Add lazy list methods to util

src/Util.md

@@ -9,6 +9,7 @@ module Util
 import Data.SortedSet
 import Data.String
 import Data.List.Lazy
+import Data.List1
 
 %default total
 ```
@@ -180,3 +181,32 @@ cartProd x y =
     combine x [] rest = rest
     combine x (y :: ys) rest = (x, y) :: combine x ys rest
 ```
+
+### Concat
+
+Lazily concatenate a LazyList of LazyLists
+
+```idris
+export
+lazyConcat : LazyList (LazyList a) -> LazyList a
+lazyConcat [] = []
+lazyConcat (x :: xs) = x ++ lazyConcat xs
+```
+
+### Group
+
+Lazily group a LazyList
+
+```idris
+export
+lazyGroup : Eq a => LazyList a -> LazyList (List1 a)
+lazyGroup [] = []
+lazyGroup (x :: xs) = lazyGroup' xs x (x ::: [])
+  where
+    lazyGroup' : LazyList a -> (current : a) -> (acc : List1 a) -> LazyList (List1 a)
+    lazyGroup' [] current acc = [acc]
+    lazyGroup' (y :: ys) current acc@(head ::: tail) = 
+      if y == current
+        then lazyGroup' ys current (head ::: (y :: tail))
+        else acc :: lazyGroup (y :: ys)
+```