Leonidas-from-XIV · January 18, 2022 16:23 · Jan 18, 2022 · Jan 18, 2022
diff --git a/short_circuit.ml b/short_circuit.ml
@@ -4,6 +4,10 @@ let bigger_than x v = match v > x with true -> Some (v - 1) | false -> None
 (* Sample inputs *)
 let xs = [ 0; 1; 2; 3; 4; 5; 6; 7; 8; 9 ]
 
+(* Why `fold` here in the first place? Maybe your data structure doesn't have `filter_map` etc.
+ * This is an example
+ *)
+
 (* the classic way is to match and evaluate to `acc` on every branch, nesting deeper and deeper *)
 let classic xs =
   List.fold_left

diff --git a/short_circuit.ml b/short_circuit.ml
@@ -0,0 +1,29 @@
+(* Some kind of function that needs to be [Some _] for the rest of the body *)
+let bigger_than x v = match v > x with true -> Some (v - 1) | false -> None
+
+(* Sample inputs *)
+let xs = [ 0; 1; 2; 3; 4; 5; 6; 7; 8; 9 ]
+
+(* the classic way is to match and evaluate to `acc` on every branch, nesting deeper and deeper *)
+let classic xs =
+  List.fold_left
+    (fun acc x ->
+      match bigger_than 3 x with
+      | None -> acc
+      | Some condition1 -> (
+          match bigger_than condition1 x with
+          | None -> acc
+          | Some condition2 -> condition2 :: acc))
+    [] xs
+
+let new_style xs =
+  List.fold_left
+    (fun acc x ->
+      (* instead, we define a custom operator that returns `acc` in the `None` case *)
+      let ( let* ) a f = match a with Some a -> f a | None -> acc in
+      let* condition1 = bigger_than 3 x in
+      let* condition2 = bigger_than condition1 x in
+      condition2 :: acc)
+    [] xs
+
+(* of course the same is possible with operators like `>>=` but it is slightly more messy *)
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