X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=blobdiff_plain;f=hints%2Fassignment_7_hint_4.mdwn;h=346d98b30bcd90c4d387d11f0460de7220ab4b49;hp=d41e0f0adff4da5916b6388b89a1eda1f762106b;hb=002bbc4734d89967f6941fcff5021b4d1c661f2b;hpb=458cadab1427b0fc0f7bc8689f1dddb18b2201e7 diff --git a/hints/assignment_7_hint_4.mdwn b/hints/assignment_7_hint_4.mdwn index d41e0f0a..346d98b3 100644 --- a/hints/assignment_7_hint_4.mdwn +++ b/hints/assignment_7_hint_4.mdwn @@ -18,7 +18,7 @@ in (truth_value', r, h)) in bind_set u (fun one_dpm -> unit_set (bind_dpm one_dpm eliminate_non_Qxs)) - The first three seven lines here just perfom the operation we described: return a `bool dpm` computation that only yields `true` whether its input `(r, h)` associates variable `x` with the right sort of entity. The last line performs the `bind_set` operation. This works by taking each `dpm` in the set and returning a `unit_set` of a filtered `dpm`. The definition of `bind_set` takes care of collecting together all of the `unit_set`s that result for each different set element we started with. + The first seven lines here just perfom the operation we described: return a `bool dpm` computation that only yields `true` when its input `(r, h)` associates variable `x` with the right sort of entity. The last line performs the `bind_set` operation. This works by taking each `dpm` in the set and returning a `unit_set` of a filtered `dpm`. The definition of `bind_set` takes care of collecting together all of the `unit_set`s that result for each different set element we started with. We can call the `(fun one_dpm -> ...)` part \[[Qx]] and then updating `u` with \[[Qx]] will be: @@ -54,7 +54,9 @@ then empty_set else unit_set (bind dpm entity_dpm (fun e -> unit_dpm (Q e))) - Doing things this way will discard `bool dpm`s that start out wrapping `false`, and will pass through other `bool dpm`s that start out wrapping `true` but which our current filter transforms to a wrapped `false`. You might instead aim for consistency, and always pass through wrapped `false`s, whether they started out that way or are only now being generated; or instead always discard such, and only pass through wrapped `true`s. But what we have here will work fine too. + Applied to an entity_dpm, that yields a function that we can bind to a `bool dpm set` and that will transform the doubly-wrapped `bool` into a new `bool dpm set`. + + Doing things this way will discard `bool dpm`s from the set that started out wrapping `false`, and will pass through other `bool dpm`s that start out wrapping `true` but which our current filter transforms to a wrapped `false`. You might instead aim for consistency, and always pass through wrapped `false`s, whether they started out that way or are only now being generated; or instead always discard such, and only pass through wrapped `true`s. But what we have here will work fine too. If we let that be \[[Q]], then \[[Q]] \[[x]] would be: