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Diffstat (limited to 'Library/Term.hs')
| -rw-r--r-- | Library/Term.hs | 193 |
1 files changed, 193 insertions, 0 deletions
diff --git a/Library/Term.hs b/Library/Term.hs new file mode 100644 index 0000000..029af7e --- /dev/null +++ b/Library/Term.hs @@ -0,0 +1,193 @@ +module Library.Term ( + Term(..), + Substitution, + + alphaEquiv, + alphaConvert, + alphaConvertList, + substitute, + boundVars, + freeVars, + rename, + typeOf, + typeVarsInTerm, + mkEquals, + isEq, + getlhs, + getrhs + ) where + + + +import Data.List +import qualified Data.Set as Set +import qualified Data.Map as Map +import Library.TypeVar + + + +data Term = TVar { tVar :: Var } + | TConst { tConst :: Const + , tConstType :: Type } + | TApp { tAppLeft :: Term + , tAppRight :: Term } + | TAbs { tAbsVar :: Term + , tAbsTerm :: Term } deriving (Ord) + +type Substitution = ( [(Name,Type)], [(Var,Term)] ) + + +instance Show Term where + show (TVar a) = show a + show (TConst a _) = show a + show (TApp (TApp eq lhs) rhs) + | isEq eq = "(" ++ (show lhs) ++ " = " ++ (show rhs) ++ ")" + show (TApp a b) = "(" ++ (show a) ++ " " ++ (show b) ++ ")" + show (TAbs a b) = "(\\" ++ (show a) ++ " -> " ++ (show b) ++ ")" + + +instance Eq Term where + a == b = a `alphaEquiv` b + + + +alphaEquiv :: Term -> Term -> Bool +alphaEquiv a b = + let equiv = \term1 term2 varmap1 varmap2 depth -> + case (term1,term2) of + (TConst a1 b1, TConst a2 b2) -> + a1 == a2 && b1 == b2 + + (TApp a1 b1, TApp a2 b2) -> + equiv a1 a2 varmap1 varmap2 depth && + equiv b1 b2 varmap1 varmap2 depth + + (TAbs (TVar (Var name1 type1)) b1, TAbs (TVar (Var name2 type2)) b2) -> + type1 == type2 && + equiv b1 b2 newmap1 newmap2 (depth+1) + where newmap1 = Map.insert (Var name1 type1) depth varmap1 + newmap2 = Map.insert (Var name2 type2) depth varmap2 + + (TVar a1, TVar a2) -> + a1 == a2 && Map.notMember a1 varmap1 && Map.notMember a2 varmap2 || + Map.lookup a1 varmap1 == Map.lookup a2 varmap2 + + (_,_) -> False + in equiv a b Map.empty Map.empty 0 + + +alphaConvert :: Term -> Term -> Term +alphaConvert (TConst a ty) (TConst _ _) = TConst a ty +alphaConvert (TApp a1 b1) (TApp a2 b2) = TApp (alphaConvert a1 a2) (alphaConvert b1 b2) +alphaConvert (TVar v) (TVar _) = TVar v +alphaConvert (TAbs v1 a) (TAbs v2 b) = substitute ([],[(tVar v1,v2)]) (TAbs v1 (alphaConvert a b)) + + +alphaConvertList :: [Term] -> [Term] -> [Term] +alphaConvertList a b = map (\x -> alphaConvert (fst x) (snd x)) (zip a b) + + +substitute :: Substitution -> Term -> Term +substitute (tymap,vmap) term = + let typesub = + (\x y -> + case y of + (TConst a ty) -> if (ty == (TypeVar . fst $ x)) + then TConst a (snd x) + else TConst a ty + (TApp a b) -> TApp (typesub x a) (typesub x b) + (TAbs (TVar (Var n ty)) a) -> if (ty == (TypeVar . fst $ x)) + then TAbs (TVar (Var n (snd x))) (typesub x a) + else TAbs (TVar (Var n ty)) (typesub x a) + (TVar (Var n ty)) -> if (ty == (TypeVar . fst $ x)) + then TVar (Var n (snd x)) + else TVar (Var n ty)) + varsub = + (\x y -> + case y of + (TConst a ty) -> TConst a ty + (TApp a b) -> TApp (varsub x a) (varsub x b) + (TVar v) -> if (v == (fst x)) + then snd x + else TVar v + (TAbs v a) -> let safe = rename (TAbs v a) (Set.insert (fst x) (freeVars . snd $ x)) + in case safe of + (TAbs m n) -> TAbs m (varsub x n)) + tydone = foldl' (\x y -> typesub y x) term tymap + vdone = foldl' (\x y -> varsub y x) tydone vmap + in vdone + + +boundVars :: Term -> Set.Set Var +boundVars (TConst a b) = Set.empty +boundVars (TApp a b) = Set.union (boundVars a) (boundVars b) +boundVars (TVar a) = Set.empty +boundVars (TAbs a b) = Set.insert (tVar a) (boundVars b) + + +freeVars :: Term -> Set.Set Var +freeVars (TConst a b) = Set.empty +freeVars (TApp a b) = Set.union (freeVars a) (freeVars b) +freeVars (TVar a) = Set.singleton a +freeVars (TAbs a b) = Set.delete (tVar a) (freeVars b) + + +rename :: Term -> Set.Set Var -> Term +rename (TAbs (TVar v) t) vars = + let doRename = + (\x y z -> case x of + (TAbs (TVar a) b) -> if (a == y) + then TAbs (TVar z) (doRename b y z) + else TAbs (TVar a) (doRename b y z) + (TConst a b) -> TConst a b + (TApp a b) -> TApp (doRename a y z) (doRename b y z) + (TVar a) -> if (a == y) + then TVar z + else TVar a) + findSafe = + (\x y -> if (Set.member x y) + then case x of + (Var a b) -> + case a of + (Name c d) -> findSafe (Var (Name c (d ++ "'")) b) y + else x) + in if (Set.member v vars) + then doRename (TAbs (TVar v) t) v (findSafe v vars) + else TAbs (TVar v) t + + +typeOf :: Term -> Type +typeOf (TConst _ ty) = ty +typeOf (TVar v) = varTy v +typeOf (TAbs v t) = typeFunc (typeOf v) (typeOf t) +typeOf (TApp f _) = + -- type of f is of the form [[a,b], "->"] + last . aType . typeOf $ f + + +typeVarsInTerm :: Term -> Set.Set Type +typeVarsInTerm (TConst _ ty) = typeVarsInType ty +typeVarsInTerm (TVar v) = typeVarsInType . varTy $ v +typeVarsInTerm (TAbs v t) = Set.union (typeVarsInType . varTy . tVar $ v) (typeVarsInTerm t) +typeVarsInTerm (TApp f x) = Set.union (typeVarsInTerm f) (typeVarsInTerm x) + + +mkEquals :: Term -> Term -> Term +mkEquals lhs rhs = + let eqConst = TConst (Const (Name [] "=")) (mkEqualsType (typeOf lhs)) + in TApp (TApp eqConst lhs) rhs + + +getlhs :: Term -> Term +getlhs (TApp (TApp eq lhs) _) + | (isEq eq) = lhs + + +getrhs :: Term -> Term +getrhs (TApp (TApp eq _) rhs) + | (isEq eq) = rhs + + +isEq :: Term -> Bool +isEq (TConst (Const (Name [] "=")) _) = True +isEq _ = False |