{-# LANGUAGE ConstraintKinds #-}
{-# LANGUAGE CPP #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE InstanceSigs #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE Trustworthy #-}
module Generic.Data.Internal.Read where
import Data.Coerce
import Data.Functor.Classes (Read1(..))
import Data.Functor.Identity
import Data.Proxy
import Generic.Data.Internal.Utils (isSymDataCon, isSymVar)
import GHC.Generics hiding (prec)
import GHC.Read (expectP, list)
import GHC.Show (appPrec, appPrec1)
import Text.ParserCombinators.ReadPrec
import Text.Read (Read(..), parens)
import Text.Read.Lex (Lexeme(..))
greadPrec :: (Generic a, GRead0 (Rep a)) => ReadPrec a
greadPrec :: forall a. (Generic a, GRead0 (Rep a)) => ReadPrec a
greadPrec = forall a x. Generic a => Rep a x -> a
to forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
<$> forall (p :: * -> *) (f :: * -> *) a.
GRead p f =>
p (ReadPrec a, ReadPrec [a]) -> ReadPrec (f a)
gPrecRead forall {k} (t :: k). Proxy t
Proxy
type GRead0 = GRead Proxy
gliftReadPrec
:: (Generic1 f, GRead1 (Rep1 f))
=> ReadPrec a -> ReadPrec [a]
-> ReadPrec (f a)
gliftReadPrec :: forall (f :: * -> *) a.
(Generic1 f, GRead1 (Rep1 f)) =>
ReadPrec a -> ReadPrec [a] -> ReadPrec (f a)
gliftReadPrec ReadPrec a
readPrec' ReadPrec [a]
readList' =
forall k (f :: k -> *) (a :: k). Generic1 f => Rep1 f a -> f a
to1 forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
<$> forall (p :: * -> *) (f :: * -> *) a.
GRead p f =>
p (ReadPrec a, ReadPrec [a]) -> ReadPrec (f a)
gPrecRead (forall a. a -> Identity a
Identity (ReadPrec a
readPrec', ReadPrec [a]
readList'))
type GRead1 = GRead Identity
class GRead p f where
gPrecRead :: p (ReadPrec a, ReadPrec [a]) -> ReadPrec (f a)
instance (GRead p f, IsNullaryDataType f) => GRead p (M1 D d f) where
gPrecRead :: forall a. p (ReadPrec a, ReadPrec [a]) -> ReadPrec (M1 D d f a)
gPrecRead p (ReadPrec a, ReadPrec [a])
p = forall (f :: * -> *) p i (c :: Meta).
ReadPrec (f p) -> ReadPrec (M1 i c f p)
coerceM1 (forall a. ReadPrec a -> ReadPrec a
parensIfNonNullary (forall (p :: * -> *) (f :: * -> *) a.
GRead p f =>
p (ReadPrec a, ReadPrec [a]) -> ReadPrec (f a)
gPrecRead p (ReadPrec a, ReadPrec [a])
p))
where
x :: f a
x :: forall a. f a
x = forall a. HasCallStack => a
undefined
parensIfNonNullary :: ReadPrec a -> ReadPrec a
parensIfNonNullary :: forall a. ReadPrec a -> ReadPrec a
parensIfNonNullary = if forall (f :: * -> *) a. IsNullaryDataType f => f a -> Bool
isNullaryDataType forall a. f a
x
then forall a. a -> a
id
else forall a. ReadPrec a -> ReadPrec a
parens
instance (GRead p f, GRead p g) => GRead p (f :+: g) where
gPrecRead :: forall a. p (ReadPrec a, ReadPrec [a]) -> ReadPrec ((:+:) f g a)
gPrecRead p (ReadPrec a, ReadPrec [a])
p = forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap forall k (f :: k -> *) (g :: k -> *) (p :: k). f p -> (:+:) f g p
L1 (forall (p :: * -> *) (f :: * -> *) a.
GRead p f =>
p (ReadPrec a, ReadPrec [a]) -> ReadPrec (f a)
gPrecRead p (ReadPrec a, ReadPrec [a])
p) forall a. ReadPrec a -> ReadPrec a -> ReadPrec a
+++ forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap forall k (f :: k -> *) (g :: k -> *) (p :: k). g p -> (:+:) f g p
R1 (forall (p :: * -> *) (f :: * -> *) a.
GRead p f =>
p (ReadPrec a, ReadPrec [a]) -> ReadPrec (f a)
gPrecRead p (ReadPrec a, ReadPrec [a])
p)
instance (Constructor c, GReadC p c f) => GRead p (M1 C c f) where
gPrecRead :: forall a. p (ReadPrec a, ReadPrec [a]) -> ReadPrec (M1 C c f a)
gPrecRead p (ReadPrec a, ReadPrec [a])
p = forall (p :: * -> *) (c :: Meta) (f :: * -> *) a.
GReadC p c f =>
p (ReadPrec a, ReadPrec [a])
-> String -> Fixity -> ReadPrec (M1 C c f a)
gPrecReadC p (ReadPrec a, ReadPrec [a])
p (forall {k} (c :: k) k1 (t :: k -> (k1 -> *) -> k1 -> *)
(f :: k1 -> *) (a :: k1).
Constructor c =>
t c f a -> String
conName forall a. M1 C c f a
x) (forall {k} (c :: k) k1 (t :: k -> (k1 -> *) -> k1 -> *)
(f :: k1 -> *) (a :: k1).
Constructor c =>
t c f a -> Fixity
conFixity forall a. M1 C c f a
x)
where
x :: M1 C c f a
x :: forall a. M1 C c f a
x = forall a. HasCallStack => a
undefined
instance GRead p V1 where
gPrecRead :: forall a. p (ReadPrec a, ReadPrec [a]) -> ReadPrec (V1 a)
gPrecRead p (ReadPrec a, ReadPrec [a])
_ = forall a. ReadPrec a
pfail
class IsNullaryDataType f where
isNullaryDataType :: f a -> Bool
instance IsNullaryDataType (f :+: g) where
isNullaryDataType :: forall a. (:+:) f g a -> Bool
isNullaryDataType (:+:) f g a
_ = Bool
False
instance IsNullaryDataType (C1 c f) where
isNullaryDataType :: forall a. C1 c f a -> Bool
isNullaryDataType C1 c f a
_ = Bool
False
instance IsNullaryDataType V1 where
isNullaryDataType :: forall a. V1 a -> Bool
isNullaryDataType V1 a
_ = Bool
True
class GReadC p c f where
gPrecReadC :: p (ReadPrec a, ReadPrec [a]) -> String -> Fixity -> ReadPrec (M1 C c f a)
instance GReadFields p f => GReadC p ('MetaCons s y 'False) f where
gPrecReadC :: forall a. p (ReadPrec a, ReadPrec [a]) -> String -> Fixity
-> ReadPrec (M1 C ('MetaCons s y 'False) f a)
gPrecReadC :: forall a.
p (ReadPrec a, ReadPrec [a])
-> String -> Fixity -> ReadPrec (M1 C ('MetaCons s y 'False) f a)
gPrecReadC p (ReadPrec a, ReadPrec [a])
p String
name Fixity
fixity
| Infix Associativity
_ Int
fy <- Fixity
fixity, Branch ReadPrecTree (f a)
k1 ReadPrecTree (g a)
k2 <- ReadPrecTree (f a)
fields
= forall (f :: * -> *) p i (c :: Meta).
ReadPrec (f p) -> ReadPrec (M1 i c f p)
coerceM1 forall a b. (a -> b) -> a -> b
$ forall a. Int -> ReadPrec a -> ReadPrec a
prec Int
fy forall a b. (a -> b) -> a -> b
$ do
f a
k1' <- forall a. ReadPrecTree a -> ReadPrec a
toReadPrec ReadPrecTree (f a)
k1
if String -> Bool
isSymDataCon String
name
then Lexeme -> ReadPrec ()
expectP (String -> Lexeme
Symbol String
name)
else forall (t :: * -> *) (m :: * -> *) a b.
(Foldable t, Monad m) =>
(a -> m b) -> t a -> m ()
mapM_ Lexeme -> ReadPrec ()
expectP ([String -> Lexeme
Punc String
"`"] forall a. [a] -> [a] -> [a]
++ String -> [Lexeme]
identHLexemes String
name forall a. [a] -> [a] -> [a]
++ [String -> Lexeme
Punc String
"`"])
g a
k2' <- forall a. ReadPrecTree a -> ReadPrec a
toReadPrec ReadPrecTree (g a)
k2
forall (f :: * -> *) a. Applicative f => a -> f a
pure (f a
k1' forall k (f :: k -> *) (g :: k -> *) (p :: k).
f p -> g p -> (:*:) f g p
:*: g a
k2')
| Bool
otherwise
= forall (f :: * -> *) p i (c :: Meta).
ReadPrec (f p) -> ReadPrec (M1 i c f p)
coerceM1 forall a b. (a -> b) -> a -> b
$ forall a. Int -> ReadPrec a -> ReadPrec a
prec Int
appPrec forall a b. (a -> b) -> a -> b
$ do
String -> ReadPrec ()
readPrefixCon String
name
forall a. ReadPrecTree a -> ReadPrec a
toReadPrec ReadPrecTree (f a)
fields
where
fields :: ReadPrecTree (f a)
fields :: ReadPrecTree (f a)
fields = forall (p :: * -> *) (f :: * -> *) a.
GReadFields p f =>
p (ReadPrec a, ReadPrec [a]) -> ReadPrecTree (f a)
gPrecReadFields p (ReadPrec a, ReadPrec [a])
p
instance GReadNamed p f => GReadC p ('MetaCons s y 'True) f where
gPrecReadC :: forall a.
p (ReadPrec a, ReadPrec [a])
-> String -> Fixity -> ReadPrec (M1 C ('MetaCons s y 'True) f a)
gPrecReadC p (ReadPrec a, ReadPrec [a])
p String
name Fixity
_fixity = forall (f :: * -> *) p i (c :: Meta).
ReadPrec (f p) -> ReadPrec (M1 i c f p)
coerceM1 forall a b. (a -> b) -> a -> b
$ forall a. Int -> ReadPrec a -> ReadPrec a
prec Int
appPrec1 forall a b. (a -> b) -> a -> b
$ do
String -> ReadPrec ()
readPrefixCon String
name
forall a. Char -> ReadPrec a -> Char -> ReadPrec a
readSurround Char
'{' ReadPrec (f a)
fields Char
'}'
where
fields :: ReadPrec (f a)
fields = forall (p :: * -> *) (f :: * -> *) a.
GReadNamed p f =>
p (ReadPrec a, ReadPrec [a]) -> ReadPrec (f a)
gPrecReadNamed p (ReadPrec a, ReadPrec [a])
p
class GReadFields p f where
gPrecReadFields :: p (ReadPrec a, ReadPrec [a]) -> ReadPrecTree (f a)
instance (GReadFields p f, GReadFields p g) => GReadFields p (f :*: g) where
gPrecReadFields :: forall a.
p (ReadPrec a, ReadPrec [a]) -> ReadPrecTree ((:*:) f g a)
gPrecReadFields p (ReadPrec a, ReadPrec [a])
p = forall (a :: * -> *) a (i :: * -> *).
ReadPrecTree (a a)
-> ReadPrecTree (i a) -> ReadPrecTree ((:*:) a i a)
Branch (forall (p :: * -> *) (f :: * -> *) a.
GReadFields p f =>
p (ReadPrec a, ReadPrec [a]) -> ReadPrecTree (f a)
gPrecReadFields p (ReadPrec a, ReadPrec [a])
p) (forall (p :: * -> *) (f :: * -> *) a.
GReadFields p f =>
p (ReadPrec a, ReadPrec [a]) -> ReadPrecTree (f a)
gPrecReadFields p (ReadPrec a, ReadPrec [a])
p)
instance GReadSingle p f => GReadFields p (M1 S c f) where
gPrecReadFields :: forall a. p (ReadPrec a, ReadPrec [a]) -> ReadPrecTree (M1 S c f a)
gPrecReadFields p (ReadPrec a, ReadPrec [a])
p = forall (a :: * -> *) a i (c :: Meta).
ReadPrec (a a) -> ReadPrecTree (M1 i c a a)
M1Leaf (forall a. ReadPrec a -> ReadPrec a
step (forall (p :: * -> *) (f :: * -> *) a.
GReadSingle p f =>
p (ReadPrec a, ReadPrec [a]) -> ReadPrec (f a)
gPrecReadSingle p (ReadPrec a, ReadPrec [a])
p))
instance GReadFields p U1 where
gPrecReadFields :: forall a. p (ReadPrec a, ReadPrec [a]) -> ReadPrecTree (U1 a)
gPrecReadFields p (ReadPrec a, ReadPrec [a])
_ = forall a. ReadPrecTree (U1 a)
U1Leaf
class GReadNamed p f where
gPrecReadNamed :: p (ReadPrec a, ReadPrec [a]) -> ReadPrec (f a)
instance (GReadNamed p f, GReadNamed p g) => GReadNamed p (f :*: g) where
gPrecReadNamed :: forall a. p (ReadPrec a, ReadPrec [a]) -> ReadPrec ((:*:) f g a)
gPrecReadNamed p (ReadPrec a, ReadPrec [a])
p = do
f a
l <- forall (p :: * -> *) (f :: * -> *) a.
GReadNamed p f =>
p (ReadPrec a, ReadPrec [a]) -> ReadPrec (f a)
gPrecReadNamed p (ReadPrec a, ReadPrec [a])
p
Lexeme -> ReadPrec ()
expectP (String -> Lexeme
Punc String
",")
g a
r <- forall (p :: * -> *) (f :: * -> *) a.
GReadNamed p f =>
p (ReadPrec a, ReadPrec [a]) -> ReadPrec (f a)
gPrecReadNamed p (ReadPrec a, ReadPrec [a])
p
forall (f :: * -> *) a. Applicative f => a -> f a
pure (f a
l forall k (f :: k -> *) (g :: k -> *) (p :: k).
f p -> g p -> (:*:) f g p
:*: g a
r)
instance (Selector c, GReadSingle p f) => GReadNamed p (M1 S c f) where
gPrecReadNamed :: forall a. p (ReadPrec a, ReadPrec [a]) -> ReadPrec (M1 S c f a)
gPrecReadNamed p (ReadPrec a, ReadPrec [a])
p = forall (f :: * -> *) p i (c :: Meta).
ReadPrec (f p) -> ReadPrec (M1 i c f p)
coerceM1 forall a b. (a -> b) -> a -> b
$ do
forall (t :: * -> *) (m :: * -> *) a b.
(Foldable t, Monad m) =>
(a -> m b) -> t a -> m ()
mapM_ Lexeme -> ReadPrec ()
expectP [Lexeme]
snameLexemes
Lexeme -> ReadPrec ()
expectP (String -> Lexeme
Punc String
"=")
forall a. ReadPrec a -> ReadPrec a
reset (forall (p :: * -> *) (f :: * -> *) a.
GReadSingle p f =>
p (ReadPrec a, ReadPrec [a]) -> ReadPrec (f a)
gPrecReadSingle p (ReadPrec a, ReadPrec [a])
p)
where
x :: M1 S c f a
x :: forall a. M1 S c f a
x = forall a. HasCallStack => a
undefined
sname :: String
sname :: String
sname = forall {k} (s :: k) k1 (t :: k -> (k1 -> *) -> k1 -> *)
(f :: k1 -> *) (a :: k1).
Selector s =>
t s f a -> String
selName forall a. M1 S c f a
x
snameLexemes :: [Lexeme]
snameLexemes :: [Lexeme]
snameLexemes | String -> Bool
isSymVar String
sname
= [String -> Lexeme
Punc String
"(", String -> Lexeme
Symbol String
sname, String -> Lexeme
Punc String
")"]
| Bool
otherwise
= String -> [Lexeme]
identHLexemes String
sname
instance GReadNamed p U1 where
gPrecReadNamed :: forall a. p (ReadPrec a, ReadPrec [a]) -> ReadPrec (U1 a)
gPrecReadNamed p (ReadPrec a, ReadPrec [a])
_ = forall (f :: * -> *) a. Applicative f => a -> f a
pure forall k (p :: k). U1 p
U1
class GReadSingle p f where
gPrecReadSingle :: p (ReadPrec a, ReadPrec [a]) -> ReadPrec (f a)
instance Read a => GReadSingle p (K1 i a) where
gPrecReadSingle :: forall a. p (ReadPrec a, ReadPrec [a]) -> ReadPrec (K1 i a a)
gPrecReadSingle p (ReadPrec a, ReadPrec [a])
_ = forall x. ReadPrec a -> ReadPrec (K1 i a x)
coerceK1 forall a. Read a => ReadPrec a
readPrec
where
coerceK1 :: ReadPrec a -> ReadPrec (K1 i a x)
coerceK1 :: forall x. ReadPrec a -> ReadPrec (K1 i a x)
coerceK1 = coerce :: forall a b. Coercible a b => a -> b
coerce
instance Read1 f => GReadSingle Identity (Rec1 f) where
gPrecReadSingle :: forall a.
Identity (ReadPrec a, ReadPrec [a]) -> ReadPrec (Rec1 f a)
gPrecReadSingle (Identity (ReadPrec a, ReadPrec [a])
p) = forall a. ReadPrec (f a) -> ReadPrec (Rec1 f a)
coerceRec1 (forall (f :: * -> *) a.
Read1 f =>
(ReadPrec a, ReadPrec [a]) -> ReadPrec (f a)
liftReadPrecCompat (ReadPrec a, ReadPrec [a])
p)
where
coerceRec1 :: ReadPrec (f a) -> ReadPrec (Rec1 f a)
coerceRec1 :: forall a. ReadPrec (f a) -> ReadPrec (Rec1 f a)
coerceRec1 = coerce :: forall a b. Coercible a b => a -> b
coerce
instance GReadSingle Identity Par1 where
gPrecReadSingle :: forall a. Identity (ReadPrec a, ReadPrec [a]) -> ReadPrec (Par1 a)
gPrecReadSingle (Identity (ReadPrec a
readPrec', ReadPrec [a]
_)) = forall p. ReadPrec p -> ReadPrec (Par1 p)
coercePar1 ReadPrec a
readPrec'
where
coercePar1 :: ReadPrec p -> ReadPrec (Par1 p)
coercePar1 :: forall p. ReadPrec p -> ReadPrec (Par1 p)
coercePar1 = coerce :: forall a b. Coercible a b => a -> b
coerce
instance (Read1 f, GReadSingle p g) => GReadSingle p (f :.: g) where
gPrecReadSingle :: forall a. p (ReadPrec a, ReadPrec [a]) -> ReadPrec ((f :.: g) a)
gPrecReadSingle :: forall a. p (ReadPrec a, ReadPrec [a]) -> ReadPrec ((:.:) f g a)
gPrecReadSingle p (ReadPrec a, ReadPrec [a])
p = ReadPrec (f (g a)) -> ReadPrec ((:.:) f g a)
coerceComp1 (forall (f :: * -> *) a.
Read1 f =>
(ReadPrec a, ReadPrec [a]) -> ReadPrec (f a)
liftReadPrecCompat (ReadPrec (g a)
readPrec_, ReadPrec [g a]
readList_))
where
readPrec_ :: ReadPrec (g a)
readPrec_ :: ReadPrec (g a)
readPrec_ = forall (p :: * -> *) (f :: * -> *) a.
GReadSingle p f =>
p (ReadPrec a, ReadPrec [a]) -> ReadPrec (f a)
gPrecReadSingle p (ReadPrec a, ReadPrec [a])
p
readList_ :: ReadPrec [g a]
readList_ :: ReadPrec [g a]
readList_ = forall a. ReadPrec a -> ReadPrec [a]
list ReadPrec (g a)
readPrec_
coerceComp1 :: ReadPrec (f (g a)) -> ReadPrec ((f :.: g) a)
coerceComp1 :: ReadPrec (f (g a)) -> ReadPrec ((:.:) f g a)
coerceComp1 = coerce :: forall a b. Coercible a b => a -> b
coerce
coerceM1 :: ReadPrec (f p) -> ReadPrec (M1 i c f p)
coerceM1 :: forall (f :: * -> *) p i (c :: Meta).
ReadPrec (f p) -> ReadPrec (M1 i c f p)
coerceM1 = coerce :: forall a b. Coercible a b => a -> b
coerce
liftReadPrecCompat :: Read1 f => (ReadPrec a, ReadPrec [a]) -> ReadPrec (f a)
liftReadPrecCompat :: forall (f :: * -> *) a.
Read1 f =>
(ReadPrec a, ReadPrec [a]) -> ReadPrec (f a)
liftReadPrecCompat (ReadPrec a
readPrec', ReadPrec [a]
readList') =
#if MIN_VERSION_base(4,10,0)
forall (f :: * -> *) a.
Read1 f =>
ReadPrec a -> ReadPrec [a] -> ReadPrec (f a)
liftReadPrec ReadPrec a
readPrec' ReadPrec [a]
readList'
#else
readS_to_Prec (liftReadsPrec (readPrec_to_S readPrec')
(readPrec_to_S readList' 0))
#endif
data ReadPrecTree a where
U1Leaf :: ReadPrecTree (U1 a)
M1Leaf :: ReadPrec (f a) -> ReadPrecTree (M1 i c f a)
Branch :: ReadPrecTree (f a) -> ReadPrecTree (g a) -> ReadPrecTree ((f :*: g) a)
toReadPrec :: ReadPrecTree a -> ReadPrec a
toReadPrec :: forall a. ReadPrecTree a -> ReadPrec a
toReadPrec ReadPrecTree a
U1Leaf = forall (f :: * -> *) a. Applicative f => a -> f a
pure forall k (p :: k). U1 p
U1
toReadPrec (M1Leaf ReadPrec (f a)
f) = forall (f :: * -> *) p i (c :: Meta).
ReadPrec (f p) -> ReadPrec (M1 i c f p)
coerceM1 ReadPrec (f a)
f
toReadPrec (Branch ReadPrecTree (f a)
f ReadPrecTree (g a)
g) = forall k (f :: k -> *) (g :: k -> *) (p :: k).
f p -> g p -> (:*:) f g p
(:*:) forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
<$> forall a. ReadPrecTree a -> ReadPrec a
toReadPrec ReadPrecTree (f a)
f forall (f :: * -> *) a b. Applicative f => f (a -> b) -> f a -> f b
<*> forall a. ReadPrecTree a -> ReadPrec a
toReadPrec ReadPrecTree (g a)
g
identHLexemes :: String -> [Lexeme]
identHLexemes :: String -> [Lexeme]
identHLexemes String
s | Just (String
ss, Char
'#') <- forall a. [a] -> Maybe ([a], a)
snocView String
s = [String -> Lexeme
Ident String
ss, String -> Lexeme
Symbol String
"#"]
| Bool
otherwise = [String -> Lexeme
Ident String
s]
readPrefixCon :: String -> ReadPrec ()
readPrefixCon :: String -> ReadPrec ()
readPrefixCon String
name
| String -> Bool
isSymDataCon String
name
= forall a. Char -> ReadPrec a -> Char -> ReadPrec a
readSurround Char
'(' (Lexeme -> ReadPrec ()
expectP (String -> Lexeme
Symbol String
name)) Char
')'
| Bool
otherwise
= forall (t :: * -> *) (m :: * -> *) a b.
(Foldable t, Monad m) =>
(a -> m b) -> t a -> m ()
mapM_ Lexeme -> ReadPrec ()
expectP (String -> [Lexeme]
identHLexemes String
name)
readSurround :: Char -> ReadPrec a -> Char -> ReadPrec a
readSurround :: forall a. Char -> ReadPrec a -> Char -> ReadPrec a
readSurround Char
c1 ReadPrec a
r Char
c2 = do
Lexeme -> ReadPrec ()
expectP (String -> Lexeme
Punc [Char
c1])
a
r' <- ReadPrec a
r
Lexeme -> ReadPrec ()
expectP (String -> Lexeme
Punc [Char
c2])
forall (f :: * -> *) a. Applicative f => a -> f a
pure a
r'
snocView :: [a] -> Maybe ([a], a)
snocView :: forall a. [a] -> Maybe ([a], a)
snocView [] = forall a. Maybe a
Nothing
snocView [a]
xs = forall {a}. [a] -> [a] -> Maybe ([a], a)
go [] [a]
xs
where
go :: [a] -> [a] -> Maybe ([a], a)
go [a]
acc [a
a] = forall a. a -> Maybe a
Just (forall a. [a] -> [a]
reverse [a]
acc, a
a)
go [a]
acc (a
a:[a]
as) = [a] -> [a] -> Maybe ([a], a)
go (a
aforall a. a -> [a] -> [a]
:[a]
acc) [a]
as
go [a]
_ [] = forall a. HasCallStack => String -> a
error String
"Util: snocView"