From: Jim Pryor Date: Fri, 24 Dec 2010 03:29:22 +0000 (-0500) Subject: ass10 hint tweaks X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=commitdiff_plain;h=399197e0af7c4b80f326be60ff2c0caae74b3687;ds=inline ass10 hint tweaks Signed-off-by: Jim Pryor --- diff --git a/hints/assignment_10_hint_2.mdwn b/hints/assignment_10_hint_2.mdwn index 83be68fb..9bb1cd66 100644 --- a/hints/assignment_10_hint_2.mdwn +++ b/hints/assignment_10_hint_2.mdwn @@ -12,11 +12,11 @@ But I found it easier to work out the solution using the simpler "tree\_monadize It makes debugging easier if we work with a tree whose starting leaf -elements are differently types than the tree we aim to finish with. So: +elements are differently typed than the tree we aim to finish with. So: let tree = Node(Leaf '1', Node(Leaf '2', Node(Leaf '3', Leaf '1')));; -Now, we already know how to count the leaves using a continuation monad +Now, we already know how to count the leaves using a Continuation monad in tree shape: let v0 = TreeCont.monadize (fun a k -> 1 + k a) tree (fun t -> 0);; @@ -28,9 +28,9 @@ of each value, rather than how many leaves in total: let update_env e x = fun y -> (if x = y then 1 else 0) + e y;; - let v1 = TreeCont.monadize (fun a k e -> - let e_prev = k a e - in update_env e_prev a + let v1 = TreeCont.monadize (fun a k e0 -> + let ecur = k a e0 + in update_env ecur a ) tree (fun t e -> e) (fun a -> 0);; (* now @@ -39,7 +39,7 @@ of each value, rather than how many leaves in total: v1 '2' ~~> 1 *) -How does this work? Our distributed function (fun a k e -> ...) takes a leaf element a and a continuation k, which maps leaf elements and environments e to new environments. +How does this work? Our distributed function `fun a k e -> ...` takes a leaf element `a` and a continuation `k`, which maps leaf elements and environments `e0` to new environments `ecur`. It gives back a function from `e0` to an updated version of `ecur`. Our seed function here is the initial continuation. Instead of taking a leaf element and an env, it takes a tree of such elements and an env. In general, wherever the distributed function takes `'a`s, the seed function takes `'a tree`s.