\begin{code}
mkSCC :: CostCentre -> Expr b -> Expr b
-- Note: Nested SCC's *are* preserved for the benefit of
- -- cost centre stack profiling (Durham)
-
-mkSCC cc (Lit lit) = Lit lit
-mkSCC cc (Lam x e) = Lam x (mkSCC cc e) -- Move _scc_ inside lambda
-mkSCC cc expr = Note (SCC cc) expr
+ -- cost centre stack profiling
+mkSCC cc (Lit lit) = Lit lit
+mkSCC cc (Lam x e) = Lam x (mkSCC cc e) -- Move _scc_ inside lambda
+mkSCC cc (Note (SCC cc') e) = Note (SCC cc) (Note (SCC cc') e)
+mkSCC cc (Note n e) = Note n (mkSCC cc e) -- Move _scc_ inside notes
+mkSCC cc expr = Note (SCC cc) expr
\end{code}