ghc-tcplugins-extra-0.4.3: Utilities for writing GHC type-checker plugins
Copyright(C) 2015-2016 University of Twente
LicenseBSD2 (see the file LICENSE)
MaintainerChristiaan Baaij <>
Safe HaskellSafe-Inferred




Create new constraints

newWanted :: CtLoc -> PredType -> TcPluginM CtEvidence Source #

Create a new [W]anted constraint.

newGiven :: CtLoc -> PredType -> EvTerm -> TcPluginM CtEvidence Source #

Create a new [G]iven constraint, with the supplied evidence. This must not be invoked from tcPluginInit or tcPluginStop, or it will panic.

newDerived :: CtLoc -> PredType -> TcPluginM CtEvidence Source #

Create a new [D]erived constraint.

Creating evidence

evByFiat Source #


:: String

Name the coercion should have

-> Type

The LHS of the equivalence relation (~)

-> Type

The RHS of the equivalence relation (~)

-> EvTerm 

The EvTerm equivalent for unsafeCoerce


lookupModule Source #


:: ModuleName

Name of the module

-> FastString

Name of the package containing the module. NOTE: This value is ignored on ghc>=8.0.

-> TcPluginM Module 

Find a module

Trace state of the plugin

tracePlugin :: String -> TcPlugin -> TcPlugin Source #

Print out extra information about the initialisation, stop, and every run of the plugin when -ddump-tc-trace is enabled.


flattenGivens :: [Ct] -> [Ct] Source #

Flattens evidence of constraints by substituting each others equalities.

NB: Should only be used on [G]iven constraints!

NB: Doesn't flatten under binders

mkSubst :: Ct -> Maybe ((TcTyVar, TcType), Ct) Source #

Create simple substitution from type equalities

mkSubst' :: [Ct] -> [((TcTyVar, TcType), Ct)] Source #

Create flattened substitutions from type equalities, i.e. the substitutions have been applied to each others right hand sides.

substType :: [(TcTyVar, TcType)] -> TcType -> TcType Source #

Apply substitutions in Types

NB: Doesn't substitute under binders

substCt :: [(TcTyVar, TcType)] -> Ct -> Ct Source #

Apply substitution in the evidence of Cts