ghc-prim- GHC primitives

Copyright(c) The University of Glasgow 2009
Licensesee libraries/ghc-prim/LICENSE
Portabilitynon-portable (GHC Extensions)
Safe HaskellNone




GHC type definitions. Use GHC.Exts from the base package instead of importing this module directly.



data Bool #



data Char #

The character type Char is an enumeration whose values represent Unicode (or equivalently ISO/IEC 10646) characters (see 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 toEnum and fromEnum from the Enum class respectively (or equivalently ord and chr).


C# Char# 

data Int #

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 minBound and maxBound from the Bounded class.


I# Int# 

data Word #

A Word is an unsigned integral type, with the same size as Int.


W# Word# 

data Float #

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.


F# Float# 

data Double #

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.


D# Double# 

data Ordering #



newtype IO a #

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.


IO (State# RealWorld -> (#State# RealWorld, a#)) 

isTrue# :: Int# -> Bool #

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

data SPEC #

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 Nat #

(Kind) This is the kind of type-level natural numbers.

data Symbol #

(Kind) This is the kind of type-level symbols. Declared here because class IP needs it

type family Any :: k where ... #

The type constructor Any is type to which you can unsafely coerce any lifted type, and back. More concretely, for a lifted type t and value x :: t, -- unsafeCoerce (unsafeCoerce x :: Any) :: t is equivalent to x.

class a ~~ b #

Lifted, heterogeneous equality. By lifted, we mean that it can be bogus (deferred type error). By heterogeneous, the two types a and b might have different kinds. Because ~~ can appear unexpectedly in error messages to users who do not care about the difference between heterogeneous equality ~~ and homogeneous equality ~, this is printed as ~ unless -fprint-equality-relations is set.

class Coercible a b #

Coercible is a two-parameter class that 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 Coercible 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 Safe Coercions by Joachim Breitner, Richard A. Eisenberg, Simon Peyton Jones and Stephanie Weirich.


data TYPE (a :: RuntimeRep) :: RuntimeRep -> * #

data RuntimeRep #

GHC maintains a property that the kind of all inhabited types (as distinct from type constructors or type-level data) tells us the runtime representation of values of that type. This datatype encodes the choice of runtime value. Note that TYPE is parameterised by RuntimeRep; this is precisely what we mean by the fact that a type's kind encodes the runtime representation.

For boxed values (that is, values that are represented by a pointer), a further distinction is made, between lifted types (that contain ⊥), and unlifted ones (that don't).


VecRep VecCount VecElem

a SIMD vector type

TupleRep [RuntimeRep]

An unboxed tuple of the given reps

SumRep [RuntimeRep]

An unboxed sum of the given reps


lifted; represented by a pointer


unlifted; represented by a pointer


signed, word-sized value


unsigned, word-sized value


signed, 64-bit value (on 32-bit only)


unsigned, 64-bit value (on 32-bit only)


A pointer, but not to a Haskell value


a 32-bit floating point number


a 64-bit floating point number

type Type = TYPE LiftedRep #

The kind of types with values. For example Int :: Type.

type * = TYPE LiftedRep #

A backward-compatible (pre-GHC 8.0) synonym for Type

type (★) = TYPE LiftedRep #

A unicode backward-compatible (pre-GHC 8.0) synonym for Type

data Constraint #

The kind of constraints, like Show a

data VecCount #

Length of a SIMD vector type



Runtime type representation

data Module #


Module TrName TrName 

data TrName #


TrNameS Addr# 
TrNameD [Char] 

data KindRep #

The representation produced by GHC for conjuring up the kind of a TypeRep.

type KindBndr = Int #

A de Bruijn index for a binder within a KindRep.