X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=blobdiff_plain;f=week7.mdwn;h=3336a49685b38bf087eb3a9f67915f3bf8a32ea0;hp=a78a77e291a6d71883a8acadd5bdc3fa9f2769c4;hb=f10b70d2b7589e44135dd0e47c87d3965ee08918;hpb=ef954bbcb3b568413e2dd48374dbeb7201ccd4bb diff --git a/week7.mdwn b/week7.mdwn index a78a77e2..3336a496 100644 --- a/week7.mdwn +++ b/week7.mdwn @@ -105,26 +105,26 @@ them from hurting the people that use them or themselves. object, we have `(unit x) * f == f x`. For instance, `unit` is a function of type `'a -> 'a option`, so we have -
-    # let ( * ) m f = match m with None -> None | Some n -> f n;;
-    val ( * ) : 'a option -> ('a -> 'b option) -> 'b option = 
-    # let unit x = Some x;;
-    val unit : 'a -> 'a option = 
-    # unit 2 * unit;;
-    - : int option = Some 2
-    
- - The parentheses is the magic for telling Ocaml that the - function to be defined (in this case, the name of the function - is `*`, pronounced "bind") is an infix operator, so we write - `m * f` or `( * ) m f` instead of `* m f`. +
+# let ( * ) m f = match m with None -> None | Some n -> f n;;
+val ( * ) : 'a option -> ('a -> 'b option) -> 'b option = 
+# let unit x = Some x;;
+val unit : 'a -> 'a option = 
+# unit 2 * unit;;
+- : int option = Some 2
+
+ +The parentheses is the magic for telling Ocaml that the +function to be defined (in this case, the name of the function +is `*`, pronounced "bind") is an infix operator, so we write +`m * f` or `( * ) m f` instead of `* m f`. * Associativity: bind obeys a kind of associativity, like this: - (m * f) * g == m * (fun x -> f x * g) + `(m * f) * g == m * (fun x -> f x * g)` - If you don't understand why the lambda form is necessary, you need - to look again at the type of bind. This is important. + If you don't understand why the lambda form is necessary (the "fun + x" part), you need to look again at the type of bind. For an illustration of associativity in the option monad: