Constructors

The character typeChar is an enumeration whose values representUnicode (or equivalently ISO/IEC 10646) code points (i.e. characters, seehttp://www.unicode.org/ for details). This set extends the ISO 8859-1(Latin-1) character set (the first 256 characters), which is itself an extensionof the ASCII character set (the first 128 characters). A character literal inHaskell has typeChar.

To convert aChar to or from the correspondingInt value definedby Unicode, usetoEnum andfromEnum from theEnum class respectively (or equivalentlyord andchr).

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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 usingminBound andmaxBound from theBounded class.

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AWord is an unsigned integral type, with the same size asInt.

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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.

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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.

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A value of typeIO a is a computation which, when performed,does some I/O before returning a value of typea.

There is really only one way to "perform" an I/O action: bind it toMain.main in your program. When your program is run, the I/O willbe performed. It isn't possible to perform I/O from an arbitraryfunction, unless that function is itself in theIO monad and calledat some point, directly or indirectly, fromMain.main.

IO is a monad, soIO actions can be combined using either the do-notationor the>> and>>= operations from theMonad class.

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

SPEC is used by GHC in theSpecConstr 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 usingSPEC data type to inform which loops should be aggressively specialized.

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

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

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

Lifted, heterogeneous equality. By lifted, we mean that it can be bogus (deferred type error). By heterogeneous, the two typesa andb 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.

Coercible is a two-parameter class that has instances for typesa andb 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 ofCoercible 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, letD be a prototypical type constructor (data ornewtype) with three type arguments, which have rolesnominal,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 thenominal type arguments are equal, therepresentational type arguments can differ, but need to have aCoercible instance themself, and thephantom type arguments can be changed arbitrarily.

The third kind of instance exists for everynewtype 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 constructorMkNT is in scope.

If, as a library author of a type constructor likeSet a, you want to prevent a user of your module to writecoerce :: Set T -> Set NT, you need to set the role ofSet's type parameter tonominal, by writing

type role Set nominal

For more details about this feature, please refer toSafe Coercions by Joachim Breitner, Richard A. Eisenberg, Simon Peyton Jones and Stephanie Weirich.

Since: 4.7.0.0

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 thatTYPE is parameterised byRuntimeRep; 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).

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The kind of types with values. For exampleInt :: Type.

A backward-compatible (pre-GHC 8.0) synonym forType

A unicode backward-compatible (pre-GHC 8.0) synonym forType

The kind of constraints, likeShow a

Length of a SIMD vector type

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Element of a SIMD vector type

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The representation produced by GHC for conjuring up the kind of aTypeRep. See Note [Representing TyCon kinds: KindRep] in TcTypeable.

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A de Bruijn index for a binder within aKindRep.