ghc-7.6.1.20121122: The GHC API

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InstEnv

Synopsis

Documentation

data OverlapFlag Source

Constructors

NoOverlap

This instance must not overlap another

Fields

isSafeOverlap :: Bool
 
OverlapOk

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

Example: constraint (Foo [Int]) instances (Foo [Int]) (Foo [a]) OverlapOk Since the second instance has the OverlapOk flag, the first instance will be chosen (otherwise its ambiguous which to choose)

Fields

isSafeOverlap :: Bool
 
Incoherent

Like OverlapOk, but also ignore this instance if it doesn't match the constraint you are trying to resolve, but could match if the type variables in the constraint were instantiated

Example: constraint (Foo [b]) instances (Foo [Int]) Incoherent (Foo [a]) Without the Incoherent flag, we'd complain that instantiating b would change which instance was chosen

Fields

isSafeOverlap :: Bool
 

type InstEnv = UniqFM ClsInstEnvSource

lookupUniqueInstEnv :: (InstEnv, InstEnv) -> 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'.