GHC.Utils.FV

Utilities for efficiently and deterministically computing free variables.

Deterministic free vars computations

type FV = InterestingVarFun -> VarSet -> VarAcc -> VarAcc

type InterestingVarFun = Var -> Bool

Predicate on possible free variables: returns True iff the variable is interesting

Running the computations

fvVarList :: FV -> [Var]

Run a free variable computation, returning a list of distinct free variables in deterministic order.

fvVarSet :: FV -> VarSet

Run a free variable computation, returning a non-deterministic set of free variables. Don't use if the set will be later converted to a list and the order of that list will impact the generated code.

fvDVarSet :: FV -> DVarSet

Run a free variable computation, returning a deterministic set of free variables. Note that this is just a wrapper around the version that returns a deterministic list. If you need a list you should use fvVarList.

Manipulating those computations

unitFV :: Id -> FV

Add a variable - when free, to the returned free variables. Ignores duplicates and respects the filtering function.

emptyFV :: FV

Return no free variables.

mkFVs :: [Var] -> FV

Add multiple variables - when free, to the returned free variables. Ignores duplicates and respects the filtering function.

unionFV :: FV -> FV -> FV

Union two free variable computations.

unionsFV :: [FV] -> FV

Union many free variable computations.

delFV :: Var -> FV -> FV

Mark the variable as not free by putting it in scope.

delFVs :: VarSet -> FV -> FV

Mark many free variables as not free.

filterFV :: InterestingVarFun -> FV -> FV

Filter a free variable computation.

mapUnionFV :: (a -> FV) -> [a] -> FV

Map a free variable computation over a list and union the results.