id -package:llvm-hs-pure package:Cabal-syntax

Identity function.

id x = x

Identity functor and monad. (a non-strict monad)

A UnitId for a definite package. The DefUnitId invariant says that a UnitId identified this way is definite; i.e., it has no unfilled holes.

Identifies a fully instantiated component, which has been compiled and abbreviated as a hash. The embedded UnitId MUST NOT be for an indefinite component; an OpenUnitId is guaranteed not to have any holes.

Identifies a component which may have some unfilled holes; specifying its ComponentId and its OpenModuleSubst. TODO: Invariant that OpenModuleSubst is non-empty? See also the Text instance.

An OpenUnitId describes a (possibly partially) instantiated Backpack component, with a description of how the holes are filled in. Unlike OpenUnitId, the ModuleSubst is kept in a structured form that allows for substitution (which fills in holes.) This form of unit cannot be installed. It must first be converted to a UnitId. In the absence of Backpack, there are no holes to fill, so any such component always has an empty module substitution; thus we can lossily represent it as a 'DefiniteUnitId uid'. For a source component using Backpack, however, there is more structure as components may be parametrized over some signatures, and these "holes" may be partially or wholly filled. OpenUnitId plays an important role when we are mix-in linking, and is recorded to the installed packaged database for indefinite packages; however, for compiled packages that are fully instantiated, we instantiate OpenUnitId into UnitId. For more details see the Backpack spec https://github.com/ezyang/ghc-proposals/blob/backpack/proposals/0000-backpack.rst

When typechecking, we don't demand that a freshly instantiated IndefFullUnitId be compiled; instead, we just depend on the installed indefinite unit installed at the ComponentId.

Create a DefUnitId from a ComponentId and an instantiation with no holes.

Safe constructor from a UnitId. The only way to do this safely is if the instantiation is provided.

Get the set of holes (ModuleVar) embedded in a UnitId.

The class of monoids (types with an associative binary operation that has an identity). Instances should satisfy the following:

• Right identity x <> mempty = x
• Left identity mempty <> x = x
• Associativity x <> (y <> z) = (x <> y) <> z (Semigroup law)
• Concatenation mconcat = foldr (<>) mempty

The method names refer to the monoid of lists under concatenation, but there are many other instances. Some types can be viewed as a monoid in more than one way, e.g. both addition and multiplication on numbers. In such cases we often define newtypes and make those instances of Monoid, e.g. Sum and Product. NOTE: Semigroup is a superclass of Monoid since base-4.11.0.0.

Uninhabited data type

Deprecated: Don't leave me in the code

void value discards or ignores the result of evaluation, such as the return value of an IO action.

Examples

Replace the contents of a Maybe Int with unit:

>>> void Nothing
Nothing

>>> void (Just 3)
Just ()

Replace the contents of an Either Int Int with unit, resulting in an Either Int ():

>>> void (Left 8675309)
Left 8675309

>>> void (Right 8675309)
Right ()

Replace every element of a list with unit:

>>> void [1,2,3]
[(),(),()]

Replace the second element of a pair with unit:

>>> void (1,2)
(1,())

Discard the result of an IO action:

>>> mapM print [1,2]
1
2
[(),()]

>>> void $ mapM print [1,2]
1
2

Compiler flavour and version.

Field which is parsed but not pretty printed.

Field which can be define multiple times, and the results are mappended.

Monoidal field. Values are combined with mappend. Note: optionalFieldAla is a monoidalField with Last monoid.