ghc-7.10.1: The GHC API

Safe HaskellNone




data OverlapFlag Source

The semantics allowed for overlapping instances for a particular instance. See Note [Safe Haskell isSafeOverlap] (in lhs) for a explanation of the isSafeOverlap field.

data OverlapMode Source


NoOverlap SourceText

This instance must not overlap another NoOverlap instance. However, it may be overlapped by Overlapping instances, and it may overlap Overlappable instances.

Overlappable SourceText

Silently ignore this instance if you find a more specific one that matches the constraint you are trying to resolve

Example: constraint (Foo [Int]) instance Foo [Int] instance {--} Foo [a]

Since the second instance has the Overlappable flag, the first instance will be chosen (otherwise its ambiguous which to choose)

Overlapping SourceText

Silently ignore any more general instances that may be used to solve the constraint.

Example: constraint (Foo [Int]) instance {--} Foo [Int] instance Foo [a]

Since the first instance has the Overlapping flag, the second---more general---instance will be ignored (otherwise it is ambiguous which to choose)

Overlaps SourceText

Equivalent to having both Overlapping and Overlappable flags.

Incoherent SourceText

Behave like Overlappable and Overlapping, and in addition pick an an arbitrary one if there are multiple matching candidates, and don't worry about later instantiation

Example: constraint (Foo [b]) instance {-# INCOHERENT -} Foo [Int] instance Foo [a] Without the Incoherent flag, we'd complain that instantiating b would change which instance was chosen. See also note [Incoherent instances] in InstEnv

fuzzyClsInstCmp :: ClsInst -> ClsInst -> Ordering Source

A fuzzy comparison function for class instances, intended for sorting instances before displaying them to the user.

data IsOrphan Source

Is this instance an orphan? If it is not an orphan, contains an OccName witnessing the instance's non-orphanhood. See Note [Orphans]


NotOrphan OccName 

isOrphan :: IsOrphan -> Bool Source

Returns true if IsOrphan is orphan.

notOrphan :: IsOrphan -> Bool Source

Returns true if IsOrphan is not an orphan.

data InstEnvs Source

InstEnvs represents the combination of the global type class instance environment, the local type class instance environment, and the set of transitively reachable orphan modules (according to what modules have been directly imported) used to test orphan instance visibility.

type VisibleOrphanModules = ModuleSet Source

Set of visible orphan modules, according to what modules have been directly imported. This is based off of the dep_orphs field, which records transitively reachable orphan modules (modules that define orphan instances).

type InstEnv = UniqFM ClsInstEnv Source

identicalClsInstHead :: ClsInst -> ClsInst -> Bool Source

True when when the instance heads are the same e.g. both are Eq [(a,b)] Used for overriding in GHCi Obviously should be insenstive to alpha-renaming

lookupUniqueInstEnv :: InstEnvs -> Class -> [Type] -> Either MsgDoc (ClsInst, [Type]) Source

Look up an instance in the given instance environment. The given class application must match exactly one instance and the match may not contain any flexi type variables. If the lookup is unsuccessful, yield 'Left errorMessage'.

lookupInstEnv :: InstEnvs -> Class -> [Type] -> ClsInstLookupResult Source

See Note [Rules for instance lookup]

memberInstEnv :: InstEnv -> ClsInst -> Bool Source

Checks for an exact match of ClsInst in the instance environment. We use this when we do signature checking in TcRnDriver

instIsVisible :: VisibleOrphanModules -> ClsInst -> Bool Source

Test if an instance is visible, by checking that its origin module is in VisibleOrphanModules. See Note [Instance lookup and orphan instances]

orphNamesOfClsInst :: ClsInst -> NameSet Source

Collects the names of concrete types and type constructors that make up the head of a class instance. For instance, given `class Foo a b`:

`instance Foo (Either (Maybe Int) a) Bool` would yield [Either, Maybe, Int, Bool]

Used in the implementation of ":info" in GHCi.