    -- | The Witch package is a library that allows you to confidently convert
    -- values between various types. This module exports everything you need to
    -- perform conversions or define your own. It is designed to be imported
    -- unqualified, so getting started is as easy as:
    --
    -- >>> import Witch
    --
    -- In typical usage, the functions that you will use most often are
    -- 'Witch.Utility.into' for conversions that always succeed and
    -- 'Witch.Utility.tryInto' for conversions that sometimes fail.
    --
    -- Please consider reading the blog post that announces this library:
    -- <https://taylor.fausak.me/2021/07/13/witch/>
    module Witch
      ( -- * Type classes

        -- ** From
        Witch.From.From (from),
        Witch.Utility.into,

        -- ** TryFrom
        Witch.TryFrom.TryFrom (tryFrom),
        Witch.Utility.tryInto,

        -- * Data types
        Witch.TryFromException.TryFromException (..),

        -- ** Encodings
        Witch.Encoding.ISO_8859_1,
        Witch.Encoding.UTF_8,
        Witch.Encoding.UTF_16LE,
        Witch.Encoding.UTF_16BE,
        Witch.Encoding.UTF_32LE,
        Witch.Encoding.UTF_32BE,

        -- * Utilities
        Witch.Utility.via,
        Witch.Utility.tryVia,
        Witch.Utility.maybeTryFrom,
        Witch.Utility.eitherTryFrom,

        -- ** Unsafe

        -- | These functions should only be used in two circumstances: When you know
        -- a conversion is safe even though you can't prove it to the compiler, and
        -- when you're alright with your program crashing if the conversion fails.
        -- In all other cases you should prefer the normal conversion functions like
        -- 'Witch.TryFrom.tryFrom'. And if you're converting a literal value,
        -- consider using the Template Haskell conversion functions like
        -- 'Witch.Lift.liftedFrom'.
        Witch.Utility.unsafeFrom,
        Witch.Utility.unsafeInto,

        -- ** Template Haskell

        -- | This library uses /typed/ Template Haskell, which may be a little
        -- different than what you're used to. Normally Template Haskell uses the
        -- @$(...)@ syntax for splicing in things to run at compile time. The typed
        -- variant uses the @$$(...)@ syntax for splices, doubling up on the dollar
        -- signs. Other than that, using typed Template Haskell should be pretty
        -- much the same as using regular Template Haskell.
        Witch.Lift.liftedFrom,
        Witch.Lift.liftedInto,

        -- * Notes

        -- ** Motivation

        -- | Haskell provides many ways to convert between common types, and core
        -- libraries add even more. It can be challenging to know which function to
        -- use when converting from some source type @a@ to some target type @b@. It
        -- can be even harder to know if that conversion is safe or if there are any
        -- pitfalls to watch out for.
        --
        -- This library tries to address that problem by providing a common
        -- interface for converting between types. The 'Witch.From.From' type class
        -- is for conversions that cannot fail, and the 'Witch.TryFrom.TryFrom' type
        -- class is for conversions that can fail. These type classes are inspired
        -- by the [@From@](https://doc.rust-lang.org/std/convert/trait.From.html)
        -- trait in Rust.

        -- ** Type applications

        -- | Although you can use this library without the [@TypeApplications@](https://downloads.haskell.org/ghc/9.6.1/docs/users_guide/exts/type_applications.html)
        -- language extension, the extension is strongly recommended. Since most
        -- functions provided by this library are polymorphic in at least one type
        -- variable, it's easy to use them in a situation that would be ambiguous.
        -- Normally you could resolve the ambiguity with an explicit type signature,
        -- but type applications are much more ergonomic. For example:
        --
        -- > -- Avoid this:
        -- > f . (from :: Int8 -> Int16) . g
        -- >
        -- > -- Prefer this:
        -- > f . from @Int8 @Int16 . g
        --
        -- Most functions in this library have two versions with their type
        -- variables in opposite orders. That's because usually one side of the
        -- conversion or the other already has its type inferred by context. In
        -- those situations it makes sense to only provide one type argument.
        --
        -- > -- Avoid this: (assuming f :: Int16 -> ...)
        -- > f $ from @Int8 @Int16 0
        -- >
        -- > -- Prefer this:
        -- > f $ from @Int8 0
        --
        -- > -- Avoid this: (assuming x :: Int8)
        -- > g $ from @Int8 @Int16 x
        -- >
        -- > -- Prefer this:
        -- > g $ into @Int16 x

        -- ** Alternatives

        -- | Many Haskell libraries already provide similar functionality. How is
        -- this library different?
        --
        -- - [@Coercible@](https://hackage.haskell.org/package/base-4.15.0.0/docs/Data-Coerce.html#t:Coercible):
        --   This type class is solved by the compiler, but it only works for types
        --   that have the same runtime representation. This is very convenient for
        --   @newtype@s, but it does not work for converting between arbitrary types
        --   like @Int8@ and @Int16@.
        --
        -- - [@Convertible@](https://hackage.haskell.org/package/convertible-1.1.1.0/docs/Data-Convertible-Base.html#t:Convertible):
        --   This popular conversion type class is similar to what this library
        --   provides. The main difference is that it does not differentiate between
        --   conversions that can fail and those that cannot.
        --
        -- - [@From@](https://hackage.haskell.org/package/basement-0.0.11/docs/Basement-From.html#t:From):
        --   This type class is almost identical to what this library provides.
        --   Unfortunately it is part of the @basement@ package, which is an
        --   alternative standard library that some people may not want to depend
        --   on.
        --
        -- - [@Inj@](https://hackage.haskell.org/package/inj-1.0/docs/Inj.html#t:Inj):
        --   This type class requires instances to be an injection, which means that
        --   no two input values should map to the same output. That restriction
        --   prohibits many useful instances. Also many instances throw impure
        --   exceptions.
        --
        -- In addition to those general-purpose type classes, there are many
        -- alternatives for more specific conversions. How does this library compare
        -- to those?
        --
        -- - Monomorphic conversion functions like [@Data.Text.pack@](https://hackage.haskell.org/package/text-1.2.4.1/docs/Data-Text.html#v:pack)
        --   are explicit but not necessarily convenient. It can be tedious to
        --   manage the imports necessary to use the functions. And if you want to
        --   put them in a custom prelude, you will have to come up with your own
        --   names.
        --
        -- - Polymorphic conversion methods like 'toEnum' are more convenient but
        --   may have unwanted semantics or runtime behavior. For example the 'Enum'
        --   type class is more or less tied to the 'Int' data type and frequently
        --   throws impure exceptions.
        --
        -- - Polymorphic conversion functions like 'fromIntegral' are very
        --   convenient. Unfortunately it can be challenging to know which types
        --   have the instances necessary to make the conversion possible. And even
        --   if the conversion is possible, is it safe? For example converting a
        --   negative 'Int' into a 'Word' will overflow, which may be surprising.

        -- ** Instances

        -- | When should you add a 'Witch.From.From' (or 'Witch.TryFrom.TryFrom')
        -- instance for some pair of types? This is a surprisingly tricky question
        -- to answer precisely. Instances are driven more by guidelines than rules.
        --
        -- - Conversions must not throw impure exceptions. This means no 'undefined'
        --   or anything equivalent to it.
        --
        -- - Conversions should be unambiguous. If there are multiple reasonable
        --   ways to convert from @a@ to @b@, then you probably should not add a
        --   'Witch.From.From' instance for them.
        --
        -- - Conversions should be lossless. If you have @From a b@ then no two @a@
        --   values should be converted to the same @b@ value.
        --
        --     - Some conversions necessarily lose information, like converting from
        --       a list into a set.
        --
        -- - If you have both @From a b@ and @From b a@, then
        --   @from \@b \@a . from \@a \@b@ should be the same as 'id'. In other
        --   words, @a@ and @b@ are isomorphic.
        --
        --     - This often true, but not always. For example, converting a list
        --       into a set will remove duplicates. And then converting back into a
        --       list will put the elements in ascending order.
        --
        -- - If you have both @From a b@ and @From b c@, then you could also have
        --   @From a c@ and it should be the same as @from \@b \@c . from \@a \@b@.
        --   In other words, @From@ is transitive.
        --
        --     - This is not always true. For example an @Int8@ may be represented
        --       as a number in JSON, whereas an @Int64@ might be represented as a
        --       string. That means @into \@JSON (into \@Int64 int8)@ would not be
        --       the same as @into \@JSON int8@.
        --
        -- - You should not have both a @From@ instance and a @TryFrom@ instance for
        --   the same pair of types.
        --
        -- - If you have a @From@ or @TryFrom@ instance for a pair of types, then
        --   you should probably have a @From@ or @TryFrom@ instance for the same
        --   pair of types but in the opposite direction. In other words if you have
        --   @From a b@ then you should have @From b a@ or @TryFrom b a@.
        --
        -- In general if @s@ /is/ a @t@, then you should add a 'Witch.From.From'
        -- instance for it. But if @s@ merely /can be/ a @t@, then you could add a
        -- 'Witch.TryFrom.TryFrom' instance for it. And if it is technically
        -- possible to convert from @s@ to @t@ but there are a lot of caveats, you
        -- probably should not write any instances at all.

        -- ** Laws

        -- | As the previous section notes, there aren't any cut and dried laws for
        -- the @From@ and @TryFrom@ type classes. However it can be useful to
        -- consider the following equations for guiding instances:
        --
        -- > -- same strictness
        -- > seq (from @a @b x) y = seq x y
        -- > seq (tryFrom @a @b x) y = seq x y
        --
        -- > -- round trip
        -- > from @b @a (from @a @b x) = x
        --
        -- > -- transitive
        -- > from @b @c (from @a @b x) = from @a @c x
        -- > tryFrom @b @a (from @a @b x) = Right x
        -- > if isRight (tryFrom @a @b x) then
        -- >   fmap (from @b @a) (tryFrom @a @b x) = Right x
        -- > if isRight (tryFrom @a @b x) then do
        -- >   fmap (tryFrom @b @a) (tryFrom @a @b x) = Right (Right x)

        -- ** Integral types

        -- | There are a lot of types that represent various different ranges of
        -- integers, and Witch may not provide the instances you want. In particular
        -- it does not provide a total way to convert from an @Int32@ into an @Int@.
        -- Why is that?
        --
        -- The Haskell Language Report only demands that @Int@s have at least 30
        -- bits of precision. That means a reasonable Haskell implementation could
        -- have an @Int@ type that's smaller than the @Int32@ type.
        --
        -- However in practice everyone uses the same Haskell implementation: GHC.
        -- And with GHC the @Int@ type always has 32 bits of precision, even on
        -- 32-bit architectures. So for almost everybody, it's probably safe to use
        -- @unsafeFrom \@Int32 \@Int@. Similarly most software these days runs on
        -- machines with 64-bit architectures. That means it's also probably safe
        -- for you to use @unsafeFrom \@Int64 \@Int@.
        --
        -- All of the above also applies for @Word@, @Word32@, and @Word64@.

        -- ** Downsides

        -- | As the author of this library, I obviously think that everyone should
        -- use it because it's the greatest thing since sliced bread. But nothing is
        -- perfect, so what are some downsides to this library?
        --
        -- - More specific type classes are often better. For example, @IsString s@
        --   is more useful that @From String s@. The former says that the type @s@
        --   is the same as a string literal, but the latter just says you can
        --   produce a value of type @s@ when given a string.
        --
        -- - The @From@ type class works great for specific pairs of types, but can
        --   get confusing when it's polymorphic. For example if you have some
        --   function with a @From s t@ constraint, that doesn't really tell you
        --   anything about what it's doing.
      )
    where

    import qualified Witch.Encoding
    import qualified Witch.From
    import Witch.Instances ()
    import qualified Witch.Lift
    import qualified Witch.TryFrom
    import qualified Witch.TryFromException
    import qualified Witch.Utility