presentation snippets

presentation/snippets.ml

@@ -0,0 +1,62 @@
+(* easy example *)
+
+
+let numbers = [42; 1337; 2112; 90125; 5040; 7; 1984];;
+
+let rec cata op base l = 
+  match l with
+  | [] -> base
+  | x :: xs -> op x (cata op base xs);;
+
+cata (+) 0 numbers;;
+
+(* or simply *)
+
+List.fold_left (+) 0 numbers;;
+
+(* medium example *)
+
+
+List.fold_left (fun x y -> (x + y) mod 360) 0 numbers;;
+
+
+(*
+  also, you see this with boolean values,
+  in other languages you may use the ternary operator
+  while in ocaml you may use if ... then ... 
+
+  this is also catamorphic because it reduces the 
+  true/false case down to a single value 
+*)
+
+
+let cata_bool case true_case false_case =
+    if case then true_case else false_case;;
+
+let is_raining = true;;
+
+Printf.printf "%s\n" @@ cata_bool is_raining "Use Umbrella" "Wear nice shoes";; 
+
+(* tree example - hardish *)
+
+type int_tree =
+  | Leaf
+  | Node of int * int_tree * int_tree;;
+
+let rec tree_cata leaf_case op tree =
+  match tree with
+  | Leaf -> leaf_case
+  | Node (x, left, right) ->
+    op x
+      (tree_cata leaf_case node_case left)
+      (tree_cata leaf_case node_case right);;
+
+let sum_tree tree =
+  tree_cata 0 (fun x l r -> x + l + r) tree;;
+
+let size_tree tree =
+  tree_cata 0 (fun _ l r -> 1 + l + r) tree;;
+
+let height_tree tree =
+  tree_cata 0 (fun _ l r -> 1 + max l r) tree;;
+