X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=blobdiff_plain;f=zipper-lists-continuations.mdwn;h=6ec4d3418ac767f32b687d85c382db31d97f579f;hp=fef92b735ab4224691dfa13c69b6151bde0f9fbb;hb=d522d89b44b4ea898f8089ea2d2c7ec8384770de;hpb=c300cc82d80c40f41a279711fc9c00b06137df60 diff --git a/zipper-lists-continuations.mdwn b/zipper-lists-continuations.mdwn index fef92b73..6ec4d341 100644 --- a/zipper-lists-continuations.mdwn +++ b/zipper-lists-continuations.mdwn @@ -26,10 +26,10 @@ constructor is then we can deduce the unit and the bind: - runit x:'a -> 'a reader = fun (e:env) -> x + r_unit x:'a -> 'a reader = fun (e:env) -> x Since the type of an `'a reader` is `fun e:env -> 'a` (by definition), -the type of the `runit` function is `'a -> e:env -> 'a`, which is a +the type of the `r_unit` function is `'a -> e:env -> 'a`, which is a specific case of the type of the *K* combinator. So it makes sense that *K* is the unit for the reader monad. @@ -43,7 +43,8 @@ We can deduce the correct `bind` function as follows: We have to open up the `u` box and get out the `'a` object in order to feed it to `f`. Since `u` is a function from environments to -objects of type `'a`, we'll have +objects of type `'a`, the way we open a box in this monad is +by applying it to an environment: .... f (u e) ... @@ -228,10 +229,12 @@ Sigh. Ocaml won't show us our own list. So we have to choose an `f` and a `z` that will turn our hand-crafted lists into standard Ocaml lists, so that they will print out. +
 # let cons h t = h :: t;;  (* Ocaml is stupid about :: *)
 # l'_bind (fun f z -> f 1 (f 2 z)) 
           (fun i -> fun f z -> f i (f (i+1) z)) cons [];;
 - : int list = [1; 2; 2; 3]
+
Ta da! @@ -302,3 +305,6 @@ versa. The connections will be expecially relevant when we consider indefinites and Hamblin semantics on the linguistic side, and non-determinism on the list monad side. +Refunctionalizing zippers +------------------------- +