matching and guards.
\begin{verbatim}
-sumif pred a b = if pred == Eq && a == b || pred == Neq && a != b
- then a + b
- else 0
+sumif cmp a b = if cmp == Eq && a == b
+ || cmp == Neq && a != b
+ then a + b
+ else 0
\end{verbatim}
\begin{verbatim}
-sumif pred a b = case pred of
+sumif cmp a b = case cmp of
Eq -> case a == b of
True -> a + b
False -> 0