{-# LANGUAGE MagicHash, NoImplicitPrelude, TypeFamilies, UnboxedTuples #-}
-----------------------------------------------------------------------------
-- |
-- Module      :  GHC.Types
-- Copyright   :  (c) The University of Glasgow 2009
-- License     :  see libraries/ghc-prim/LICENSE
--
-- Maintainer  :  cvs-ghc@haskell.org
-- Stability   :  internal
-- Portability :  non-portable (GHC Extensions)
--
-- GHC type definitions.
-- Use GHC.Exts from the base package instead of importing this
-- module directly.
--
-----------------------------------------------------------------------------

module GHC.Types (
        Bool(..), Char(..), Int(..), Word(..),
        Float(..), Double(..),
        Ordering(..), IO(..),
        isTrue#,
        SPEC(..)
    ) where

import GHC.Prim


infixr 5 :

data [] a = [] | a : [a]

data {-# CTYPE "HsBool" #-} Bool = False | True

{- | The character type 'Char' is an enumeration whose values represent
Unicode (or equivalently ISO\/IEC 10646) characters (see
<http://www.unicode.org/> for details).  This set extends the ISO 8859-1
(Latin-1) character set (the first 256 characters), which is itself an extension
of the ASCII character set (the first 128 characters).  A character literal in
Haskell has type 'Char'.

To convert a 'Char' to or from the corresponding 'Int' value defined
by Unicode, use 'Prelude.toEnum' and 'Prelude.fromEnum' from the
'Prelude.Enum' class respectively (or equivalently 'ord' and 'chr').
-}
data {-# CTYPE "HsChar" #-} Char = C# Char#

-- | A fixed-precision integer type with at least the range @[-2^29 .. 2^29-1]@.
-- The exact range for a given implementation can be determined by using
-- 'Prelude.minBound' and 'Prelude.maxBound' from the 'Prelude.Bounded' class.
data {-# CTYPE "HsInt" #-} Int = I# Int#

-- |A 'Word' is an unsigned integral type, with the same size as 'Int'.
data {-# CTYPE "HsWord" #-} Word = W# Word#

-- | Single-precision floating point numbers.
-- It is desirable that this type be at least equal in range and precision
-- to the IEEE single-precision type.
data {-# CTYPE "HsFloat" #-} Float = F# Float#

-- | Double-precision floating point numbers.
-- It is desirable that this type be at least equal in range and precision
-- to the IEEE double-precision type.
data {-# CTYPE "HsDouble" #-} Double = D# Double#

data Ordering = LT | EQ | GT

{- |
A value of type @'IO' a@ is a computation which, when performed,
does some I\/O before returning a value of type @a@.

There is really only one way to \"perform\" an I\/O action: bind it to
@Main.main@ in your program.  When your program is run, the I\/O will
be performed.  It isn't possible to perform I\/O from an arbitrary
function, unless that function is itself in the 'IO' monad and called
at some point, directly or indirectly, from @Main.main@.

'IO' is a monad, so 'IO' actions can be combined using either the do-notation
or the '>>' and '>>=' operations from the 'Monad' class.
-}
newtype IO a = IO (State# RealWorld -> (# State# RealWorld, a #))


-- | A data constructor used to box up all unlifted equalities
--
-- The type constructor is special in that GHC pretends that it
-- has kind (? -> ? -> Fact) rather than (* -> * -> *)
data (~) a b = Eq# ((~#) a b)


-- Despite this not being exported here, the documentation will
-- be used by haddock, hence the user-facing blurb here, and not in primops.txt.pp:

-- | This two-parameter class has instances for types @a@ and @b@ if
--      the compiler can infer that they have the same representation. This class
--      does not have regular instances; instead they are created on-the-fly during
--      type-checking. Trying to manually declare an instance of @Coercible@
--      is an error.
--
--      Nevertheless one can pretend that the following three kinds of instances
--      exist. First, as a trivial base-case:
--
--      @instance a a@
--
--      Furthermore, for every type constructor there is
--      an instance that allows to coerce under the type constructor. For
--      example, let @D@ be a prototypical type constructor (@data@ or
--      @newtype@) with three type arguments, which have roles @nominal@,
--      @representational@ resp. @phantom@. Then there is an instance of
--      the form
--
--      @instance Coercible b b\' => Coercible (D a b c) (D a b\' c\')@
--
--      Note that the @nominal@ type arguments are equal, the
--      @representational@ type arguments can differ, but need to have a
--      @Coercible@ instance themself, and the @phantom@ type arguments can be
--      changed arbitrarily.
--
--      The third kind of instance exists for every @newtype NT = MkNT T@ and
--      comes in two variants, namely
--
--      @instance Coercible a T => Coercible a NT@
--
--      @instance Coercible T b => Coercible NT b@
--
--      This instance is only usable if the constructor @MkNT@ is in scope.
--
--      If, as a library author of a type constructor like @Set a@, you
--      want to prevent a user of your module to write
--      @coerce :: Set T -> Set NT@,
--      you need to set the role of @Set@\'s type parameter to @nominal@,
--      by writing
--
--      @type role Set nominal@
--
--      For more details about this feature, please refer to
--      <http://www.cis.upenn.edu/~eir/papers/2014/coercible/coercible.pdf Safe Coercions>
--      by Joachim Breitner, Richard A. Eisenberg, Simon Peyton Jones and Stephanie Weirich.
--
--      /Since: 4.7.0.0/
data Coercible a b = MkCoercible ((~#) a b)

-- | Alias for tagToEnum#. Returns True of its parameter is 1# and False
--   if it is 0#.

{-# INLINE isTrue# #-}
isTrue# :: Int# -> Bool   -- See Note [Optimizing isTrue#]
isTrue# x = tagToEnum# x

-- Note [Optimizing isTrue#]
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--
-- Current definition of isTrue# is a temporary workaround. We would like to
-- have functions isTrue# and isFalse# defined like this:
--
--     isTrue# :: Int# -> Bool
--     isTrue# 1# = True
--     isTrue# _  = False
--
--     isFalse# :: Int# -> Bool
--     isFalse# 0# = True
--     isFalse# _  = False
--
-- These functions would allow us to safely check if a tag can represent True
-- or False. Using isTrue# and isFalse# as defined above will not introduce
-- additional case into the code. When we scrutinize return value of isTrue#
-- or isFalse#, either explicitly in a case expression or implicitly in a guard,
-- the result will always be a single case expression (given that optimizations
-- are turned on). This results from case-of-case transformation. Consider this
-- code (this is both valid Haskell and Core):
--
-- case isTrue# (a ># b) of
--     True  -> e1
--     False -> e2
--
-- Inlining isTrue# gives:
--
-- case (case (a ># b) of { 1# -> True; _ -> False } ) of
--     True  -> e1
--     False -> e2
--
-- Case-of-case transforms that to:
--
-- case (a ># b) of
--   1# -> case True of
--           True  -> e1
--           False -> e2
--   _  -> case False of
--           True  -> e1
--           False -> e2
--
-- Which is then simplified by case-of-known-constructor:
--
-- case (a ># b) of
--   1# -> e1
--   _  -> e2
--
-- While we get good Core here, the code generator will generate very bad Cmm
-- if e1 or e2 do allocation. It will push heap checks into case alternatives
-- which results in about 2.5% increase in code size. Until this is improved we
-- just make isTrue# an alias to tagToEnum#. This is a temporary solution (if
-- you're reading this in 2023 then things went wrong). See #8326.
--

-- | SPEC is used by GHC in the @SpecConstr@ pass in order to inform
-- the compiler when to be particularly aggressive. In particular, it
-- tells GHC to specialize regardless of size or the number of
-- specializations. However, not all loops fall into this category.
--
-- Libraries can specify this by using 'SPEC' data type to inform which
-- loops should be aggressively specialized.
data SPEC = SPEC | SPEC2
