Add minBy and maxBy to Util

src/Util.md

@@ -16,6 +16,44 @@ import Data.Fin
 %default total
 ```
 
+## Foldable
+
+General utility functions for foldables
+
+```idris hide
+namespace Foldable
+```
+
+### minBy
+
+```idris
+  ||| Get the minimum element of a collection using the provided comparison
+  ||| function and seed value
+  export
+  minBy : Foldable f => (cmp : a -> a -> Ordering) -> (acc : a) -> f a -> a
+  minBy cmp acc x = 
+    foldl 
+      (\acc, e => 
+        case e `cmp` acc of
+          LT => e
+          _ => acc)
+      acc x
+```
+
+```idris
+  ||| Get the maximum element of a collection using the provided comparison
+  ||| function and seed value
+  export
+  maxBy : Foldable f => (cmp : a -> a -> Ordering) -> (acc : a) -> f a -> a
+  maxBy cmp acc x = 
+    foldl 
+      (\acc, e => 
+        case e `cmp` acc of
+          GT => e
+          _ => acc)
+      acc x
+```
+
 ## Functions
 
 ### repeatN
@@ -138,13 +176,28 @@ Lazily generate all the permutations of a Vect
         (y, z :: ys) :: map (consSnd y) (select (z :: ys))
 ```
 
+### minBy and maxBy
+
+```idris
+  ||| Get the minimum element of a non-empty vector by using the provided
+  ||| comparison function 
+  export
+  minBy : (f : a -> a -> Ordering) -> Vect (S n) a -> a
+  minBy f (x :: xs) = Foldable.minBy f x xs
+
+  ||| Get the maximum element of a non-empty vector by using the provided
+  ||| comparison function 
+  export
+  maxBy : (f : a -> a -> Ordering) -> Vect (S n) a -> a
+  maxBy f (x :: xs) = Foldable.maxBy f x xs
+```
+
 ## Fin
 
 ```idris hide
 namespace Fin
 ```
 
-
 ```idris
   ||| Decriment a Fin, wrapping on overflow
   export