% $Id: Lift.lhs,v 1.23 2004/02/13 14:02:54 wlux Exp$ % % Copyright (c) 2001-2003, Wolfgang Lux % See LICENSE for the full license. % \nwfilename{Lift.lhs} \section{Lifting Declarations} After desugaring and simplifying the code, the compiler lifts all local function declarations to the top-level keeping only local variable declarations. The algorithm used here is similar to Johnsson's~\cite{Johnsson87:Thesis} (see also chapter 6 of~\cite{PeytonJonesLester92:Book}). It consists of two phases, first we abstract each local function declaration, adding its free variables as initial parameters and update all calls to take these variables into account. Then all local function declarations are collected and lifted to the top-level. \begin{verbatim} > module Transform.Lift (lift) where > import Control.Monad > import qualified Control.Monad.State as S > import Data.List > import qualified Data.Map as Map > import qualified Data.Set as Set > import Curry.Base.Ident > import Curry.Syntax > import Base.Eval (EvalEnv) > import Base.Expr > import Base.Value (ValueEnv, ValueInfo (..), lookupValue) > import Env.TopEnv > import Messages (internalError) > import SCC > import Types > lift :: ValueEnv -> EvalEnv -> Module -> (Module, ValueEnv, EvalEnv) > lift tyEnv evEnv (Module m es ds) = > (Module m es (concatMap liftFunDecl ds'),tyEnv',evEnv') > where (ds',tyEnv',evEnv') = > S.evalState (S.evalStateT (abstractModule m ds) tyEnv) evEnv \end{verbatim} \paragraph{Abstraction} Besides adding the free variables to every (local) function, the abstraction pass also has to update the type environment in order to reflect the new types of the expanded functions. As usual we use a state monad transformer in order to pass the type environment through. The environment constructed in the abstraction phase maps each local function declaration onto its replacement expression, i.e. the function applied to its free variables. \begin{verbatim} > type AbstractState a = S.StateT ValueEnv (S.State EvalEnv) a > type AbstractEnv = Map.Map Ident Expression > abstractModule :: ModuleIdent -> [Decl] > -> AbstractState ([Decl], ValueEnv, EvalEnv) > abstractModule m ds = > do > ds' <- mapM (abstractDecl m "" [] Map.empty) ds > tyEnv' <- S.get > evEnv' <- S.lift S.get > return (ds',tyEnv',evEnv') > abstractDecl :: ModuleIdent -> String -> [Ident] -> AbstractEnv -> Decl > -> AbstractState Decl > abstractDecl m _ lvs env (FunctionDecl p f eqs) = > liftM (FunctionDecl p f) (mapM (abstractEquation m lvs env) eqs) > abstractDecl m pre lvs env (PatternDecl p t rhs) = > liftM (PatternDecl p t) (abstractRhs m pre lvs env rhs) > abstractDecl _ _ _ _ d = return d > abstractEquation :: ModuleIdent -> [Ident] -> AbstractEnv -> Equation > -> AbstractState Equation > abstractEquation m lvs env (Equation p lhs@(FunLhs f ts) rhs) = > liftM (Equation p lhs) > (abstractRhs m (name f ++ ".") (lvs ++ bv ts) env rhs) > abstractEquation _ _ _ _ = error "Lift.abstractEquation: no pattern match" > abstractRhs :: ModuleIdent -> String -> [Ident] -> AbstractEnv -> Rhs > -> AbstractState Rhs > abstractRhs m pre lvs env (SimpleRhs p e _) = > liftM (flip (SimpleRhs p) []) (abstractExpr m pre lvs env e) > abstractRhs _ _ _ _ _ = error "Lift.abstractRhs: no pattern match" \end{verbatim} Within a declaration group we have to split the list of declarations into the function and value declarations. Only the function declarations are affected by the abstraction algorithm; the value declarations are left unchanged except for abstracting their right hand sides. The abstraction of a recursive declaration group is complicated by the fact that not all functions need to call each in a recursive declaration group. E.g., in the following example neither g nor h call each other. \begin{verbatim} f = g True where x = f 1 f z = y + z y = g False g z = if z then x else 0 \end{verbatim} Because of this fact, f and g can be abstracted separately by adding only \texttt{y} to \texttt{f} and \texttt{x} to \texttt{g}. On the other hand, in the following example \begin{verbatim} f x y = g 4 where g p = h p + x h q = k + y + q k = g x \end{verbatim} the local function \texttt{g} uses \texttt{h}, so the free variables of \texttt{h} have to be added to \texttt{g} as well. However, because \texttt{h} does not call \texttt{g} it is sufficient to add only \texttt{k} and \texttt{y} (and not \texttt{x}) to its definition. We handle this by computing the dependency graph between the functions and splitting this graph into its strongly connected components. Each component is then processed separately, adding the free variables in the group to its functions. We have to be careful with local declarations within desugared case expressions. If some of the cases have guards, e.g., \begin{verbatim} case e of x | x < 1 -> 1 x -> let double y = y * y in double x \end{verbatim} the desugarer at present may duplicate code. While there is no problem with local variable declaration being duplicated, we must avoid to lift local function declarations more than once. Therefore \texttt{abstractFunDecls} transforms only those function declarations that have not been lifted and discards the other declarations. Note that it is easy to check whether a function has been lifted by checking whether an entry for its untransformed name is still present in the type environment. \begin{verbatim} > abstractDeclGroup :: ModuleIdent -> String -> [Ident] -> AbstractEnv > -> [Decl] -> Expression -> AbstractState Expression > abstractDeclGroup m pre lvs env ds e = > abstractFunDecls m pre (lvs ++ bv vds) env (scc bv (qfv m) fds) vds e > where (fds,vds) = partition isFunDecl ds > abstractFunDecls :: ModuleIdent -> String -> [Ident] -> AbstractEnv > -> [[Decl]] -> [Decl] -> Expression > -> AbstractState Expression > abstractFunDecls m pre lvs env [] vds e = > do > vds' <- mapM (abstractDecl m pre lvs env) vds > e' <- abstractExpr m pre lvs env e > return (Let vds' e') > abstractFunDecls m pre lvs env (fds:fdss) vds e = > do > fs' <- liftM (\tyEnv -> filter (not . isLifted tyEnv) fs) S.get > S.modify (abstractFunTypes m pre fvs fs') > S.lift (S.modify (abstractFunAnnots m pre fs')) > fds' <- mapM (abstractFunDecl m pre fvs lvs env') > [d | d <- fds, any (elem fs') (bv d)] > e' <- abstractFunDecls m pre lvs env' fdss vds e > return (Let fds' e') > where fs = bv fds > fvs = filter (elem lvs) (Set.toList fvsRhs) > env' = foldr (bindF (map mkVar fvs)) env fs > fvsRhs = Set.unions > [Set.fromList (maybe [v] (qfv m) (Map.lookup v env)) | v <- qfv m fds] > bindF fvs' f = Map.insert f (apply (mkFun m pre f) fvs') > isLifted tyEnv f = null (lookupValue f tyEnv) > abstractFunTypes :: ModuleIdent -> String -> [Ident] -> [Ident] > -> ValueEnv -> ValueEnv > abstractFunTypes m pre fvs fs tyEnv = foldr abstractFunType tyEnv fs > where tys = map (varType tyEnv) fvs > abstractFunType f tyEnv' = > qualBindFun m (liftIdent pre f) > (foldr TypeArrow (varType tyEnv' f) tys) > (unbindFun f tyEnv') > abstractFunAnnots :: ModuleIdent -> String -> [Ident] -> EvalEnv -> EvalEnv > abstractFunAnnots _ pre fs evEnv = foldr abstractFunAnnot evEnv fs > where abstractFunAnnot f evEnv' = > case Map.lookup f evEnv' of > Just ev -> Map.insert (liftIdent pre f) ev (Map.delete f evEnv') > Nothing -> evEnv' > abstractFunDecl :: ModuleIdent -> String -> [Ident] -> [Ident] > -> AbstractEnv -> Decl -> AbstractState Decl > abstractFunDecl m pre fvs lvs env (FunctionDecl p f eqs) = > abstractDecl m pre lvs env (FunctionDecl p f' (map (addVars f') eqs)) > where f' = liftIdent pre f > addVars f1 (Equation p1 (FunLhs _ ts) rhs) = > Equation p1 (FunLhs f1 (map VariablePattern fvs ++ ts)) rhs > addVars _ _ = error "Lift.abstractFunDecl.addVars: no pattern match" > abstractFunDecl _ pre _ _ _ (ExternalDecl p cc ie f ty) = > return (ExternalDecl p cc ie (liftIdent pre f) ty) > abstractFunDecl _ _ _ _ _ _ = error "Lift.abstractFunDecl: no pattern match" > abstractExpr :: ModuleIdent -> String -> [Ident] -> AbstractEnv > -> Expression -> AbstractState Expression > abstractExpr _ _ _ _ (Literal l) = return (Literal l) > abstractExpr m pre lvs env (Variable v) > | isQualified v = return (Variable v) > | otherwise = maybe (return (Variable v)) (abstractExpr m pre lvs env) > (Map.lookup (unqualify v) env) > abstractExpr _ _ _ _ (Constructor c) = return (Constructor c) > abstractExpr m pre lvs env (Apply e1 e2) = > do > e1' <- abstractExpr m pre lvs env e1 > e2' <- abstractExpr m pre lvs env e2 > return (Apply e1' e2') > abstractExpr m pre lvs env (Let ds e) = abstractDeclGroup m pre lvs env ds e > abstractExpr m pre lvs env (Case r e alts) = > do > e' <- abstractExpr m pre lvs env e > alts' <- mapM (abstractAlt m pre lvs env) alts > return (Case r e' alts') > abstractExpr _ _ _ _ _ = internalError "abstractExpr" > abstractAlt :: ModuleIdent -> String -> [Ident] -> AbstractEnv -> Alt > -> AbstractState Alt > abstractAlt m pre lvs env (Alt p t rhs) = > liftM (Alt p t) (abstractRhs m pre (lvs ++ bv t) env rhs) \end{verbatim} \paragraph{Lifting} After the abstraction pass, all local function declarations are lifted to the top-level. \begin{verbatim} > liftFunDecl :: Decl -> [Decl] > liftFunDecl (FunctionDecl p f eqs) = (FunctionDecl p f eqs' : concat dss') > where (eqs',dss') = unzip (map liftEquation eqs) > liftFunDecl d = [d] > liftVarDecl :: Decl -> (Decl,[Decl]) > liftVarDecl (PatternDecl p t rhs) = (PatternDecl p t rhs',ds') > where (rhs',ds') = liftRhs rhs > liftVarDecl (ExtraVariables p vs) = (ExtraVariables p vs,[]) > liftVarDecl _ = error "Lift.liftVarDecl: no pattern match" > liftEquation :: Equation -> (Equation,[Decl]) > liftEquation (Equation p lhs rhs) = (Equation p lhs rhs',ds') > where (rhs',ds') = liftRhs rhs > liftRhs :: Rhs -> (Rhs,[Decl]) > liftRhs (SimpleRhs p e _) = (SimpleRhs p e' [],ds') > where (e',ds') = liftExpr e > liftRhs _ = error "Lift.liftRhs: no pattern match" > liftDeclGroup :: [Decl] -> ([Decl],[Decl]) > liftDeclGroup ds = (vds',concat (map liftFunDecl fds ++ dss')) > where (fds,vds) = partition isFunDecl ds > (vds',dss') = unzip (map liftVarDecl vds) > liftExpr :: Expression -> (Expression,[Decl]) > liftExpr (Literal l) = (Literal l,[]) > liftExpr (Variable v) = (Variable v,[]) > liftExpr (Constructor c) = (Constructor c,[]) > liftExpr (Apply e1 e2) = (Apply e1' e2',ds' ++ ds'') > where (e1',ds') = liftExpr e1 > (e2',ds'') = liftExpr e2 > liftExpr (Let ds e) = (mkLet ds' e',ds'' ++ ds''') > where (ds',ds'') = liftDeclGroup ds > (e',ds''') = liftExpr e > mkLet ds1 e1 = if null ds1 then e1 else Let ds1 e1 > liftExpr (Case r e alts) = (Case r e' alts',concat (ds':dss')) > where (e',ds') = liftExpr e > (alts',dss') = unzip (map liftAlt alts) > liftExpr _ = internalError "liftExpr" > liftAlt :: Alt -> (Alt,[Decl]) > liftAlt (Alt p t rhs) = (Alt p t rhs',ds') > where (rhs',ds') = liftRhs rhs \end{verbatim} \paragraph{Auxiliary definitions} \begin{verbatim} > isFunDecl :: Decl -> Bool > isFunDecl (FunctionDecl _ _ _) = True > isFunDecl (ExternalDecl _ _ _ _ _) = True > isFunDecl _ = False > mkFun :: ModuleIdent -> String -> Ident -> Expression > mkFun m pre f = Variable (qualifyWith m (liftIdent pre f)) > mkVar :: Ident -> Expression > mkVar v = Variable (qualify v) > apply :: Expression -> [Expression] -> Expression > apply = foldl Apply > qualBindFun :: ModuleIdent -> Ident -> Type -> ValueEnv -> ValueEnv > qualBindFun m f ty > = qualBindTopEnv "Lift.qualBindFun" f' (Value f' (polyType ty)) > where f' = qualifyWith m f > unbindFun :: Ident -> ValueEnv -> ValueEnv > unbindFun = unbindTopEnv > varType :: ValueEnv -> Ident -> Type > varType tyEnv v = > case lookupValue v tyEnv of > [Value _ (ForAll _ ty)] -> ty > _ -> internalError ("varType " ++ show v) > liftIdent :: String -> Ident -> Ident > liftIdent prefix x = > renameIdent (mkIdent (prefix ++ (show x))) (uniqueId x) > --renameIdent (mkIdent (prefix ++ name x ++ show (uniqueId x))) (uniqueId x) \end{verbatim}