vault backup: 2023-09-07 21:25:19

Algo/Séminaire/Chapter 3 - Case analysis.md

@@ -95,7 +95,37 @@ val f : int -> int = <fun>
 ```Ocaml
 # let and_ a b =
 	match a with 
-		true -> match b with 
+		true -> (match b with 
 			true -> true
-			| false -> false
-		| false -> false;;
+			| false -> false)
+		| false -> false;;
+```
+
+> ⚠️ If you forgot the parentheses, Caml will belived the two `|false` belong to the same pattern matching
+
+### Universal pattern 
+```Ocaml
+# let f x = match x with 
+	0 -> 18
+	| 1 -> 24
+	| _ -> x*x ;;
+```
+
+### "Or" filter
+```Ocaml
+let f x match x with 
+	0 | 20 -> 18
+	| 1 | 11 | 12 -> 24
+	|_ -> x * x ;;
+```
+
+### Guarded filters
+```Ocaml
+let sign x = match x with 
+	0 -> 0
+	| y when y < 0 -> -1
+	| _ -> 1 
+```
+
+> `y when y<0` is an evaluation 
+