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diff --git a/users/Profpatsch/my-prelude/src/MyPrelude.hs b/users/Profpatsch/my-prelude/src/MyPrelude.hs new file mode 100644 index 000000000000..880983c47e92 --- /dev/null +++ b/users/Profpatsch/my-prelude/src/MyPrelude.hs @@ -0,0 +1,776 @@ +{-# LANGUAGE ImplicitParams #-} +{-# LANGUAGE LambdaCase #-} +{-# LANGUAGE MagicHash #-} +{-# LANGUAGE ViewPatterns #-} + +module MyPrelude + ( -- * Text conversions + Text, + ByteString, + Word8, + fmt, + textToString, + stringToText, + stringToBytesUtf8, + showToText, + textToBytesUtf8, + textToBytesUtf8Lazy, + bytesToTextUtf8, + bytesToTextUtf8Lazy, + bytesToTextUtf8Lenient, + bytesToTextUtf8LenientLazy, + bytesToTextUtf8Unsafe, + bytesToTextUtf8UnsafeLazy, + toStrict, + toLazy, + toStrictBytes, + toLazyBytes, + charToWordUnsafe, + + -- * IO + putStrLn, + putStderrLn, + exitWithMessage, + + -- * WIP code + todo, + + -- * Records + HasField, + + -- * Control flow + doAs, + (&), + (<&>), + (<|>), + foldMap1, + foldMap', + join, + when, + unless, + guard, + ExceptT (..), + runExceptT, + MonadThrow, + throwM, + MonadIO, + liftIO, + MonadReader, + asks, + Bifunctor, + first, + second, + bimap, + both, + foldMap, + fold, + foldl', + fromMaybe, + mapMaybe, + findMaybe, + Traversable, + for, + for_, + traverse, + traverse_, + traverseFold, + traverseFold1, + traverseFoldDefault, + MonadTrans, + lift, + + -- * Data types + Coercible, + coerce, + Proxy (Proxy), + Map, + annotate, + Validation (Success, Failure), + failure, + successes, + failures, + traverseValidate, + traverseValidateM, + traverseValidateM_, + eitherToValidation, + eitherToListValidation, + validationToEither, + These (This, That, These), + eitherToThese, + eitherToListThese, + validationToThese, + thenThese, + thenValidate, + thenValidateM, + NonEmpty ((:|)), + pattern IsEmpty, + pattern IsNonEmpty, + singleton, + nonEmpty, + nonEmptyDef, + overNonEmpty, + zipNonEmpty, + zipWithNonEmpty, + zip3NonEmpty, + zipWith3NonEmpty, + zip4NonEmpty, + toList, + lengthNatural, + maximum1, + minimum1, + maximumBy1, + minimumBy1, + Vector, + Generic, + Lift, + Semigroup, + sconcat, + Monoid, + mconcat, + ifTrue, + ifExists, + Void, + absurd, + Identity (Identity, runIdentity), + Natural, + intToNatural, + Scientific, + Contravariant, + contramap, + (>$<), + (>&<), + Profunctor, + dimap, + lmap, + rmap, + Semigroupoid, + Category, + (>>>), + (&>>), + Any, + + -- * Enum definition + inverseFunction, + inverseMap, + enumerateAll, + + -- * Map helpers + mapFromListOn, + mapFromListOnMerge, + + -- * Error handling + HasCallStack, + module Data.Error, + ) +where + +import Control.Applicative ((<|>)) +import Control.Category (Category, (>>>)) +import Control.Foldl.NonEmpty qualified as Foldl1 +import Control.Monad (guard, join, unless, when) +import Control.Monad.Catch (MonadThrow (throwM)) +import Control.Monad.Except + ( ExceptT (..), + runExceptT, + ) +import Control.Monad.IO.Class (MonadIO, liftIO) +import Control.Monad.Identity (Identity (Identity)) +import Control.Monad.Reader (MonadReader, asks) +import Control.Monad.Trans (MonadTrans (lift)) +import Data.Bifunctor (Bifunctor, bimap, first, second) +import Data.ByteString + ( ByteString, + ) +import Data.ByteString.Lazy qualified +import Data.Char qualified +import Data.Coerce (Coercible, coerce) +import Data.Data (Proxy (Proxy)) +import Data.Error +import Data.Foldable (Foldable (foldMap', toList), fold, foldl', for_, sequenceA_, traverse_) +import Data.Foldable qualified as Foldable +import Data.Function ((&)) +import Data.Functor ((<&>)) +import Data.Functor.Contravariant (Contravariant (contramap), (>$<)) +import Data.Functor.Identity (Identity (runIdentity)) +import Data.List (zip4) +import Data.List.NonEmpty (NonEmpty ((:|)), nonEmpty) +import Data.List.NonEmpty qualified as NonEmpty +import Data.Map.Strict + ( Map, + ) +import Data.Map.Strict qualified as Map +import Data.Maybe (fromMaybe, mapMaybe) +import Data.Maybe qualified as Maybe +import Data.Profunctor (Profunctor, dimap, lmap, rmap) +import Data.Scientific (Scientific) +import Data.Semigroup (sconcat) +import Data.Semigroup.Foldable (Foldable1 (fold1), foldMap1) +import Data.Semigroup.Traversable (Traversable1) +import Data.Semigroupoid (Semigroupoid (o)) +import Data.Text + ( Text, + ) +import Data.Text qualified +import Data.Text.Encoding qualified +import Data.Text.Encoding.Error qualified +import Data.Text.Lazy qualified +import Data.Text.Lazy.Encoding qualified +import Data.These (These (That, These, This)) +import Data.Traversable (for) +import Data.Vector (Vector) +import Data.Void (Void, absurd) +import Data.Word (Word8) +import GHC.Exception (errorCallWithCallStackException) +import GHC.Exts (Any, RuntimeRep, TYPE, raise#) +import GHC.Generics (Generic) +import GHC.Natural (Natural) +import GHC.Records (HasField) +import GHC.Stack (HasCallStack) +import GHC.Utils.Encoding qualified as GHC +import Language.Haskell.TH.Syntax (Lift) +import PyF (fmt) +import System.Exit qualified +import System.IO qualified +import Validation + ( Validation (Failure, Success), + eitherToValidation, + failure, + failures, + successes, + validationToEither, + ) + +-- | Mark a `do`-block with the type of the Monad/Applicativ it uses. +-- Only intended for reading ease and making code easier to understand, +-- especially do-blocks that use unconventional monads (like Maybe or List). +-- +-- Example: +-- +-- @ +-- doAs @Maybe $ do +-- a <- Just 'a' +-- b <- Just 'b' +-- pure (a, b) +-- @ +doAs :: forall m a. m a -> m a +doAs = id + +-- | Forward-applying 'contramap', like '&'/'$' and '<&>'/'<$>' but for '>$<'. +(>&<) :: (Contravariant f) => f b -> (a -> b) -> f a +(>&<) = flip contramap + +infixl 5 >&< + +-- | Forward semigroupoid application. The same as '(>>>)', but 'Semigroupoid' is not a superclass of 'Category' (yet). +-- +-- Specialized examples: +-- +-- @ +-- for functions : (a -> b) -> (b -> c) -> (a -> c) +-- for Folds: Fold a b -> Fold b c -> Fold a c +-- @ +(&>>) :: (Semigroupoid s) => s a b -> s b c -> s a c +(&>>) = flip Data.Semigroupoid.o + +-- like >>> +infixr 1 &>> + +-- | encode a Text to a UTF-8 encoded Bytestring +textToBytesUtf8 :: Text -> ByteString +textToBytesUtf8 = Data.Text.Encoding.encodeUtf8 + +-- | encode a lazy Text to a UTF-8 encoded lazy Bytestring +textToBytesUtf8Lazy :: Data.Text.Lazy.Text -> Data.ByteString.Lazy.ByteString +textToBytesUtf8Lazy = Data.Text.Lazy.Encoding.encodeUtf8 + +bytesToTextUtf8 :: ByteString -> Either Error Text +bytesToTextUtf8 = first exceptionToError . Data.Text.Encoding.decodeUtf8' + +bytesToTextUtf8Lazy :: Data.ByteString.Lazy.ByteString -> Either Error Data.Text.Lazy.Text +bytesToTextUtf8Lazy = first exceptionToError . Data.Text.Lazy.Encoding.decodeUtf8' + +-- | decode a Text from a ByteString that is assumed to be UTF-8 (crash if that is not the case) +bytesToTextUtf8Unsafe :: ByteString -> Text +bytesToTextUtf8Unsafe = Data.Text.Encoding.decodeUtf8 + +-- | decode a Text from a ByteString that is assumed to be UTF-8 (crash if that is not the case) +bytesToTextUtf8UnsafeLazy :: Data.ByteString.Lazy.ByteString -> Data.Text.Lazy.Text +bytesToTextUtf8UnsafeLazy = Data.Text.Lazy.Encoding.decodeUtf8 + +-- | decode a Text from a ByteString that is assumed to be UTF-8, +-- replace non-UTF-8 characters with the replacment char U+FFFD. +bytesToTextUtf8Lenient :: Data.ByteString.ByteString -> Data.Text.Text +bytesToTextUtf8Lenient = + Data.Text.Encoding.decodeUtf8With Data.Text.Encoding.Error.lenientDecode + +-- | decode a lazy Text from a lazy ByteString that is assumed to be UTF-8, +-- replace non-UTF-8 characters with the replacment char U+FFFD. +bytesToTextUtf8LenientLazy :: Data.ByteString.Lazy.ByteString -> Data.Text.Lazy.Text +bytesToTextUtf8LenientLazy = + Data.Text.Lazy.Encoding.decodeUtf8With Data.Text.Encoding.Error.lenientDecode + +-- | Make a lazy 'Text' strict. +toStrict :: Data.Text.Lazy.Text -> Text +toStrict = Data.Text.Lazy.toStrict + +-- | Make a strict 'Text' lazy. +toLazy :: Text -> Data.Text.Lazy.Text +toLazy = Data.Text.Lazy.fromStrict + +-- | Make a lazy 'ByteString' strict. +toStrictBytes :: Data.ByteString.Lazy.ByteString -> ByteString +toStrictBytes = Data.ByteString.Lazy.toStrict + +-- | Make a strict 'ByteString' lazy. +toLazyBytes :: ByteString -> Data.ByteString.Lazy.ByteString +toLazyBytes = Data.ByteString.Lazy.fromStrict + +-- | Convert a (performant) 'Text' into an (imperformant) list-of-char 'String'. +-- +-- Some libraries (like @time@ or @network-uri@) still use the `String` as their interface. We only want to convert to string at the edges, otherwise use 'Text'. +-- +-- ATTN: Don’t use `String` in code if you can avoid it, prefer `Text` instead. +textToString :: Text -> String +textToString = Data.Text.unpack + +-- | Convert an (imperformant) list-of-char 'String' into a (performant) 'Text' . +-- +-- Some libraries (like @time@ or @network-uri@) still use the `String` as their interface. We want to convert 'String' to 'Text' as soon as possible and only use 'Text' in our code. +-- +-- ATTN: Don’t use `String` in code if you can avoid it, prefer `Text` instead. +stringToText :: String -> Text +stringToText = Data.Text.pack + +-- | Encode a String to an UTF-8 encoded Bytestring +-- +-- ATTN: Don’t use `String` in code if you can avoid it, prefer `Text` instead. +stringToBytesUtf8 :: String -> ByteString +-- TODO(Profpatsch): use a stable interface +stringToBytesUtf8 = GHC.utf8EncodeByteString + +-- | Like `show`, but generate a 'Text' +-- +-- ATTN: This goes via `String` and thus is fairly inefficient. +-- We should add a good display library at one point. +-- +-- ATTN: unlike `show`, this forces the whole @'a +-- so only use if you want to display the whole thing. +showToText :: (Show a) => a -> Text +showToText = stringToText . show + +-- | Unsafe conversion between 'Char' and 'Word8'. This is a no-op and +-- silently truncates to 8 bits Chars > '\255'. It is provided as +-- convenience for ByteString construction. +-- +-- Use if you want to get the 'Word8' representation of a character literal. +-- Don’t use on arbitrary characters! +-- +-- >>> charToWordUnsafe ',' +-- 44 +charToWordUnsafe :: Char -> Word8 +{-# INLINE charToWordUnsafe #-} +charToWordUnsafe = fromIntegral . Data.Char.ord + +pattern IsEmpty :: [a] +pattern IsEmpty <- (null -> True) + where + IsEmpty = [] + +pattern IsNonEmpty :: NonEmpty a -> [a] +pattern IsNonEmpty n <- (nonEmpty -> Just n) + where + IsNonEmpty n = toList n + +{-# COMPLETE IsEmpty, IsNonEmpty #-} + +-- | Single element in a (non-empty) list. +singleton :: a -> NonEmpty a +singleton a = a :| [] + +-- | If the given list is empty, use the given default element and return a non-empty list. +nonEmptyDef :: a -> [a] -> NonEmpty a +nonEmptyDef def xs = + xs & nonEmpty & \case + Nothing -> def :| [] + Just ne -> ne + +-- | If the list is not empty, run the given function with a NonEmpty list, otherwise just return [] +overNonEmpty :: (Applicative f) => (NonEmpty a -> f [b]) -> [a] -> f [b] +overNonEmpty f xs = case xs of + IsEmpty -> pure [] + IsNonEmpty xs' -> f xs' + +-- | Zip two non-empty lists. +zipNonEmpty :: NonEmpty a -> NonEmpty b -> NonEmpty (a, b) +{-# INLINE zipNonEmpty #-} +zipNonEmpty ~(a :| as) ~(b :| bs) = (a, b) :| zip as bs + +-- | Zip two non-empty lists, combining them with the given function +zipWithNonEmpty :: (a -> b -> c) -> NonEmpty a -> NonEmpty b -> NonEmpty c +{-# INLINE zipWithNonEmpty #-} +zipWithNonEmpty = NonEmpty.zipWith + +-- | Zip three non-empty lists. +zip3NonEmpty :: NonEmpty a -> NonEmpty b -> NonEmpty c -> NonEmpty (a, b, c) +{-# INLINE zip3NonEmpty #-} +zip3NonEmpty ~(a :| as) ~(b :| bs) ~(c :| cs) = (a, b, c) :| zip3 as bs cs + +-- | Zip three non-empty lists, combining them with the given function +zipWith3NonEmpty :: (a -> b -> c -> d) -> NonEmpty a -> NonEmpty b -> NonEmpty c -> NonEmpty d +{-# INLINE zipWith3NonEmpty #-} +zipWith3NonEmpty f ~(x :| xs) ~(y :| ys) ~(z :| zs) = f x y z :| zipWith3 f xs ys zs + +-- | Zip four non-empty lists +zip4NonEmpty :: NonEmpty a -> NonEmpty b -> NonEmpty c -> NonEmpty d -> NonEmpty (a, b, c, d) +{-# INLINE zip4NonEmpty #-} +zip4NonEmpty ~(a :| as) ~(b :| bs) ~(c :| cs) ~(d :| ds) = (a, b, c, d) :| zip4 as bs cs ds + +-- | We don’t want to use Foldable’s `length`, because it is too polymorphic and can lead to bugs. +-- Only list-y things should have a length. +class (Foldable f) => Lengthy f + +instance Lengthy [] + +instance Lengthy NonEmpty + +instance Lengthy Vector + +lengthNatural :: (Lengthy f) => f a -> Natural +lengthNatural xs = + xs + & Foldable.length + -- length can never be negative or something went really, really wrong + & fromIntegral @Int @Natural + +-- | @O(n)@. Get the maximum element from a non-empty structure (strict). +maximum1 :: (Foldable1 f, Ord a) => f a -> a +maximum1 = Foldl1.fold1 Foldl1.maximum + +-- | @O(n)@. Get the maximum element from a non-empty structure, using the given comparator (strict). +maximumBy1 :: (Foldable1 f) => (a -> a -> Ordering) -> f a -> a +maximumBy1 f = Foldl1.fold1 (Foldl1.maximumBy f) + +-- | @O(n)@. Get the minimum element from a non-empty structure (strict). +minimum1 :: (Foldable1 f, Ord a) => f a -> a +minimum1 = Foldl1.fold1 Foldl1.minimum + +-- | @O(n)@. Get the minimum element from a non-empty structure, using the given comparator (strict). +minimumBy1 :: (Foldable1 f) => (a -> a -> Ordering) -> f a -> a +minimumBy1 f = Foldl1.fold1 (Foldl1.minimumBy f) + +-- | Annotate a 'Maybe' with an error message and turn it into an 'Either'. +annotate :: err -> Maybe a -> Either err a +annotate err = \case + Nothing -> Left err + Just a -> Right a + +-- | Map the same function over both sides of a Bifunctor (e.g. a tuple). +both :: (Bifunctor bi) => (a -> b) -> bi a a -> bi b b +both f = bimap f f + +-- | Find the first element for which pred returns `Just a`, and return the `a`. +-- +-- Example: +-- @ +-- >>> :set -XTypeApplications +-- >>> import qualified Text.Read +-- +-- >>> findMaybe (Text.Read.readMaybe @Int) ["foo"] +-- Nothing +-- >>> findMaybe (Text.Read.readMaybe @Int) ["foo", "34.40", "34", "abc"] +-- Just 34 +findMaybe :: (Foldable t) => (a -> Maybe b) -> t a -> Maybe b +findMaybe mPred list = + let pred' x = Maybe.isJust $ mPred x + in case Foldable.find pred' list of + Just a -> mPred a + Nothing -> Nothing + +-- | 'traverse' with a function returning 'Either' and collect all errors that happen, if they happen. +-- +-- Does not shortcut on error, so will always traverse the whole list/'Traversable' structure. +-- +-- This is a useful error handling function in many circumstances, +-- because it won’t only return the first error that happens, but rather all of them. +traverseValidate :: forall t a err b. (Traversable t) => (a -> Either err b) -> t a -> Either (NonEmpty err) (t b) +traverseValidate f as = + as + & traverse @t @(Validation _) (eitherToListValidation . f) + & validationToEither + +-- | 'traverse' with a function returning 'm Either' and collect all errors that happen, if they happen. +-- +-- Does not shortcut on error, so will always traverse the whole list/'Traversable' structure. +-- +-- This is a useful error handling function in many circumstances, +-- because it won’t only return the first error that happens, but rather all of them. +traverseValidateM :: forall t m a err b. (Traversable t, Applicative m) => (a -> m (Either err b)) -> t a -> m (Either (NonEmpty err) (t b)) +traverseValidateM f as = + as + & traverse @t @m (\a -> a & f <&> eitherToListValidation) + <&> sequenceA @t @(Validation _) + <&> validationToEither + +-- | 'traverse_' with a function returning 'm Either' and collect all errors that happen, if they happen. +-- +-- Does not shortcut on error, so will always traverse the whole list/'Traversable' structure. +-- +-- This is a useful error handling function in many circumstances, +-- because it won’t only return the first error that happens, but rather all of them. +traverseValidateM_ :: forall t m a err. (Traversable t, Applicative m) => (a -> m (Either err ())) -> t a -> m (Either (NonEmpty err) ()) +traverseValidateM_ f as = + as + & traverse @t @m (\a -> a & f <&> eitherToListValidation) + <&> sequenceA_ @t @(Validation _) + <&> validationToEither + +-- | Like 'eitherToValidation', but puts the Error side into a NonEmpty list +-- to make it combine with other validations. +-- +-- See also 'validateEithers', if you have a list of Either and want to collect all errors. +eitherToListValidation :: Either a c -> Validation (NonEmpty a) c +eitherToListValidation = first singleton . eitherToValidation + +-- | Convert an 'Either' to a 'These'. +eitherToThese :: Either err a -> These err a +eitherToThese (Left err) = This err +eitherToThese (Right a) = That a + +-- | Like 'eitherToThese', but puts the Error side into a NonEmpty list +-- to make it combine with other theses. +eitherToListThese :: Either err a -> These (NonEmpty err) a +eitherToListThese (Left e) = This (singleton e) +eitherToListThese (Right a) = That a + +-- | Convert a 'Validation' to a 'These'. +validationToThese :: Validation err a -> These err a +validationToThese (Failure err) = This err +validationToThese (Success a) = That a + +-- | Nested '>>=' of a These inside some other @m@. +-- +-- Use if you want to collect errors and successes, and want to chain multiple function returning 'These'. +thenThese :: + (Monad m, Semigroup err) => + (a -> m (These err b)) -> + m (These err a) -> + m (These err b) +thenThese f x = do + th <- x + join <$> traverse f th + +-- | Nested validating bind-like combinator. +-- +-- Use if you want to collect errors, and want to chain multiple functions returning 'Validation'. +thenValidate :: + (a -> Validation err b) -> + Validation err a -> + Validation err b +thenValidate f = \case + Success a -> f a + Failure err -> Failure err + +-- | Nested validating bind-like combinator inside some other @m@. +-- +-- Use if you want to collect errors, and want to chain multiple functions returning 'Validation'. +thenValidateM :: + (Monad m) => + (a -> m (Validation err b)) -> + m (Validation err a) -> + m (Validation err b) +thenValidateM f x = + eitherToValidation <$> do + x' <- validationToEither <$> x + case x' of + Left err -> pure $ Left err + Right a -> validationToEither <$> f a + +-- | Put the text to @stderr@. +putStderrLn :: Text -> IO () +putStderrLn msg = + System.IO.hPutStrLn System.IO.stderr $ textToString msg + +exitWithMessage :: Text -> IO a +exitWithMessage msg = do + putStderrLn msg + System.Exit.exitWith $ System.Exit.ExitFailure (-1) + +-- | Run some function producing applicative over a traversable data structure, +-- then collect the results in a Monoid. +-- +-- Very helpful with side-effecting functions returning @(Validation err a)@: +-- +-- @ +-- let +-- f :: Text -> IO (Validation (NonEmpty Error) Text) +-- f t = pure $ if t == "foo" then Success t else Failure (singleton ("not foo: " <> t)) +-- +-- in traverseFold f [ "foo", "bar", "baz" ] +-- == Failure ("not foo bar" :| ["not foo baz"]) +-- @ +-- +-- … since @(Semigroup err => Validation err a)@ is a @Semigroup@/@Monoid@ itself. +traverseFold :: (Applicative ap, Traversable t, Monoid m) => (a -> ap m) -> t a -> ap m +{-# INLINE traverseFold #-} +traverseFold f xs = + -- note: could be weakened to (Foldable t) via `getAp . foldMap (Ap . f)` + fold <$> traverse f xs + +-- | Like 'traverseFold', but fold over a semigroup instead of a Monoid, by providing a starting element. +traverseFoldDefault :: (Applicative ap, Traversable t, Semigroup m) => m -> (a -> ap m) -> t a -> ap m +{-# INLINE traverseFoldDefault #-} +traverseFoldDefault def f xs = foldDef def <$> traverse f xs + where + foldDef = foldr (<>) + +-- | Same as 'traverseFold', but with a 'Semigroup' and 'Traversable1' restriction. +traverseFold1 :: (Applicative ap, Traversable1 t, Semigroup s) => (a -> ap s) -> t a -> ap s +{-# INLINE traverseFold1 #-} +-- note: cannot be weakened to (Foldable1 t) because there is no `Ap` for Semigroup (No `Apply` typeclass) +traverseFold1 f xs = fold1 <$> traverse f xs + +-- | Use this in places where the code is still to be implemented. +-- +-- It always type-checks and will show a warning at compile time if it was forgotten in the code. +-- +-- Use instead of 'error' and 'undefined' for code that hasn’t been written. +-- +-- Uses the same trick as https://hackage.haskell.org/package/protolude-0.3.0/docs/src/Protolude.Error.html#error +{-# WARNING todo "'todo' (undefined code) remains in code" #-} +todo :: forall (r :: RuntimeRep). forall (a :: TYPE r). (HasCallStack) => a +todo = raise# (errorCallWithCallStackException "This code was not yet implemented: TODO" ?callStack) + +-- | Convert an integer to a 'Natural' if possible +-- +-- Named the same as the function from "GHC.Natural", but does not crash. +intToNatural :: (Integral a) => a -> Maybe Natural +intToNatural i = + if i < 0 + then Nothing + else Just $ fromIntegral i + +-- | @inverseFunction f@ creates a function that is the inverse of a given function +-- @f@. It does so by constructing 'M.Map' internally for each value @f a@. The +-- implementation makes sure that the 'M.Map' is constructed only once and then +-- shared for every call. +-- +-- __Memory usage note:__ don't inverse functions that have types like 'Int' +-- as their result. In this case the created 'M.Map' will have huge size. +-- +-- The complexity of reversed mapping is \(\mathcal{O}(\log n)\). +-- +-- __Performance note:__ make sure to specialize monomorphic type of your functions +-- that use 'inverseFunction' to avoid 'M.Map' reconstruction. +-- +-- One of the common 'inverseFunction' use-case is inverting the 'show' or a 'show'-like +-- function. +-- +-- >>> data Color = Red | Green | Blue deriving (Show, Enum, Bounded) +-- >>> parse = inverseFunction show :: String -> Maybe Color +-- >>> parse "Red" +-- Just Red +-- >>> parse "Black" +-- Nothing +-- +-- __Correctness note:__ 'inverseFunction' expects /injective function/ as its argument, +-- i.e. the function must map distinct arguments to distinct values. +-- +-- Typical usage of this function looks like this: +-- +-- @ +-- __data__ GhcVer +-- = Ghc802 +-- | Ghc822 +-- | Ghc844 +-- | Ghc865 +-- | Ghc881 +-- __deriving__ ('Eq', 'Ord', 'Show', 'Enum', 'Bounded') +-- +-- showGhcVer :: GhcVer -> 'Text' +-- showGhcVer = \\__case__ +-- Ghc802 -> "8.0.2" +-- Ghc822 -> "8.2.2" +-- Ghc844 -> "8.4.4" +-- Ghc865 -> "8.6.5" +-- Ghc881 -> "8.8.1" +-- +-- parseGhcVer :: 'Text' -> 'Maybe' GhcVer +-- parseGhcVer = 'inverseFunction' showGhcVer +-- +-- Taken from relude’s @Relude.Extra.Enum@. +inverseFunction :: + forall a k. + (Bounded a, Enum a, Ord k) => + (a -> k) -> + (k -> Maybe a) +inverseFunction f k = Map.lookup k $ inverseMap f + +-- | Like `inverseFunction`, but instead of returning the function +-- it returns a mapping from all possible outputs to their possible inputs. +-- +-- This has the same restrictions of 'inverseFunction'. +inverseMap :: forall a k. (Bounded a, Enum a, Ord k) => (a -> k) -> Map k a +inverseMap f = enumerateAll <&> (\a -> (f a, a)) & Map.fromList + +-- | All possible values in this enum. +enumerateAll :: (Enum a, Bounded a) => [a] +enumerateAll = [minBound .. maxBound] + +-- | Create a 'Map' from a list of values, extracting the map key from each value. Like 'Map.fromList'. +-- +-- Attention: if the key is not unique, the earliest value with the key will be in the map. +mapFromListOn :: (Ord key) => (a -> key) -> [a] -> Map key a +mapFromListOn f xs = xs <&> (\x -> (f x, x)) & Map.fromList + +-- | Create a 'Map' from a list of values, merging multiple values at the same key with '<>' (left-to-right) +-- +-- `f` has to extract the key and value. Value must be mergable. +-- +-- Attention: if the key is not unique, the earliest value with the key will be in the map. +mapFromListOnMerge :: (Ord key, Semigroup s) => (a -> (key, s)) -> [a] -> Map key s +mapFromListOnMerge f xs = + xs + <&> (\x -> f x) + & Map.fromListWith + -- we have to flip (`<>`) because `Map.fromListWith` merges its values “the other way around” + (flip (<>)) + +-- | If the predicate is true, return the @m@, else 'mempty'. +-- +-- This can be used (together with `ifExists`) to e.g. create lists with optional elements: +-- +-- >>> import Data.Monoid (Sum(..)) +-- +-- >>> :{ mconcat [ +-- ifTrue (1 == 1) [1], +-- [2, 3, 4], +-- ifTrue False [5], +-- ] +-- :} +-- [1,2,3,4] +-- +-- Or any other Monoid: +-- +-- >>> mconcat [ Sum 1, ifTrue (1 == 1) (Sum 2), Sum 3 ] + +-- Sum {getSum = 6} + +ifTrue :: (Monoid m) => Bool -> m -> m +ifTrue pred' m = if pred' then m else mempty + +-- | If the given @Maybe@ is @Just@, return the result of `f` wrapped in `pure`, else return `mempty`. + +-- This can be used (together with `ifTrue`) to e.g. create lists with optional elements: +-- +-- >>> import Data.Monoid (Sum(..)) +-- +-- >>> :{ mconcat [ +-- unknown command '{' +-- +-- Or any other Monoid: +-- +-- >>> mconcat [ Sum 1, ifExists id (Just 2), Sum 3 ] +-- Sum {getSum = 6} + +ifExists :: (Monoid (f b), Applicative f) => (a -> b) -> Maybe a -> f b +ifExists f m = m & foldMap @Maybe (pure . f) |