱
⇧
This is the kind of the input type
Other function inputs are $_NOT valid, like this:
┌──────────────┐
│ ∀(x : 1) → x │ ❰1❱ is a "term" and not a "type" nor a "kind" so ❰x❱
└──────────────┘ cannot have "type" ❰1❱ or "kind" ❰1❱
⇧
This is not a type or kind
┌──────────┐
│ True → x │ ❰True❱ is a "term" and not a "type" nor a "kind" so the
└──────────┘ anonymous input cannot have "type" ❰True❱ or "kind" ❰True❱
⇧
This is not a type or kind
You annotated a function input with the following expression:
↳ $txt
... which is neither a type nor a kind
|]
where
txt = Text.toStrict (Dhall.Core.pretty expr)
prettyTypeMessage (InvalidOutputType expr) = ErrorMessages {..}
where
short = "Invalid function output"
long =
Builder.fromText [NeatInterpolation.text|
Explanation: A function can return an output "term" that has a given "type",
like this:
┌────────────────────┐
│ ∀(x : Text) → Bool │ This is the type of a function that returns an
└────────────────────┘ output term that has type ❰Bool❱
⇧
This is the type of the output term
┌────────────────┐
│ Bool → Integer │ This is the type of a function that returns an output
└────────────────┘ term that has type ❰Int❱
⇧
This is the type of the output term
... or a function can return an output "type" that has a given "kind", like
this:
┌────────────────────┐
│ ∀(a : Type) → Type │ This is the type of a function that returns an
└────────────────────┘ output type that has kind ❰Type❱
⇧
This is the kind of the output type
┌──────────────────────┐
│ (Type → Type) → Type │ This is the type of a function that returns an
└──────────────────────┘ output type that has kind ❰Type❱
⇧
This is the kind of the output type
Other outputs are $_NOT valid, like this:
┌─────────────────┐
│ ∀(x : Bool) → x │ ❰x❱ is a "term" and not a "type" nor a "kind" so the
└─────────────────┘ output cannot have "type" ❰x❱ or "kind" ❰x❱
⇧
This is not a type or kind
┌─────────────┐
│ Text → True │ ❰True❱ is a "term" and not a "type" nor a "kind" so the
└─────────────┘ output cannot have "type" ❰True❱ or "kind" ❰True❱
⇧
This is not a type or kind
You specified that your function outputs a:
↳ $txt
... which is neither a type nor a kind:
Some common reasons why you might get this error:
● You use ❰∀❱ instead of ❰λ❱ by mistake, like this:
┌────────────────┐
│ ∀(x: Bool) → x │
└────────────────┘
⇧
Using ❰λ❱ here instead of ❰∀❱ would transform this into a valid function
|]
where
txt = Text.toStrict (Dhall.Core.pretty expr)
prettyTypeMessage (NotAFunction expr0 expr1) = ErrorMessages {..}
where
short = "Not a function"
long =
Builder.fromText [NeatInterpolation.text|
Explanation: Expressions separated by whitespace denote function application,
like this:
┌─────┐
│ f x │ This denotes the function ❰f❱ applied to an argument named ❰x❱
└─────┘
A function is a term that has type ❰a → b❱ for some ❰a❱ or ❰b❱. For example,
the following expressions are all functions because they have a function type:
The function's input type is ❰Bool❱
⇩
┌───────────────────────────────┐
│ λ(x : Bool) → x : Bool → Bool │ Userdefined anonymous function
└───────────────────────────────┘
⇧
The function's output type is ❰Bool❱
The function's input type is ❰Natural❱
⇩
┌───────────────────────────────┐
│ Natural/even : Natural → Bool │ Builtin function
└───────────────────────────────┘
⇧
The function's output type is ❰Bool❱
The function's input kind is ❰Type❱
⇩
┌───────────────────────────────┐
│ λ(a : Type) → a : Type → Type │ Typelevel functions are still functions
└───────────────────────────────┘
⇧
The function's output kind is ❰Type❱
The function's input kind is ❰Type❱
⇩
┌────────────────────┐
│ List : Type → Type │ Builtin typelevel function
└────────────────────┘
⇧
The function's output kind is ❰Type❱
Function's input has kind ❰Type❱
⇩
┌─────────────────────────────────────────────────┐
│ List/head : ∀(a : Type) → (List a → Optional a) │ A function can return
└─────────────────────────────────────────────────┘ another function
⇧
Function's output has type ❰List a → Optional a❱
The function's input type is ❰List Text❱
⇩
┌────────────────────────────────────────────┐
│ List/head Text : List Text → Optional Text │ A function applied to an
└────────────────────────────────────────────┘ argument can be a function
⇧
The function's output type is ❰Optional Text❱
An expression is not a function if the expression's type is not of the form
❰a → b❱. For example, these are $_NOT functions:
┌─────────────┐
│ 1 : Integer │ ❰1❱ is not a function because ❰Integer❱ is not the type of
└─────────────┘ a function
┌────────────────────────┐
│ Natural/even +2 : Bool │ ❰Natural/even +2❱ is not a function because
└────────────────────────┘ ❰Bool❱ is not the type of a function
┌──────────────────┐
│ List Text : Type │ ❰List Text❱ is not a function because ❰Type❱ is not
└──────────────────┘ the type of a function
You tried to use the following expression as a function:
↳ $txt0
... but this expression's type is:
↳ $txt1
... which is not a function type
Some common reasons why you might get this error:
● You tried to add two ❰Integer❱s without a space around the ❰+❱, like this:
┌─────┐
│ 2+2 │
└─────┘
The above code is parsed as:
┌────────┐
│ 2 (+2) │
└────────┘
⇧
The compiler thinks that this ❰2❱ is a function whose argument is ❰+2❱
This is because the ❰+❱ symbol has two meanings: you use ❰+❱ to add two
numbers, but you also can prefix ❰Integer❱ literals with a ❰+❱ to turn them
into ❰Natural❱ literals (like ❰+2❱)
To fix the code, you need to put spaces around the ❰+❱ and also prefix each
❰2❱ with a ❰+❱, like this:
┌─────────┐
│ +2 + +2 │
└─────────┘
You can only add ❰Natural❱ numbers, which is why you must also change each
❰2❱ to ❰+2❱
|]
where
txt0 = Text.toStrict (Dhall.Core.pretty expr0)
txt1 = Text.toStrict (Dhall.Core.pretty expr1)
prettyTypeMessage (TypeMismatch expr0 expr1 expr2 expr3) = ErrorMessages {..}
where
short = "Wrong type of function argument"
long =
Builder.fromText [NeatInterpolation.text|
Explanation: Every function declares what type or kind of argument to accept
For example:
┌───────────────────────────────┐
│ λ(x : Bool) → x : Bool → Bool │ This anonymous function only accepts
└───────────────────────────────┘ arguments that have type ❰Bool❱
⇧
The function's input type
┌───────────────────────────────┐
│ Natural/even : Natural → Bool │ This builtin function only accepts
└───────────────────────────────┘ arguments that have type ❰Natural❱
⇧
The function's input type
┌───────────────────────────────┐
│ λ(a : Type) → a : Type → Type │ This anonymous function only accepts
└───────────────────────────────┘ arguments that have kind ❰Type❱
⇧
The function's input kind
┌────────────────────┐
│ List : Type → Type │ This builtin function only accepts arguments that
└────────────────────┘ have kind ❰Type❱
⇧
The function's input kind
For example, the following expressions are valid:
┌────────────────────────┐
│ (λ(x : Bool) → x) True │ ❰True❱ has type ❰Bool❱, which matches the type
└────────────────────────┘ of argument that the anonymous function accepts
┌─────────────────┐
│ Natural/even +2 │ ❰+2❱ has type ❰Natural❱, which matches the type of
└─────────────────┘ argument that the ❰Natural/even❱ function accepts,
┌────────────────────────┐
│ (λ(a : Type) → a) Bool │ ❰Bool❱ has kind ❰Type❱, which matches the kind
└────────────────────────┘ of argument that the anonymous function accepts
┌───────────┐
│ List Text │ ❰Text❱ has kind ❰Type❱, which matches the kind of argument
└───────────┘ that that the ❰List❱ function accepts
However, you can $_NOT apply a function to the wrong type or kind of argument
For example, the following expressions are not valid:
┌───────────────────────┐
│ (λ(x : Bool) → x) "A" │ ❰"A"❱ has type ❰Text❱, but the anonymous function
└───────────────────────┘ expects an argument that has type ❰Bool❱
┌──────────────────┐
│ Natural/even "A" │ ❰"A"❱ has type ❰Text❱, but the ❰Natural/even❱ function
└──────────────────┘ expects an argument that has type ❰Natural❱
┌────────────────────────┐
│ (λ(a : Type) → a) True │ ❰True❱ has type ❰Bool❱, but the anonymous
└────────────────────────┘ function expects an argument of kind ❰Type❱
┌────────┐
│ List 1 │ ❰1❱ has type ❰Integer❱, but the ❰List❱ function expects an
└────────┘ argument that has kind ❰Type❱
You tried to invoke the following function:
↳ $txt0
... which expects an argument of type or kind:
↳ $txt1
... on the following argument:
↳ $txt2
... which has a different type or kind:
↳ $txt3
Some common reasons why you might get this error:
● You omit a function argument by mistake:
┌───────────────────────┐
│ List/head [1, 2, 3] │
└───────────────────────┘
⇧
❰List/head❱ is missing the first argument,
which should be: ❰Integer❱
● You supply an ❰Integer❱ literal to a function that expects a ❰Natural❱
┌────────────────┐
│ Natural/even 2 │
└────────────────┘
⇧
This should be ❰+2❱
|]
where
txt0 = Text.toStrict (Dhall.Core.pretty expr0)
txt1 = Text.toStrict (Dhall.Core.pretty expr1)
txt2 = Text.toStrict (Dhall.Core.pretty expr2)
txt3 = Text.toStrict (Dhall.Core.pretty expr3)
prettyTypeMessage (AnnotMismatch expr0 expr1 expr2) = ErrorMessages {..}
where
short = "Expression doesn't match annotation"
long =
Builder.fromText [NeatInterpolation.text|
Explanation: You can annotate an expression with its type or kind using the
❰:❱ symbol, like this:
┌───────┐
│ x : t │ ❰x❱ is an expression and ❰t❱ is the annotated type or kind of ❰x❱
└───────┘
The type checker verifies that the expression's type or kind matches the
provided annotation
For example, all of the following are valid annotations that the type checker
accepts:
┌─────────────┐
│ 1 : Integer │ ❰1❱ is an expression that has type ❰Integer❱, so the type
└─────────────┘ checker accepts the annotation
┌────────────────────────┐
│ Natural/even +2 : Bool │ ❰Natural/even +2❱ has type ❰Bool❱, so the type
└────────────────────────┘ checker accepts the annotation
┌────────────────────┐
│ List : Type → Type │ ❰List❱ is an expression that has kind ❰Type → Type❱,
└────────────────────┘ so the type checker accepts the annotation
┌──────────────────┐
│ List Text : Type │ ❰List Text❱ is an expression that has kind ❰Type❱, so
└──────────────────┘ the type checker accepts the annotation
However, the following annotations are $_NOT valid and the type checker will
reject them:
┌──────────┐
│ 1 : Text │ The type checker rejects this because ❰1❱ does not have type
└──────────┘ ❰Text❱
┌─────────────┐
│ List : Type │ ❰List❱ does not have kind ❰Type❱
└─────────────┘
You or the interpreter annotated this expression:
↳ $txt0
... with this type or kind:
↳ $txt1
... but the inferred type or kind of the expression is actually:
↳ $txt2
Some common reasons why you might get this error:
● The Haskell Dhall interpreter implicitly inserts a toplevel annotation
matching the expected type
For example, if you run the following Haskell code:
┌───────────────────────────────┐
│ >>> input auto "1" :: IO Text │
└───────────────────────────────┘
... then the interpreter will actually type check the following annotated
expression:
┌──────────┐
│ 1 : Text │
└──────────┘
... and then typechecking will fail
|]
where
txt0 = Text.toStrict (Dhall.Core.pretty expr0)
txt1 = Text.toStrict (Dhall.Core.pretty expr1)
txt2 = Text.toStrict (Dhall.Core.pretty expr2)
prettyTypeMessage Untyped = ErrorMessages {..}
where
short = "❰Kind❱ has no type or kind"
long =
Builder.fromText [NeatInterpolation.text|
Explanation: There are four levels of expressions that form a heirarchy:
● terms
● types
● kinds
● sorts
The following example illustrates this heirarchy:
┌────────────────────────────┐
│ "ABC" : Text : Type : Kind │
└────────────────────────────┘
⇧ ⇧ ⇧ ⇧
term type kind sort
There is nothing above ❰Kind❱ in this hierarchy, so if you try to type check any
expression containing ❰Kind❱ anywhere in the expression then type checking fails
Some common reasons why you might get this error:
● You supplied a kind where a type was expected
For example, the following expression will fail to type check:
┌────────────────┐
│ [] : List Type │
└────────────────┘
⇧
❰Type❱ is a kind, not a type
|]
prettyTypeMessage (InvalidPredicate expr0 expr1) = ErrorMessages {..}
where
short = "Invalid predicate for ❰if❱"
long =
Builder.fromText [NeatInterpolation.text|
Explanation: Every ❰if❱ expression begins with a predicate which must have type
❰Bool❱
For example, these are valid ❰if❱ expressions:
┌──────────────────────────────┐
│ if True then "Yes" else "No" │
└──────────────────────────────┘
⇧
Predicate
┌─────────────────────────────────────────┐
│ λ(x : Bool) → if x then False else True │
└─────────────────────────────────────────┘
⇧
Predicate
... but these are $_NOT valid ❰if❱ expressions:
┌───────────────────────────┐
│ if 0 then "Yes" else "No" │ ❰0❱ does not have type ❰Bool❱
└───────────────────────────┘
┌────────────────────────────┐
│ if "" then False else True │ ❰""❱ does not have type ❰Bool❱
└────────────────────────────┘
Your ❰if❱ expression begins with the following predicate:
↳ $txt0
... that has type:
↳ $txt1
... but the predicate must instead have type ❰Bool❱
Some common reasons why you might get this error:
● You might be used to other programming languages that accept predicates other
than ❰Bool❱
For example, some languages permit ❰0❱ or ❰""❱ as valid predicates and treat
them as equivalent to ❰False❱. However, the Dhall language does not permit
this
|]
where
txt0 = Text.toStrict (Dhall.Core.pretty expr0)
txt1 = Text.toStrict (Dhall.Core.pretty expr1)
prettyTypeMessage (IfBranchMustBeTerm b expr0 expr1 expr2) =
ErrorMessages {..}
where
short = "❰if❱ branch is not a term"
long =
Builder.fromText [NeatInterpolation.text|
Explanation: Every ❰if❱ expression has a ❰then❱ and ❰else❱ branch, each of which
is an expression:
Expression for ❰then❱ branch
⇩
┌────────────────────────────────┐
│ if True then "Hello, world!" │
│ else "Goodbye, world!" │
└────────────────────────────────┘
⇧
Expression for ❰else❱ branch
These expressions must be a "term", where a "term" is defined as an expression
that has a type thas has kind ❰Type❱
For example, the following expressions are all valid "terms":
┌────────────────────┐
│ 1 : Integer : Type │ ❰1❱ is a term with a type (❰Integer❱) of kind ❰Type❱
└────────────────────┘
⇧
term
┌─────────────────────────────────────┐
│ Natural/odd : Natural → Bool : Type │ ❰Natural/odd❱ is a term with a type
└─────────────────────────────────────┘ (❰Natural → Bool❱) of kind ❰Type❱
⇧
term
However, the following expressions are $_NOT valid terms:
┌────────────────────┐
│ Text : Type : Kind │ ❰Text❱ has kind (❰Type❱) of sort ❰Kind❱ and is
└────────────────────┘ therefore not a term
⇧
type
┌───────────────────────────┐
│ List : Type → Type : Kind │ ❰List❱ has kind (❰Type → Type❱) of sort
└───────────────────────────┘ ❰Kind❱ and is therefore not a term
⇧
typelevel function
This means that you cannot define an ❰if❱ expression that returns a type. For
example, the following ❰if❱ expression is $_NOT valid:
┌─────────────────────────────┐
│ if True then Text else Bool │ Invalid ❰if❱ expression
└─────────────────────────────┘
⇧ ⇧
type type
Your ❰$txt0❱ branch of your ❰if❱ expression is:
↳ $txt1
... which has kind:
↳ $txt2
... of sort:
↳ $txt3
... and is not a term. Therefore your ❰if❱ expression is not valid
|]
where
txt0 = if b then "then" else "else"
txt1 = Text.toStrict (Dhall.Core.pretty expr0)
txt2 = Text.toStrict (Dhall.Core.pretty expr1)
txt3 = Text.toStrict (Dhall.Core.pretty expr2)
prettyTypeMessage (IfBranchMismatch expr0 expr1 expr2 expr3) =
ErrorMessages {..}
where
short = "❰if❱ branches must have matching types"
long =
Builder.fromText [NeatInterpolation.text|
Explanation: Every ❰if❱ expression has a ❰then❱ and ❰else❱ branch, each of which
is an expression:
Expression for ❰then❱ branch
⇩
┌────────────────────────────────┐
│ if True then "Hello, world!" │
│ else "Goodbye, world!" │
└────────────────────────────────┘
⇧
Expression for ❰else❱ branch
These two expressions must have the same type. For example, the following ❰if❱
expressions are all valid:
┌──────────────────────────────────┐
│ λ(b : Bool) → if b then 0 else 1 │ Both branches have type ❰Integer❱
└──────────────────────────────────┘
┌────────────────────────────┐
│ λ(b : Bool) → │
│ if b then Natural/even │ Both branches have type ❰Natural → Bool❱
│ else Natural/odd │
└────────────────────────────┘
However, the following expression is $_NOT valid:
This branch has type ❰Integer❱
⇩
┌────────────────────────┐
│ if True then 0 │
│ else "ABC" │
└────────────────────────┘
⇧
This branch has type ❰Text❱
The ❰then❱ and ❰else❱ branches must have matching types, even if the predicate is
always ❰True❱ or ❰False❱
Your ❰if❱ expression has the following ❰then❱ branch:
↳ $txt0
... which has type:
↳ $txt2
... and the following ❰else❱ branch:
↳ $txt1
... which has a different type:
↳ $txt3
Fix your ❰then❱ and ❰else❱ branches to have matching types
|]
where
txt0 = Text.toStrict (Dhall.Core.pretty expr0)
txt1 = Text.toStrict (Dhall.Core.pretty expr1)
txt2 = Text.toStrict (Dhall.Core.pretty expr2)
txt3 = Text.toStrict (Dhall.Core.pretty expr3)
prettyTypeMessage (InvalidListType expr0) = ErrorMessages {..}
where
short = "Invalid type for ❰List❱ elements"
long =
Builder.fromText [NeatInterpolation.text|
Explanation: ❰List❱s can optionally document the type of their elements with a
type annotation, like this:
┌──────────────────────────┐
│ [1, 2, 3] : List Integer │ A ❰List❱ of three ❰Integer❱s
└──────────────────────────┘
⇧
The type of the ❰List❱'s elements, which are ❰Integer❱s
┌───────────────────┐
│ [] : List Integer │ An empty ❰List❱
└───────────────────┘
⇧
You must specify the type when the ❰List❱ is empty
The element type must be a type and not something else. For example, the
following element types are $_NOT valid:
┌──────────────┐
│ ... : List 1 │
└──────────────┘
⇧
This is an ❰Integer❱ and not a ❰Type❱
┌─────────────────┐
│ ... : List Type │
└─────────────────┘
⇧
This is a ❰Kind❱ and not a ❰Type❱
You declared that the ❰List❱'s elements should have type:
↳ $txt0
... which is not a ❰Type❱
|]
where
txt0 = Text.toStrict (Dhall.Core.pretty expr0)
prettyTypeMessage MissingListType = do
ErrorMessages {..}
where
short = "Empty lists need a type annotation"
long =
Builder.fromText [NeatInterpolation.text|
Explanation: Lists do not require a type annotation if they have at least one
element:
┌───────────┐
│ [1, 2, 3] │ The compiler can infer that this list has type ❰List Integer❱
└───────────┘
However, empty lists still require a type annotation:
┌───────────────────┐
│ [] : List Integer │ This type annotation is mandatory
└───────────────────┘
You cannot supply an empty list without a type annotation
|]
prettyTypeMessage (MismatchedListElements i expr0 expr1 expr2) =
ErrorMessages {..}
where
short = "List elements should have the same type"
long =
Builder.fromText [NeatInterpolation.text|
Explanation: Every element in a list must have the same type
For example, this is a valid ❰List❱:
┌───────────┐
│ [1, 2, 3] │ Every element in this ❰List❱ is an ❰Integer❱
└───────────┘
.. but this is $_NOT a valid ❰List❱:
┌───────────────┐
│ [1, "ABC", 3] │ The first and second element have different types
└───────────────┘
Your first ❰List❱ elements has this type:
↳ $txt0
... but the following element at index $txt1:
↳ $txt2
... has this type instead:
↳ $txt3
|]
where
txt0 = Text.toStrict (Dhall.Core.pretty expr0)
txt1 = Text.toStrict (Dhall.Core.pretty i )
txt2 = Text.toStrict (Dhall.Core.pretty expr1)
txt3 = Text.toStrict (Dhall.Core.pretty expr2)
prettyTypeMessage (InvalidListElement i expr0 expr1 expr2) =
ErrorMessages {..}
where
short = "List element has the wrong type"
long =
Builder.fromText [NeatInterpolation.text|
Explanation: Every element in the list must have a type matching the type
annotation at the end of the list
For example, this is a valid ❰List❱:
┌──────────────────────────┐
│ [1, 2, 3] : List Integer │ Every element in this ❰List❱ is an ❰Integer❱
└──────────────────────────┘
.. but this is $_NOT a valid ❰List❱:
┌──────────────────────────────┐
│ [1, "ABC", 3] : List Integer │ The second element is not an ❰Integer❱
└──────────────────────────────┘
Your ❰List❱ elements should have this type:
↳ $txt0
... but the following element at index $txt1:
↳ $txt2
... has this type instead:
↳ $txt3
|]
where
txt0 = Text.toStrict (Dhall.Core.pretty expr0)
txt1 = Text.toStrict (Dhall.Core.pretty i )
txt2 = Text.toStrict (Dhall.Core.pretty expr1)
txt3 = Text.toStrict (Dhall.Core.pretty expr2)
prettyTypeMessage (InvalidOptionalType expr0) = ErrorMessages {..}
where
short = "Invalid type for ❰Optional❱ element"
long =
Builder.fromText [NeatInterpolation.text|
Explanation: Every optional element ends with a type annotation for the element
that might be present, like this:
┌────────────────────────┐
│ [1] : Optional Integer │ An optional element that's present
└────────────────────────┘
⇧
The type of the ❰Optional❱ element, which is an ❰Integer❱
┌────────────────────────┐
│ [] : Optional Integer │ An optional element that's absent
└────────────────────────┘
⇧
You still specify the type even when the element is absent
The element type must be a type and not something else. For example, the
following element types are $_NOT valid:
┌──────────────────┐
│ ... : Optional 1 │
└──────────────────┘
⇧
This is an ❰Integer❱ and not a ❰Type❱
┌─────────────────────┐
│ ... : Optional Type │
└─────────────────────┘
⇧
This is a ❰Kind❱ and not a ❰Type❱
Even if the element is absent you still must specify a valid type
You declared that the ❰Optional❱ element should have type:
↳ $txt0
... which is not a ❰Type❱
|]
where
txt0 = Text.toStrict (Dhall.Core.pretty expr0)
prettyTypeMessage (InvalidOptionalElement expr0 expr1 expr2) = ErrorMessages {..}
where
short = "❰Optional❱ element has the wrong type"
long =
Builder.fromText [NeatInterpolation.text|
Explanation: An ❰Optional❱ element must have a type matching the type annotation
For example, this is a valid ❰Optional❱ value:
┌────────────────────────┐
│ [1] : Optional Integer │ ❰1❱ is an ❰Integer❱, which matches the type
└────────────────────────┘
... but this is $_NOT a valid ❰Optional❱ value:
┌────────────────────────────┐
│ ["ABC"] : Optional Integer │ ❰"ABC"❱ is not an ❰Integer❱
└────────────────────────────┘
Your ❰Optional❱ element should have this type:
↳ $txt0
... but the element you provided:
↳ $txt1
... has this type instead:
↳ $txt2
|]
where
txt0 = Text.toStrict (Dhall.Core.pretty expr0)
txt1 = Text.toStrict (Dhall.Core.pretty expr1)
txt2 = Text.toStrict (Dhall.Core.pretty expr2)
prettyTypeMessage (InvalidOptionalLiteral n) = ErrorMessages {..}
where
short = "Multiple ❰Optional❱ elements not allowed"
long =
Builder.fromText [NeatInterpolation.text|
Explanation: The syntax for ❰Optional❱ values resembles the syntax for ❰List❱s:
┌───────────────────────┐
│ [] : Optional Integer │ An ❰Optional❱ value which is absent
└───────────────────────┘
┌───────────────────────┐
│ [] : List Integer │ An empty (0element) ❰List❱
└───────────────────────┘
┌────────────────────────┐
│ [1] : Optional Integer │ An ❰Optional❱ value which is present
└────────────────────────┘
┌────────────────────────┐
│ [1] : List Integer │ A singleton (1element) ❰List❱
└────────────────────────┘
However, an ❰Optional❱ value can $_NOT have more than one element, whereas a
❰List❱ can have multiple elements:
┌───────────────────────────┐
│ [1, 2] : Optional Integer │ Invalid: multiple elements $_NOT allowed
└───────────────────────────┘
┌───────────────────────────┐
│ [1, 2] : List Integer │ Valid: multiple elements allowed
└───────────────────────────┘
Your ❰Optional❱ value had this many elements:
↳ $txt0
... when an ❰Optional❱ value can only have at most one element
Some common reasons why you might get this error:
● You accidentally typed ❰Optional❱ when you meant ❰List❱, like this:
┌────────────────────────────────────────────────────┐
│ List/length Integer ([1, 2, 3] : Optional Integer) │
└────────────────────────────────────────────────────┘
⇧
This should be ❰List❱ instead
|]
where
txt0 = Text.toStrict (Dhall.Core.pretty n)
prettyTypeMessage (InvalidFieldType k expr0) = ErrorMessages {..}
where
short = "Invalid field type"
long =
Builder.fromText [NeatInterpolation.text|
Explanation: Every record type documents the type of each field, like this:
┌──────────────────────────────────────────────┐
│ { foo : Integer, bar : Integer, baz : Text } │
└──────────────────────────────────────────────┘
However, fields cannot be annotated with expressions other than types
For example, these record types are $_NOT valid:
┌────────────────────────────┐
│ { foo : Integer, bar : 1 } │
└────────────────────────────┘
⇧
❰1❱ is an ❰Integer❱ and not a ❰Type❱
┌───────────────────────────────┐
│ { foo : Integer, bar : Type } │
└───────────────────────────────┘
⇧
❰Type❱ is a ❰Kind❱ and not a ❰Type❱
You provided a record type with a key named:
↳ $txt0
... annotated with the following expression:
↳ $txt1
... which is not a type
|]
where
txt0 = Text.toStrict (Dhall.Core.pretty k )
txt1 = Text.toStrict (Dhall.Core.pretty expr0)
prettyTypeMessage (InvalidField k expr0) = ErrorMessages {..}
where
short = "Invalid field"
long =
Builder.fromText [NeatInterpolation.text|
Explanation: Every record literal is a set of fields assigned to values, like
this:
┌────────────────────────────────────────┐
│ { foo = 100, bar = True, baz = "ABC" } │
└────────────────────────────────────────┘
However, fields can only be terms and cannot be types or kinds
For example, these record literals are $_NOT valid:
┌───────────────────────────┐
│ { foo = 100, bar = Text } │
└───────────────────────────┘
⇧
❰Text❱ is a type and not a term
┌───────────────────────────┐
│ { foo = 100, bar = Type } │
└───────────────────────────┘
⇧
❰Type❱ is a kind and not a term
You provided a record literal with a key named:
↳ $txt0
... whose value is:
↳ $txt1
... which is not a term
|]
where
txt0 = Text.toStrict (Dhall.Core.pretty k )
txt1 = Text.toStrict (Dhall.Core.pretty expr0)
prettyTypeMessage (InvalidAlternativeType k expr0) = ErrorMessages {..}
where
short = "Invalid alternative"
long =
Builder.fromText [NeatInterpolation.text|
Explanation: Every union literal begins by selecting one alternative and
specifying the value for that alternative, like this:
Select the ❰Left❱ alternative, whose value is ❰True❱
⇩
┌──────────────────────────────────┐
│ < Left = True, Right : Natural > │ A union literal with two alternatives
└──────────────────────────────────┘
However, this value must be a term and not a type. For example, the following
values are $_NOT valid:
┌──────────────────────────────────┐
│ < Left = Text, Right : Natural > │ Invalid union literal
└──────────────────────────────────┘
⇧
This is a type and not a term
┌───────────────────────────────┐
│ < Left = Type, Right : Type > │ Invalid union type
└───────────────────────────────┘
⇧
This is a kind and not a term
You provided a union literal with an alternative named:
↳ $txt0
... whose value is:
↳ $txt1
... which is not a term
Some common reasons why you might get this error:
● You accidentally typed ❰=❱ instead of ❰:❱ for a union literal with one
alternative:
┌────────────────────┐
│ < Example = Text > │
└────────────────────┘
⇧
This could be ❰:❱ instead
|]
where
txt0 = Text.toStrict (Dhall.Core.pretty k )
txt1 = Text.toStrict (Dhall.Core.pretty expr0)
prettyTypeMessage (InvalidAlternative k expr0) = ErrorMessages {..}
where
short = "Invalid alternative"
long =
Builder.fromText [NeatInterpolation.text|
Explanation: Every union type specifies the type of each alternative, like this:
The type of the first alternative is ❰Bool❱
⇩
┌──────────────────────────────────┐
│ < Left : Bool, Right : Natural > │ A union type with two alternatives
└──────────────────────────────────┘
⇧
The type of the second alternative is ❰Natural❱
However, these alternatives can only be annotated with types. For example, the
following union types are $_NOT valid:
┌────────────────────────────┐
│ < Left : Bool, Right : 1 > │ Invalid union type
└────────────────────────────┘
⇧
This is a term and not a type
┌───────────────────────────────┐
│ < Left : Bool, Right : Type > │ Invalid union type
└───────────────────────────────┘
⇧
This is a kind and not a type
You provided a union type with an alternative named:
↳ $txt0
... annotated with the following expression which is not a type:
↳ $txt1
Some common reasons why you might get this error:
● You accidentally typed ❰:❱ instead of ❰=❱ for a union literal with one
alternative:
┌─────────────────┐
│ < Example : 1 > │
└─────────────────┘
⇧
This could be ❰=❱ instead
|]
where
txt0 = Text.toStrict (Dhall.Core.pretty k )
txt1 = Text.toStrict (Dhall.Core.pretty expr0)
prettyTypeMessage (DuplicateAlternative k) = ErrorMessages {..}
where
short = "Duplicate union alternative"
long =
Builder.fromText [NeatInterpolation.text|
Explanation: Unions may not have two alternatives that share the same name
For example, the following expressions are $_NOT valid:
┌─────────────────────────────┐
│ < foo = True | foo : Text > │ Invalid: ❰foo❱ appears twice
└─────────────────────────────┘
┌───────────────────────────────────────┐
│ < foo = 1 | bar : Bool | bar : Text > │ Invalid: ❰bar❱ appears twice
└───────────────────────────────────────┘
You have more than one alternative named:
↳ $txt0
|]
where
txt0 = Text.toStrict (Dhall.Core.pretty k)
prettyTypeMessage (MustCombineARecord expr0 expr1) = ErrorMessages {..}
where
short = "You can only combine records"
long =
Builder.fromText [NeatInterpolation.text|
Explanation: You can combine records using the ❰∧❱ operator, like this:
┌───────────────────────────────────────────┐
│ { foo = 1, bar = "ABC" } ∧ { baz = True } │
└───────────────────────────────────────────┘
┌─────────────────────────────────────────────┐
│ λ(r : { foo : Bool }) → r ∧ { bar = "ABC" } │
└─────────────────────────────────────────────┘
... but you cannot combine values that are not records.
For example, the following expressions are $_NOT valid:
┌──────────────────────────────┐
│ { foo = 1, bar = "ABC" } ∧ 1 │
└──────────────────────────────┘
⇧
Invalid: Not a record
┌───────────────────────────────────────────┐
│ { foo = 1, bar = "ABC" } ∧ { baz : Bool } │
└───────────────────────────────────────────┘
⇧
Invalid: This is a record type and not a record
┌───────────────────────────────────────────┐
│ { foo = 1, bar = "ABC" } ∧ < baz = True > │
└───────────────────────────────────────────┘
⇧
Invalid: This is a union and not a record
You tried to combine the following value:
↳ $txt0
... which is not a record, but is actually a:
↳ $txt1
|]
where
txt0 = Text.toStrict (Dhall.Core.pretty expr0)
txt1 = Text.toStrict (Dhall.Core.pretty expr1)
prettyTypeMessage (FieldCollision k) = ErrorMessages {..}
where
short = "Field collision"
long =
Builder.fromText [NeatInterpolation.text|
Explanation: You can combine records if they don't share any fields in common,
like this:
┌───────────────────────────────────────────┐
│ { foo = 1, bar = "ABC" } ∧ { baz = True } │
└───────────────────────────────────────────┘
┌────────────────────────────────────────┐
│ λ(r : { baz : Bool}) → { foo = 1 } ∧ r │
└────────────────────────────────────────┘
... but you cannot merge two records that share the same field
For example, the following expression is $_NOT valid:
┌───────────────────────────────────────────┐
│ { foo = 1, bar = "ABC" } ∧ { foo = True } │ Invalid: Colliding ❰foo❱ fields
└───────────────────────────────────────────┘
You combined two records that share the following field:
↳ $txt0
... which is not allowed
Some common reasons why you might get this error:
● You tried to use ❰∧❱ to update a field's value, like this:
┌────────────────────────────────────────┐
│ { foo = 1, bar = "ABC" } ∧ { foo = 2 } │
└────────────────────────────────────────┘
⇧
Invalid attempt to update ❰foo❱'s value to ❰2❱
Field updates are intentionally not allowed as the Dhall language discourages
patchoriented programming
|]
where
txt0 = Text.toStrict k
prettyTypeMessage (MustMergeARecord expr0 expr1) = ErrorMessages {..}
where
short = "❰merge❱ expects a record of handlers"
long =
Builder.fromText [NeatInterpolation.text|
Explanation: You can ❰merge❱ the alternatives of a union using a record with one
handler per alternative, like this:
┌─────────────────────────────────────────────────────────────────────┐
│ let union = < Left = +2 | Right : Bool > │
│ in let handlers = { Left = Natural/even, Right = λ(x : Bool) → x } │
│ in merge handlers union : Bool │
└─────────────────────────────────────────────────────────────────────┘
... but the first argument to ❰merge❱ must be a record and not some other type.
For example, the following expression is $_NOT valid:
┌─────────────────────────────────────────┐
│ let handler = λ(x : Bool) → x │
│ in merge handler < Foo = True > : True │
└─────────────────────────────────────────┘
⇧
Invalid: ❰handler❱ isn't a record
You provided the following handler:
↳ $txt0
... which is not a record, but is actually a value of type:
↳ $txt1
Some common reasons why you might get this error:
● You accidentally provide an empty record type instead of an empty record when
you ❰merge❱ an empty union:
┌──────────────────────────────────────────┐
│ λ(x : <>) → λ(a : Type) → merge {} x : a │
└──────────────────────────────────────────┘
⇧
This should be ❰{=}❱ instead
|]
where
txt0 = Text.toStrict (Dhall.Core.pretty expr0)
txt1 = Text.toStrict (Dhall.Core.pretty expr1)
prettyTypeMessage (MustMergeUnion expr0 expr1) = ErrorMessages {..}
where
short = "❰merge❱ expects a union"
long =
Builder.fromText [NeatInterpolation.text|
Explanation: You can ❰merge❱ the alternatives of a union using a record with one
handler per alternative, like this:
┌─────────────────────────────────────────────────────────────────────┐
│ let union = < Left = +2 | Right : Bool > │
│ in let handlers = { Left = Natural/even, Right = λ(x : Bool) → x } │
│ in merge handlers union : Bool │
└─────────────────────────────────────────────────────────────────────┘
... but the second argument to ❰merge❱ must be a union and not some other type.
For example, the following expression is $_NOT valid:
┌──────────────────────────────────────────┐
│ let handlers = { Foo = λ(x : Bool) → x } │
│ in merge handlers True : True │
└──────────────────────────────────────────┘
⇧
Invalid: ❰True❱ isn't a union
You tried to ❰merge❱ this expression:
↳ $txt0
... which is not a union, but is actually a value of type:
↳ $txt1
|]
where
txt0 = Text.toStrict (Dhall.Core.pretty expr0)
txt1 = Text.toStrict (Dhall.Core.pretty expr1)
prettyTypeMessage (UnusedHandler ks) = ErrorMessages {..}
where
short = "Unused handler"
long =
Builder.fromText [NeatInterpolation.text|
Explanation: You can ❰merge❱ the alternatives of a union using a record with one
handler per alternative, like this:
┌─────────────────────────────────────────────────────────────────────┐
│ let union = < Left = +2 | Right : Bool > │
│ in let handlers = { Left = Natural/even, Right = λ(x : Bool) → x } │
│ in merge handlers union : Bool │
└─────────────────────────────────────────────────────────────────────┘
... but you must provide exactly one handler per alternative in the union. You
cannot supply extra handlers
For example, the following expression is $_NOT valid:
┌───────────────────────────────────────┐
│ let union = < Left = +2 > │ The ❰Right❱ alternative is missing
│ in let handlers = │
│ { Left = Natural/even │
│ , Right = λ(x : Bool) → x │ Invalid: ❰Right❱ handler isn't used
│ } │
│ in merge handlers union : Bool │
└───────────────────────────────────────┘
You provided the following handlers:
↳ $txt0
... which had no matching alternatives in the union you tried to ❰merge❱
|]
where
txt0 = Text.toStrict (Text.intercalate ", " (Data.Set.toList ks))
prettyTypeMessage (MissingHandler ks) = ErrorMessages {..}
where
short = "Missing handler"
long =
Builder.fromText [NeatInterpolation.text|
Explanation: You can ❰merge❱ the alternatives of a union using a record with one
handler per alternative, like this:
┌─────────────────────────────────────────────────────────────────────┐
│ let union = < Left = +2 | Right : Bool > │
│ in let handlers = { Left = Natural/even, Right = λ(x : Bool) → x } │
│ in merge handlers union : Bool │
└─────────────────────────────────────────────────────────────────────┘
... but you must provide exactly one handler per alternative in the union. You
cannot omit any handlers
For example, the following expression is $_NOT valid:
Invalid: Missing ❰Right❱ handler
⇩
┌─────────────────────────────────────────────────┐
│ let handlers = { Left = Natural/even } │
│ in let union = < Left = +2 | Right : Bool > │
│ in merge handlers union : Bool │
└─────────────────────────────────────────────────┘
Note that you need to provide handlers for other alternatives even if those
alternatives are never used
You need to supply the following handlers:
↳ $txt0
|]
where
txt0 = Text.toStrict (Text.intercalate ", " (Data.Set.toList ks))
prettyTypeMessage (HandlerInputTypeMismatch expr0 expr1 expr2) =
ErrorMessages {..}
where
short = "Wrong handler input type"
long =
Builder.fromText [NeatInterpolation.text|
Explanation: You can ❰merge❱ the alternatives of a union using a record with one
handler per alternative, like this:
┌─────────────────────────────────────────────────────────────────────┐
│ let union = < Left = +2 | Right : Bool > │
│ in let handlers = { Left = Natural/even, Right = λ(x : Bool) → x } │
│ in merge handlers union : Bool │
└─────────────────────────────────────────────────────────────────────┘
... as long as the input type of each handler function matches the type of the
corresponding alternative:
┌───────────────────────────────────────────────────────────┐
│ union : < Left : Natural | Right : Bool > │
└───────────────────────────────────────────────────────────┘
⇧ ⇧
These must match These must match
⇩ ⇩
┌───────────────────────────────────────────────────────────┐
│ handlers : { Left : Natural → Bool, Right : Bool → Bool } │
└───────────────────────────────────────────────────────────┘
For example, the following expression is $_NOT valid:
Invalid: Doesn't match the type of the ❰Right❱ alternative
⇩
┌──────────────────────────────────────────────────────────────────────┐
│ let handlers = { Left = Natural/even | Right = λ(x : Text) → x } │
│ in let union = < Left = +2 | Right : Bool > │
│ in merge handlers union : Bool │
└──────────────────────────────────────────────────────────────────────┘
Your handler for the following alternative:
↳ $txt0
... needs to accept an input value of type:
↳ $txt1
... but actually accepts an input value of a different type:
↳ $txt2
|]
where
txt0 = Text.toStrict (Dhall.Core.pretty expr0)
txt1 = Text.toStrict (Dhall.Core.pretty expr1)
txt2 = Text.toStrict (Dhall.Core.pretty expr2)
prettyTypeMessage (HandlerOutputTypeMismatch expr0 expr1 expr2) =
ErrorMessages {..}
where
short = "Wrong handler output type"
long =
Builder.fromText [NeatInterpolation.text|
Explanation: You can ❰merge❱ the alternatives of a union using a record with one
handler per alternative, like this:
┌─────────────────────────────────────────────────────────────────────┐
│ let union = < Left = +2 | Right : Bool > │
│ in let handlers = { Left = Natural/even, Right = λ(x : Bool) → x } │
│ in merge handlers union : Bool │
└─────────────────────────────────────────────────────────────────────┘
... as long as the output type of each handler function matches the declared type
of the result:
┌───────────────────────────────────────────────────────────┐
│ handlers : { Left : Natural → Bool, Right : Bool → Bool } │
└───────────────────────────────────────────────────────────┘
⇧ ⇧
These output types ...
... must match the declared type of the ❰merge❱
⇩
┌─────────────────────────────┐
│ merge handlers union : Bool │
└─────────────────────────────┘
For example, the following expression is $_NOT valid:
┌──────────────────────────────────────────────────────────────────────┐
│ let union = < Left = +2 | Right : Bool > │
│ in let handlers = { Left = Natural/even, Right = λ(x : Bool) → x } │
│ in merge handlers union : Text │
└──────────────────────────────────────────────────────────────────────┘
⇧
Invalid: Doesn't match output of either handler
Your handler for the following alternative:
↳ $txt0
... needs to return an output value of type:
↳ $txt1
... but actually returns an output value of a different type:
↳ $txt2
|]
where
txt0 = Text.toStrict (Dhall.Core.pretty expr0)
txt1 = Text.toStrict (Dhall.Core.pretty expr1)
txt2 = Text.toStrict (Dhall.Core.pretty expr2)
prettyTypeMessage (HandlerNotAFunction k expr0) = ErrorMessages {..}
where
short = "Handler is not a function"
long =
Builder.fromText [NeatInterpolation.text|
Explanation: You can ❰merge❱ the alternatives of a union using a record with one
handler per alternative, like this:
┌─────────────────────────────────────────────────────────────────────┐
│ let union = < Left = +2 | Right : Bool > │
│ in let handlers = { Left = Natural/even, Right = λ(x : Bool) → x } │
│ in merge handlers union : Bool │
└─────────────────────────────────────────────────────────────────────┘
... as long as each handler is a function
For example, the following expression is $_NOT valid:
┌─────────────────────────────────────────┐
│ merge { Foo = True } < Foo = 1 > : Bool │
└─────────────────────────────────────────┘
⇧
Invalid: Not a function
Your handler for this alternative:
↳ $txt0
... has the following type:
↳ $txt1
... which is not the type of a function
|]
where
txt0 = Text.toStrict (Dhall.Core.pretty k)
txt1 = Text.toStrict (Dhall.Core.pretty expr0)
prettyTypeMessage (NotARecord k expr0 expr1) = ErrorMessages {..}
where
short = "Not a record"
long =
Builder.fromText [NeatInterpolation.text|
Explanation: You can only access fields on records, like this:
┌─────────────────────────────────┐
│ { foo = True, bar = "ABC" }.foo │ This is valid ...
└─────────────────────────────────┘
┌───────────────────────────────────────────┐
│ λ(r : { foo : Bool, bar : Text }) → r.foo │ ... and so is this
└───────────────────────────────────────────┘
... but you cannot access fields on nonrecord expressions
For example, the following expression is $_NOT valid:
┌───────┐
│ 1.foo │
└───────┘
⇧
Invalid: Not a record
You tried to access a field named:
↳ $txt0
... on the following expression which is not a record:
↳ $txt1
... but is actually an expression of type:
↳ $txt2
Some common reasons why you might get this error:
● You accidentally try to access a field of a union instead of a record, like
this:
┌─────────────────┐
│ < foo : a >.foo │
└─────────────────┘
⇧
This is a union, not a record
|]
where
txt0 = Text.toStrict (Dhall.Core.pretty k )
txt1 = Text.toStrict (Dhall.Core.pretty expr0)
txt2 = Text.toStrict (Dhall.Core.pretty expr1)
prettyTypeMessage (MissingField k expr0) = ErrorMessages {..}
where
short = "Missing record field"
long =
Builder.fromText [NeatInterpolation.text|
Explanation: You can only access fields on records, like this:
┌─────────────────────────────────┐
│ { foo = True, bar = "ABC" }.foo │ This is valid ...
└─────────────────────────────────┘
┌───────────────────────────────────────────┐
│ λ(r : { foo : Bool, bar : Text }) → r.foo │ ... and so is this
└───────────────────────────────────────────┘
... but you can only access fields if they are present
For example, the following expression is $_NOT valid:
┌─────────────────────────────────┐
│ { foo = True, bar = "ABC" }.qux │
└─────────────────────────────────┘
⇧
Invalid: the record has no ❰qux❱ field
You tried to access a field named:
↳ $txt0
... but the field is missing because the record only defines the following fields:
↳ $txt1
|]
where
txt0 = Text.toStrict (Dhall.Core.pretty k )
txt1 = Text.toStrict (Dhall.Core.pretty expr0)
prettyTypeMessage (CantAnd expr0 expr1) =
buildBooleanOperator "&&" expr0 expr1
prettyTypeMessage (CantOr expr0 expr1) =
buildBooleanOperator "||" expr0 expr1
prettyTypeMessage (CantEQ expr0 expr1) =
buildBooleanOperator "==" expr0 expr1
prettyTypeMessage (CantNE expr0 expr1) =
buildBooleanOperator "/=" expr0 expr1
prettyTypeMessage (CantTextAppend expr0 expr1) = ErrorMessages {..}
where
short = "❰++❱ only works on ❰Text❱"
long =
Builder.fromText [NeatInterpolation.text|
Explanation: The ❰++❱ operator expects two arguments that have type ❰Text❱
For example, this is a valid use of ❰++❱:
┌────────────────┐
│ "ABC" ++ "DEF" │
└────────────────┘
You provided this argument:
↳ $txt0
... which does not have type ❰Text❱ but instead has type:
↳ $txt1
Some common reasons why you might get this error:
● You might have thought that ❰++❱ was the operator to combine two lists:
┌────────────────────────┐
│ [1, 2, 3] ++ [4, 5, 6] │ Not valid
└────────────────────────┘
The Dhall programming language does not provide a builtin operator for
combining two lists
|]
where
txt0 = Text.toStrict (Dhall.Core.pretty expr0)
txt1 = Text.toStrict (Dhall.Core.pretty expr1)
prettyTypeMessage (CantAdd expr0 expr1) =
buildNaturalOperator "+" expr0 expr1
prettyTypeMessage (CantMultiply expr0 expr1) =
buildNaturalOperator "*" expr0 expr1
prettyTypeMessage (NoDependentTypes expr0 expr1) = ErrorMessages {..}
where
short = "No dependent types"
long =
Builder.fromText [NeatInterpolation.text|
Explanation: The Dhall programming language does not allow functions from terms
to types. These function types are also known as "dependent function types"
because you have a type whose value "depends" on the value of a term.
For example, this is $_NOT a legal function type:
┌─────────────┐
│ Bool → Type │
└─────────────┘
Similarly, this is $_NOT legal code:
┌────────────────────────────────────────────────────┐
│ λ(Vector : Natural → Type → Type) → Vector +0 Text │
└────────────────────────────────────────────────────┘
⇧
Invalid dependent type
Your function type is invalid because the input has type:
↳ $txt0
... and the output has kind:
↳ $txt1
... which makes this a forbidden dependent function type
|]
where
txt0 = Text.toStrict (Dhall.Core.pretty expr0)
txt1 = Text.toStrict (Dhall.Core.pretty expr1)
prettyTypeMessage (NoDependentLet expr0 expr1) = ErrorMessages {..}
where
short = "No dependent ❰let❱"
long =
Builder.fromText [NeatInterpolation.text|
Explanation: The Dhall programming language does not allow ❰let❱ expressions
from terms to types. These ❰let❱ expressions are also known as "dependent ❰let❱
expressions" because you have a type whose value depends on the value of a term.
The Dhall language forbids these dependent ❰let❱ expressions in order to
guarantee that ❰let❱ expressions of the form:
┌────────────────────┐
│ let x : t = r in e │
└────────────────────┘
... are always equivalent to:
┌──────────────────┐
│ (λ(x : t) → e) r │
└──────────────────┘
This means that both expressions should normalize to the same result and if one
of the two fails to type check then the other should fail to type check, too.
For this reason, the following is $_NOT legal code:
┌───────────────────┐
│ let x = 2 in Text │
└───────────────────┘
... because the above ❰let❱ expression is equivalent to:
┌─────────────────────────────┐
│ let x : Integer = 2 in Text │
└─────────────────────────────┘
... which in turn must be equivalent to:
┌───────────────────────────┐
│ (λ(x : Integer) → Text) 2 │
└───────────────────────────┘
... which in turn fails to type check because this subexpression:
┌───────────────────────┐
│ λ(x : Integer) → Text │
└───────────────────────┘
... has type:
┌───────────────────────┐
│ ∀(x : Integer) → Text │
└───────────────────────┘
... which is a forbidden dependent function type (i.e. a function from a term to
a type). Therefore the equivalent ❰let❱ expression is also forbidden.
Your ❰let❱ expression is invalid because the input has type:
↳ $txt0
... and the output has kind:
↳ $txt1
... which makes this a forbidden dependent ❰let❱ expression
|]
where
txt0 = Text.toStrict (Dhall.Core.pretty expr0)
txt1 = Text.toStrict (Dhall.Core.pretty expr1)
buildBooleanOperator :: Text -> Expr s X -> Expr s X -> ErrorMessages
buildBooleanOperator operator expr0 expr1 = ErrorMessages {..}
where
short =
Builder.fromText
(Data.Text.strip
[NeatInterpolation.text|❰$txt2❱ only works on ❰Bool❱s|] )
long =
Builder.fromText [NeatInterpolation.text|
Explanation: The ❰$txt2❱ operator expects two arguments that have type ❰Bool❱
For example, this is a valid use of ❰$txt2❱:
┌───────────────┐
│ True $txt2 False │
└───────────────┘
You provided this argument:
↳ $txt0
... which does not have type ❰Bool❱ but instead has type:
↳ $txt1
|]
where
txt0 = Text.toStrict (Dhall.Core.pretty expr0)
txt1 = Text.toStrict (Dhall.Core.pretty expr1)
txt2 = Text.toStrict operator
buildNaturalOperator :: Text -> Expr s X -> Expr s X -> ErrorMessages
buildNaturalOperator operator expr0 expr1 = ErrorMessages {..}
where
short =
Builder.fromText
(Data.Text.strip
[NeatInterpolation.text|❰$txt2❱ only works on ❰Natural❱s|] )
long =
Builder.fromText [NeatInterpolation.text|
Explanation: The ❰$txt2❱ operator expects two arguments that have type ❰Natural❱
For example, this is a valid use of ❰$txt2❱:
┌─────────┐
│ +3 $txt2 +5 │
└─────────┘
You provided this argument:
↳ $txt0
... which does not have type ❰Natural❱ but instead has type:
↳ $txt1
Some common reasons why you might get this error:
● You might have tried to use an ❰Integer❱, which is $_NOT allowed:
┌─────────────────────────────────────────┐
│ λ(x : Integer) → λ(y : Integer) → x $txt2 y │ Not valid
└─────────────────────────────────────────┘
You can only use ❰Natural❱ numbers
● You might have mistakenly used an ❰Integer❱ literal, which is $_NOT allowed:
┌───────┐
│ 2 $txt2 2 │ Not valid
└───────┘
You need to prefix each literal with a ❰+❱ to transform them into ❰Natural❱
literals, like this:
┌─────────┐
│ +2 $txt2 +2 │ Valid
└─────────┘
|]
where
txt0 = Text.toStrict (Dhall.Core.pretty expr0)
txt1 = Text.toStrict (Dhall.Core.pretty expr1)
txt2 = Text.toStrict operator
data TypeError s = TypeError
{ context :: Context (Expr s X)
, current :: Expr s X
, typeMessage :: TypeMessage s
} deriving (Typeable)
instance Buildable s => Show (TypeError s) where
show = Text.unpack . Dhall.Core.pretty
instance (Buildable s, Typeable s) => Exception (TypeError s)
instance Buildable s => Buildable (TypeError s) where
build (TypeError ctx expr msg)
= "\n"
<> ( if Text.null (Builder.toLazyText (buildContext ctx))
then ""
else buildContext ctx <> "\n"
)
<> shortTypeMessage msg <> "\n"
<> source
where
buildKV (key, val) = build key <> " : " <> build val
buildContext =
build
. Text.unlines
. map (Builder.toLazyText . buildKV)
. reverse
. Dhall.Context.toList
source = case expr of
Note s _ -> build s
_ -> mempty
newtype DetailedTypeError s = DetailedTypeError (TypeError s)
deriving (Typeable)
instance Buildable s => Show (DetailedTypeError s) where
show = Text.unpack . Dhall.Core.pretty
instance (Buildable s, Typeable s) => Exception (DetailedTypeError s)
instance Buildable s => Buildable (DetailedTypeError s) where
build (DetailedTypeError (TypeError ctx expr msg))
= "\n"
<> ( if Text.null (Builder.toLazyText (buildContext ctx))
then ""
else buildContext ctx <> "\n"
)
<> longTypeMessage msg <> "\n"
<> "────────────────────────────────────────────────────────────────────────────────\n"
<> "\n"
<> source
where
buildKV (key, val) = build key <> " : " <> build val
buildContext =
build
. Text.unlines
. map (Builder.toLazyText . buildKV)
. reverse
. Dhall.Context.toList
source = case expr of
Note s _ -> build s
_ -> mempty