diff --git a/src/Transfer/Core/Abs.hs b/src/Transfer/Core/Abs.hs
index dbc20b4bb..fd6a382b1 100644
--- a/src/Transfer/Core/Abs.hs
+++ b/src/Transfer/Core/Abs.hs
@@ -1,7 +1,8 @@
 {-# OPTIONS_GHC -fglasgow-exts #-}
-module Transfer.Core.Abs where
+module Transfer.Core.Abs (Tree(..), Module, Decl, ConsDecl, Pattern, FieldPattern, PatternVariable, Exp, LetDef, Case, FieldType, FieldValue, TMeta, CIdent, composOp, composOpM, composOpM_, composOpMPlus, composOpMonoid, composOpFold, compos, johnMajorEq) where
 
 import Control.Monad (ap,MonadPlus,msum,mplus,mzero)
+import Control.Monad.Identity
 import Data.Monoid
 
 -- Haskell module generated by the BNF converter
@@ -70,7 +71,10 @@ data Tree :: * -> * where
     CIdent :: String -> Tree CIdent_
 
 composOp :: (forall a. Tree a -> Tree a) -> Tree c -> Tree c
-composOp f = head . composOpM (\x -> [f x])
+composOp f = runIdentity . composOpM (Identity . f)
+
+composOpM :: Monad m => (forall a. Tree a -> m (Tree a)) -> Tree c -> m (Tree c)
+composOpM = compos return ap
 
 composOpM_ :: Monad m => (forall a. Tree a -> m ()) -> Tree c -> m ()
 composOpM_ = composOpFold (return ()) (>>)
@@ -81,61 +85,39 @@ composOpMPlus = composOpFold mzero mplus
 composOpMonoid :: Monoid m => (forall a. Tree a -> m) -> Tree c -> m
 composOpMonoid = composOpFold mempty mappend
 
-composOpM :: Monad m => (forall a. Tree a -> m (Tree a)) -> Tree c -> m (Tree c)
-composOpM f t = case t of
-    Module decls -> return Module `ap` mapM f decls
-    DataDecl cident exp consdecls -> return DataDecl `ap` f cident `ap` f exp `ap` mapM f consdecls
-    TypeDecl cident exp -> return TypeDecl `ap` f cident `ap` f exp
-    ValueDecl cident exp -> return ValueDecl `ap` f cident `ap` f exp
-    ConsDecl cident exp -> return ConsDecl `ap` f cident `ap` f exp
-    PCons cident patterns -> return PCons `ap` f cident `ap` mapM f patterns
-    PVar patternvariable -> return PVar `ap` f patternvariable
-    PRec fieldpatterns -> return PRec `ap` mapM f fieldpatterns
-    FieldPattern cident pattern -> return FieldPattern `ap` f cident `ap` f pattern
-    PVVar cident -> return PVVar `ap` f cident
-    ELet letdefs exp -> return ELet `ap` mapM f letdefs `ap` f exp
-    ECase exp cases -> return ECase `ap` f exp `ap` mapM f cases
-    EAbs patternvariable exp -> return EAbs `ap` f patternvariable `ap` f exp
-    EPi patternvariable exp0 exp1 -> return EPi `ap` f patternvariable `ap` f exp0 `ap` f exp1
-    EApp exp0 exp1 -> return EApp `ap` f exp0 `ap` f exp1
-    EProj exp cident -> return EProj `ap` f exp `ap` f cident
-    ERecType fieldtypes -> return ERecType `ap` mapM f fieldtypes
-    ERec fieldvalues -> return ERec `ap` mapM f fieldvalues
-    EVar cident -> return EVar `ap` f cident
-    EMeta tmeta -> return EMeta `ap` f tmeta
-    LetDef cident exp -> return LetDef `ap` f cident `ap` f exp
-    Case pattern exp0 exp1 -> return Case `ap` f pattern `ap` f exp0 `ap` f exp1
-    FieldType cident exp -> return FieldType `ap` f cident `ap` f exp
-    FieldValue cident exp -> return FieldValue `ap` f cident `ap` f exp
-    _ -> return t
-
+newtype C b a = C { unC :: b }
 composOpFold :: b -> (b -> b -> b) -> (forall a. Tree a -> b) -> Tree c -> b
-composOpFold zero combine f t = case t of
-    Module decls -> foldr combine zero (map f decls)
-    DataDecl cident exp consdecls -> f cident `combine` f exp `combine` foldr combine zero (map f consdecls)
-    TypeDecl cident exp -> f cident `combine` f exp
-    ValueDecl cident exp -> f cident `combine` f exp
-    ConsDecl cident exp -> f cident `combine` f exp
-    PCons cident patterns -> f cident `combine` foldr combine zero (map f patterns)
-    PVar patternvariable -> f patternvariable
-    PRec fieldpatterns -> foldr combine zero (map f fieldpatterns)
-    FieldPattern cident pattern -> f cident `combine` f pattern
-    PVVar cident -> f cident
-    ELet letdefs exp -> foldr combine zero (map f letdefs) `combine` f exp
-    ECase exp cases -> f exp `combine` foldr combine zero (map f cases)
-    EAbs patternvariable exp -> f patternvariable `combine` f exp
-    EPi patternvariable exp0 exp1 -> f patternvariable `combine` f exp0 `combine` f exp1
-    EApp exp0 exp1 -> f exp0 `combine` f exp1
-    EProj exp cident -> f exp `combine` f cident
-    ERecType fieldtypes -> foldr combine zero (map f fieldtypes)
-    ERec fieldvalues -> foldr combine zero (map f fieldvalues)
-    EVar cident -> f cident
-    EMeta tmeta -> f tmeta
-    LetDef cident exp -> f cident `combine` f exp
-    Case pattern exp0 exp1 -> f pattern `combine` f exp0 `combine` f exp1
-    FieldType cident exp -> f cident `combine` f exp
-    FieldValue cident exp -> f cident `combine` f exp
-    _ -> zero
+composOpFold z c f = unC . compos (\_ -> C z) (\(C x) (C y) -> C (c x y)) (C . f)
+
+compos :: (forall a. a -> m a) 
+       -> (forall a b. m (a -> b) -> m a -> m b) 
+       -> (forall a. Tree a -> m (Tree a)) -> Tree c -> m (Tree c)
+compos r a f t = case t of
+    Module decls -> r Module `a` foldr (a . a (r (:)) . f) (r []) decls
+    DataDecl cident exp consdecls -> r DataDecl `a` f cident `a` f exp `a` foldr (a . a (r (:)) . f) (r []) consdecls
+    TypeDecl cident exp -> r TypeDecl `a` f cident `a` f exp
+    ValueDecl cident exp -> r ValueDecl `a` f cident `a` f exp
+    ConsDecl cident exp -> r ConsDecl `a` f cident `a` f exp
+    PCons cident patterns -> r PCons `a` f cident `a` foldr (a . a (r (:)) . f) (r []) patterns
+    PVar patternvariable -> r PVar `a` f patternvariable
+    PRec fieldpatterns -> r PRec `a` foldr (a . a (r (:)) . f) (r []) fieldpatterns
+    FieldPattern cident pattern -> r FieldPattern `a` f cident `a` f pattern
+    PVVar cident -> r PVVar `a` f cident
+    ELet letdefs exp -> r ELet `a` foldr (a . a (r (:)) . f) (r []) letdefs `a` f exp
+    ECase exp cases -> r ECase `a` f exp `a` foldr (a . a (r (:)) . f) (r []) cases
+    EAbs patternvariable exp -> r EAbs `a` f patternvariable `a` f exp
+    EPi patternvariable exp0 exp1 -> r EPi `a` f patternvariable `a` f exp0 `a` f exp1
+    EApp exp0 exp1 -> r EApp `a` f exp0 `a` f exp1
+    EProj exp cident -> r EProj `a` f exp `a` f cident
+    ERecType fieldtypes -> r ERecType `a` foldr (a . a (r (:)) . f) (r []) fieldtypes
+    ERec fieldvalues -> r ERec `a` foldr (a . a (r (:)) . f) (r []) fieldvalues
+    EVar cident -> r EVar `a` f cident
+    EMeta tmeta -> r EMeta `a` f tmeta
+    LetDef cident exp -> r LetDef `a` f cident `a` f exp
+    Case pattern exp0 exp1 -> r Case `a` f pattern `a` f exp0 `a` f exp1
+    FieldType cident exp -> r FieldType `a` f cident `a` f exp
+    FieldValue cident exp -> r FieldValue `a` f cident `a` f exp
+    _ -> r t
 
 instance Show (Tree c) where
   showsPrec n t = case t of
diff --git a/src/Transfer/Syntax/Abs.hs b/src/Transfer/Syntax/Abs.hs
index 9883433eb..cf54d5569 100644
--- a/src/Transfer/Syntax/Abs.hs
+++ b/src/Transfer/Syntax/Abs.hs
@@ -1,7 +1,8 @@
 {-# OPTIONS_GHC -fglasgow-exts #-}
-module Transfer.Syntax.Abs where
+module Transfer.Syntax.Abs (Tree(..), Module, Import, Decl, ConsDecl, Guard, Pattern, CommaPattern, FieldPattern, Exp, VarOrWild, LetDef, Case, Bind, FieldType, FieldValue, Ident, composOp, composOpM, composOpM_, composOpMPlus, composOpMonoid, composOpFold, compos, johnMajorEq) where
 
 import Control.Monad (ap,MonadPlus,msum,mplus,mzero)
+import Control.Monad.Identity
 import Data.Monoid
 
 -- Haskell module generated by the BNF converter
@@ -112,7 +113,10 @@ data Tree :: * -> * where
     Ident :: String -> Tree Ident_
 
 composOp :: (forall a. Tree a -> Tree a) -> Tree c -> Tree c
-composOp f = head . composOpM (\x -> [f x])
+composOp f = runIdentity . composOpM (Identity . f)
+
+composOpM :: Monad m => (forall a. Tree a -> m (Tree a)) -> Tree c -> m (Tree c)
+composOpM = compos return ap
 
 composOpM_ :: Monad m => (forall a. Tree a -> m ()) -> Tree c -> m ()
 composOpM_ = composOpFold (return ()) (>>)
@@ -123,125 +127,71 @@ composOpMPlus = composOpFold mzero mplus
 composOpMonoid :: Monoid m => (forall a. Tree a -> m) -> Tree c -> m
 composOpMonoid = composOpFold mempty mappend
 
-composOpM :: Monad m => (forall a. Tree a -> m (Tree a)) -> Tree c -> m (Tree c)
-composOpM f t = case t of
-    Module imports decls -> return Module `ap` mapM f imports `ap` mapM f decls
-    Import i -> return Import `ap` f i
-    DataDecl i exp consdecls -> return DataDecl `ap` f i `ap` f exp `ap` mapM f consdecls
-    TypeDecl i exp -> return TypeDecl `ap` f i `ap` f exp
-    ValueDecl i patterns guard exp -> return ValueDecl `ap` f i `ap` mapM f patterns `ap` f guard `ap` f exp
-    DeriveDecl i0 i1 -> return DeriveDecl `ap` f i0 `ap` f i1
-    ConsDecl i exp -> return ConsDecl `ap` f i `ap` f exp
-    GuardExp exp -> return GuardExp `ap` f exp
-    POr pattern0 pattern1 -> return POr `ap` f pattern0 `ap` f pattern1
-    PListCons pattern0 pattern1 -> return PListCons `ap` f pattern0 `ap` f pattern1
-    PConsTop i pattern patterns -> return PConsTop `ap` f i `ap` f pattern `ap` mapM f patterns
-    PCons i patterns -> return PCons `ap` f i `ap` mapM f patterns
-    PRec fieldpatterns -> return PRec `ap` mapM f fieldpatterns
-    PList commapatterns -> return PList `ap` mapM f commapatterns
-    PTuple commapattern commapatterns -> return PTuple `ap` f commapattern `ap` mapM f commapatterns
-    PVar i -> return PVar `ap` f i
-    CommaPattern pattern -> return CommaPattern `ap` f pattern
-    FieldPattern i pattern -> return FieldPattern `ap` f i `ap` f pattern
-    EPi varorwild exp0 exp1 -> return EPi `ap` f varorwild `ap` f exp0 `ap` f exp1
-    EPiNoVar exp0 exp1 -> return EPiNoVar `ap` f exp0 `ap` f exp1
-    EAbs varorwild exp -> return EAbs `ap` f varorwild `ap` f exp
-    ELet letdefs exp -> return ELet `ap` mapM f letdefs `ap` f exp
-    ECase exp cases -> return ECase `ap` f exp `ap` mapM f cases
-    EIf exp0 exp1 exp2 -> return EIf `ap` f exp0 `ap` f exp1 `ap` f exp2
-    EDo binds exp -> return EDo `ap` mapM f binds `ap` f exp
-    EBind exp0 exp1 -> return EBind `ap` f exp0 `ap` f exp1
-    EBindC exp0 exp1 -> return EBindC `ap` f exp0 `ap` f exp1
-    EOr exp0 exp1 -> return EOr `ap` f exp0 `ap` f exp1
-    EAnd exp0 exp1 -> return EAnd `ap` f exp0 `ap` f exp1
-    EEq exp0 exp1 -> return EEq `ap` f exp0 `ap` f exp1
-    ENe exp0 exp1 -> return ENe `ap` f exp0 `ap` f exp1
-    ELt exp0 exp1 -> return ELt `ap` f exp0 `ap` f exp1
-    ELe exp0 exp1 -> return ELe `ap` f exp0 `ap` f exp1
-    EGt exp0 exp1 -> return EGt `ap` f exp0 `ap` f exp1
-    EGe exp0 exp1 -> return EGe `ap` f exp0 `ap` f exp1
-    EListCons exp0 exp1 -> return EListCons `ap` f exp0 `ap` f exp1
-    EAdd exp0 exp1 -> return EAdd `ap` f exp0 `ap` f exp1
-    ESub exp0 exp1 -> return ESub `ap` f exp0 `ap` f exp1
-    EMul exp0 exp1 -> return EMul `ap` f exp0 `ap` f exp1
-    EDiv exp0 exp1 -> return EDiv `ap` f exp0 `ap` f exp1
-    EMod exp0 exp1 -> return EMod `ap` f exp0 `ap` f exp1
-    ENeg exp -> return ENeg `ap` f exp
-    EApp exp0 exp1 -> return EApp `ap` f exp0 `ap` f exp1
-    EProj exp i -> return EProj `ap` f exp `ap` f i
-    ERecType fieldtypes -> return ERecType `ap` mapM f fieldtypes
-    ERec fieldvalues -> return ERec `ap` mapM f fieldvalues
-    EList exps -> return EList `ap` mapM f exps
-    ETuple exp exps -> return ETuple `ap` f exp `ap` mapM f exps
-    EVar i -> return EVar `ap` f i
-    VVar i -> return VVar `ap` f i
-    LetDef i exp -> return LetDef `ap` f i `ap` f exp
-    Case pattern guard exp -> return Case `ap` f pattern `ap` f guard `ap` f exp
-    BindVar varorwild exp -> return BindVar `ap` f varorwild `ap` f exp
-    BindNoVar exp -> return BindNoVar `ap` f exp
-    FieldType i exp -> return FieldType `ap` f i `ap` f exp
-    FieldValue i exp -> return FieldValue `ap` f i `ap` f exp
-    _ -> return t
-
+newtype C b a = C { unC :: b }
 composOpFold :: b -> (b -> b -> b) -> (forall a. Tree a -> b) -> Tree c -> b
-composOpFold zero combine f t = case t of
-    Module imports decls -> foldr combine zero (map f imports) `combine` foldr combine zero (map f decls)
-    Import i -> f i
-    DataDecl i exp consdecls -> f i `combine` f exp `combine` foldr combine zero (map f consdecls)
-    TypeDecl i exp -> f i `combine` f exp
-    ValueDecl i patterns guard exp -> f i `combine` foldr combine zero (map f patterns) `combine` f guard `combine` f exp
-    DeriveDecl i0 i1 -> f i0 `combine` f i1
-    ConsDecl i exp -> f i `combine` f exp
-    GuardExp exp -> f exp
-    POr pattern0 pattern1 -> f pattern0 `combine` f pattern1
-    PListCons pattern0 pattern1 -> f pattern0 `combine` f pattern1
-    PConsTop i pattern patterns -> f i `combine` f pattern `combine` foldr combine zero (map f patterns)
-    PCons i patterns -> f i `combine` foldr combine zero (map f patterns)
-    PRec fieldpatterns -> foldr combine zero (map f fieldpatterns)
-    PList commapatterns -> foldr combine zero (map f commapatterns)
-    PTuple commapattern commapatterns -> f commapattern `combine` foldr combine zero (map f commapatterns)
-    PVar i -> f i
-    CommaPattern pattern -> f pattern
-    FieldPattern i pattern -> f i `combine` f pattern
-    EPi varorwild exp0 exp1 -> f varorwild `combine` f exp0 `combine` f exp1
-    EPiNoVar exp0 exp1 -> f exp0 `combine` f exp1
-    EAbs varorwild exp -> f varorwild `combine` f exp
-    ELet letdefs exp -> foldr combine zero (map f letdefs) `combine` f exp
-    ECase exp cases -> f exp `combine` foldr combine zero (map f cases)
-    EIf exp0 exp1 exp2 -> f exp0 `combine` f exp1 `combine` f exp2
-    EDo binds exp -> foldr combine zero (map f binds) `combine` f exp
-    EBind exp0 exp1 -> f exp0 `combine` f exp1
-    EBindC exp0 exp1 -> f exp0 `combine` f exp1
-    EOr exp0 exp1 -> f exp0 `combine` f exp1
-    EAnd exp0 exp1 -> f exp0 `combine` f exp1
-    EEq exp0 exp1 -> f exp0 `combine` f exp1
-    ENe exp0 exp1 -> f exp0 `combine` f exp1
-    ELt exp0 exp1 -> f exp0 `combine` f exp1
-    ELe exp0 exp1 -> f exp0 `combine` f exp1
-    EGt exp0 exp1 -> f exp0 `combine` f exp1
-    EGe exp0 exp1 -> f exp0 `combine` f exp1
-    EListCons exp0 exp1 -> f exp0 `combine` f exp1
-    EAdd exp0 exp1 -> f exp0 `combine` f exp1
-    ESub exp0 exp1 -> f exp0 `combine` f exp1
-    EMul exp0 exp1 -> f exp0 `combine` f exp1
-    EDiv exp0 exp1 -> f exp0 `combine` f exp1
-    EMod exp0 exp1 -> f exp0 `combine` f exp1
-    ENeg exp -> f exp
-    EApp exp0 exp1 -> f exp0 `combine` f exp1
-    EProj exp i -> f exp `combine` f i
-    ERecType fieldtypes -> foldr combine zero (map f fieldtypes)
-    ERec fieldvalues -> foldr combine zero (map f fieldvalues)
-    EList exps -> foldr combine zero (map f exps)
-    ETuple exp exps -> f exp `combine` foldr combine zero (map f exps)
-    EVar i -> f i
-    VVar i -> f i
-    LetDef i exp -> f i `combine` f exp
-    Case pattern guard exp -> f pattern `combine` f guard `combine` f exp
-    BindVar varorwild exp -> f varorwild `combine` f exp
-    BindNoVar exp -> f exp
-    FieldType i exp -> f i `combine` f exp
-    FieldValue i exp -> f i `combine` f exp
-    _ -> zero
+composOpFold z c f = unC . compos (\_ -> C z) (\(C x) (C y) -> C (c x y)) (C . f)
+
+compos :: (forall a. a -> m a) 
+       -> (forall a b. m (a -> b) -> m a -> m b) 
+       -> (forall a. Tree a -> m (Tree a)) -> Tree c -> m (Tree c)
+compos r a f t = case t of
+    Module imports decls -> r Module `a` foldr (a . a (r (:)) . f) (r []) imports `a` foldr (a . a (r (:)) . f) (r []) decls
+    Import i -> r Import `a` f i
+    DataDecl i exp consdecls -> r DataDecl `a` f i `a` f exp `a` foldr (a . a (r (:)) . f) (r []) consdecls
+    TypeDecl i exp -> r TypeDecl `a` f i `a` f exp
+    ValueDecl i patterns guard exp -> r ValueDecl `a` f i `a` foldr (a . a (r (:)) . f) (r []) patterns `a` f guard `a` f exp
+    DeriveDecl i0 i1 -> r DeriveDecl `a` f i0 `a` f i1
+    ConsDecl i exp -> r ConsDecl `a` f i `a` f exp
+    GuardExp exp -> r GuardExp `a` f exp
+    POr pattern0 pattern1 -> r POr `a` f pattern0 `a` f pattern1
+    PListCons pattern0 pattern1 -> r PListCons `a` f pattern0 `a` f pattern1
+    PConsTop i pattern patterns -> r PConsTop `a` f i `a` f pattern `a` foldr (a . a (r (:)) . f) (r []) patterns
+    PCons i patterns -> r PCons `a` f i `a` foldr (a . a (r (:)) . f) (r []) patterns
+    PRec fieldpatterns -> r PRec `a` foldr (a . a (r (:)) . f) (r []) fieldpatterns
+    PList commapatterns -> r PList `a` foldr (a . a (r (:)) . f) (r []) commapatterns
+    PTuple commapattern commapatterns -> r PTuple `a` f commapattern `a` foldr (a . a (r (:)) . f) (r []) commapatterns
+    PVar i -> r PVar `a` f i
+    CommaPattern pattern -> r CommaPattern `a` f pattern
+    FieldPattern i pattern -> r FieldPattern `a` f i `a` f pattern
+    EPi varorwild exp0 exp1 -> r EPi `a` f varorwild `a` f exp0 `a` f exp1
+    EPiNoVar exp0 exp1 -> r EPiNoVar `a` f exp0 `a` f exp1
+    EAbs varorwild exp -> r EAbs `a` f varorwild `a` f exp
+    ELet letdefs exp -> r ELet `a` foldr (a . a (r (:)) . f) (r []) letdefs `a` f exp
+    ECase exp cases -> r ECase `a` f exp `a` foldr (a . a (r (:)) . f) (r []) cases
+    EIf exp0 exp1 exp2 -> r EIf `a` f exp0 `a` f exp1 `a` f exp2
+    EDo binds exp -> r EDo `a` foldr (a . a (r (:)) . f) (r []) binds `a` f exp
+    EBind exp0 exp1 -> r EBind `a` f exp0 `a` f exp1
+    EBindC exp0 exp1 -> r EBindC `a` f exp0 `a` f exp1
+    EOr exp0 exp1 -> r EOr `a` f exp0 `a` f exp1
+    EAnd exp0 exp1 -> r EAnd `a` f exp0 `a` f exp1
+    EEq exp0 exp1 -> r EEq `a` f exp0 `a` f exp1
+    ENe exp0 exp1 -> r ENe `a` f exp0 `a` f exp1
+    ELt exp0 exp1 -> r ELt `a` f exp0 `a` f exp1
+    ELe exp0 exp1 -> r ELe `a` f exp0 `a` f exp1
+    EGt exp0 exp1 -> r EGt `a` f exp0 `a` f exp1
+    EGe exp0 exp1 -> r EGe `a` f exp0 `a` f exp1
+    EListCons exp0 exp1 -> r EListCons `a` f exp0 `a` f exp1
+    EAdd exp0 exp1 -> r EAdd `a` f exp0 `a` f exp1
+    ESub exp0 exp1 -> r ESub `a` f exp0 `a` f exp1
+    EMul exp0 exp1 -> r EMul `a` f exp0 `a` f exp1
+    EDiv exp0 exp1 -> r EDiv `a` f exp0 `a` f exp1
+    EMod exp0 exp1 -> r EMod `a` f exp0 `a` f exp1
+    ENeg exp -> r ENeg `a` f exp
+    EApp exp0 exp1 -> r EApp `a` f exp0 `a` f exp1
+    EProj exp i -> r EProj `a` f exp `a` f i
+    ERecType fieldtypes -> r ERecType `a` foldr (a . a (r (:)) . f) (r []) fieldtypes
+    ERec fieldvalues -> r ERec `a` foldr (a . a (r (:)) . f) (r []) fieldvalues
+    EList exps -> r EList `a` foldr (a . a (r (:)) . f) (r []) exps
+    ETuple exp exps -> r ETuple `a` f exp `a` foldr (a . a (r (:)) . f) (r []) exps
+    EVar i -> r EVar `a` f i
+    VVar i -> r VVar `a` f i
+    LetDef i exp -> r LetDef `a` f i `a` f exp
+    Case pattern guard exp -> r Case `a` f pattern `a` f guard `a` f exp
+    BindVar varorwild exp -> r BindVar `a` f varorwild `a` f exp
+    BindNoVar exp -> r BindNoVar `a` f exp
+    FieldType i exp -> r FieldType `a` f i `a` f exp
+    FieldValue i exp -> r FieldValue `a` f i `a` f exp
+    _ -> r t
 
 instance Show (Tree c) where
   showsPrec n t = case t of