<div dir="ltr"><div style="font-family:arial,sans-serif;font-size:13px">Konrad,</div><div style="font-family:arial,sans-serif;font-size:13px"> </div><div style="font-family:arial,sans-serif;font-size:13px">Check out some of the functional data structures found here:</div> <div style="font-family:arial,sans-serif;font-size:13px"> </div><a href="http://www.ccs.neu.edu/racket/pubs/sfp10-kth.pdf" target="_blank" style="font-family:arial,sans-serif;font-size:13px">http://www.ccs.neu.edu/racket/pubs/sfp10-kth.pdf</a> <div style="font-family:arial,sans-serif;font-size:13px"> </div><div style="font-family:arial,sans-serif;font-size:13px">VLists may be of particular interest in your case.</div><div class="gmail_extra"> <div class="gmail_quote"> On Wed, Sep 4, 2013 at 2:37 PM, <<a href="mailto:users-request@racket-lang.org" target="_blank">users-request@racket-lang.org</a>> wrote: <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"> Send users mailing list submissions to <a href="mailto:users@racket-lang.org">users@racket-lang.org</a> To subscribe or unsubscribe via the World Wide Web, visit <a href="http://lists.racket-lang.org/users/listinfo" target="_blank">http://lists.racket-lang.org/users/listinfo</a> or, via email, send a message with subject or body 'help' to <a href="mailto:users-request@racket-lang.org">users-request@racket-lang.org</a> You can reach the person managing the list at <a href="mailto:users-owner@racket-lang.org">users-owner@racket-lang.org</a> When replying, please edit your Subject line so it is more specific than "Re: Contents of users digest..." [Racket Users list: <a href="http://lists.racket-lang.org/users" target="_blank">http://lists.racket-lang.org/users</a> ] Today's Topics: 1. Re: Immutable vectors (Neil Toronto) 2. Macro design question: best way to interpret an expression multiple ways (Neil Toronto) 3. Re: Introductory talk on Contracts and Functional Contracts, with most examples in Racket (Daniel Prager) 4. Re: Introductory talk on Contracts and Functional Contracts, with most examples in Racket (Robby Findler) ---------------------------------------------------------------------- Message: 1 Date: Wed, 04 Sep 2013 14:56:27 -0600 From: Neil Toronto <<a href="mailto:neil.toronto@gmail.com">neil.toronto@gmail.com</a>> To: <a href="mailto:users@racket-lang.org">users@racket-lang.org</a> Subject: Re: [racket] Immutable vectors Message-ID: <<a href="mailto:52279E7B.5050406@gmail.com">52279E7B.5050406@gmail.com</a>> Content-Type: text/plain; charset=UTF-8; format=flowed On 09/04/2013 10:28 AM, Konrad Hinsen wrote: > For the kind of data I am working with, immutable vectors look like > just the right choice: immutable and O(1) element access. However, I > am discovering that they are a real pain to work with. > > Pretty much any vector operation returns a mutable vector: vector-map, > vector-drop, vector-split-at, etc. I have to use > vector->immutable-vector afterwards to get what I want. That's a lot > of code clutter, and a lot of unnecessary object generation. > Getting data from a stream into an immutable vector is the worst: it > requires two intermediates: sequence->list, list->vector, > vector->immutable-vector. > > So I am beginning to wonder if immutable vectors are some obsolete > feature that is being discouraged. Is there a better choice for an > immutable sequence with O(1) element access? Racket's language design philosophy encourages immutability, so I don't see them going away any time soon. Immutable vectors is one area the standard library doesn't (currently) meet its design goals, IMO. FWIW, `vector->immutable-vector' is pretty fast. It's usually the least significant part of an O(n) operation. Its two biggest problems are that it allocates memory and annoys people. If you're working in Typed Racket, you might consider using the `math/array' library. It provides multidimensional arrays with O(1) access, a lot of ways to slice and dice them, and less memory allocation (especially if you use nonstrict arrays). They're not necessarily faster than vectors, though. Strict immutable arrays are backed by a mutable vector, so they allow element access only via a getter, which introduces an extra function call. If you're not in Typed Racket, don't use `math/array' because the contract barrier makes element access very slow. But you might be able to do something similar: have library functions operate on mutable vectors, with user-facing functions accepting and receiving immutable vectors, or some more abstract wrapper data type. The `math/matrix' library does this, and it works out well enough. A lot of matrix operations are fastest when done in-place (e.g. Gaussian elimination), but *composing* matrix operations is easiest to reason about when matrices are immutable. Many matrix functions copy their arguments' elements to a vector, operate destructively on it, and return the result wrapped in an array. Neil ? ------------------------------ Message: 2 Date: Wed, 04 Sep 2013 15:31:23 -0600 From: Neil Toronto <<a href="mailto:neil.toronto@gmail.com">neil.toronto@gmail.com</a>> To: <a href="mailto:users@racket-lang.org">users@racket-lang.org</a> Subject: [racket] Macro design question: best way to interpret an expression multiple ways Message-ID: <<a href="mailto:5227A6AB.4080502@gmail.com">5227A6AB.4080502@gmail.com</a>> Content-Type: text/plain; charset=UTF-8; format=flowed I have two libraries of combinators meant to be used as targets for a language semantics. I'm implementing the semantics using macros; e.g. #'(interp (+ 4 5)) => #'(((const 4) . &&& . (const 5)) . >>> . add) where `interp' is a macro and `=>' means macro expansion. Here's the tricky part. I have to interpret the language using *both* combinator libraries, not just one; e.g. I need #'(interp (+ 4 5)) to expand to both of these: #'(((const/bot 4) . &&&/bot . (const/bot 5)) . >>>/bot . add/bot) #'(((const/pre 4) . &&&/pre . (const/pre 5)) . >>>/pre . add/pre) I could have #'(interp (+ 4 5)) expand to something like #'(list (interp/bot (+ 4 5)) (interp/pre (+ 4 5))) But expanding twice is terrible manners when the expression contains macros. (Originally, I had super-combinators that did the job of both */bot and */pre combinators. These super-combinators were complicated and messy, especially when used in recursion, which is why I'm moving the "interpret the language two ways" job into the macro system and hoping it's nicer. It should also generate faster code, and possibly allow type checking on one of the interpretations.) The best idea I've had so far is to have (interp e) expand to uses of generic `&&&' and `>>>' combinators, apply `local-expand', and do a syntax tree search-and-replace that does #'&&& => #'&&&/bot, etc. Is there another way, though, that doesn't run afoul of macro security? Neil ? ------------------------------ Message: 3 Date: Thu, 5 Sep 2013 07:33:10 +1000 From: Daniel Prager <<a href="mailto:daniel.a.prager@gmail.com">daniel.a.prager@gmail.com</a>> To: Matthias Felleisen <<a href="mailto:matthias@ccs.neu.edu">matthias@ccs.neu.edu</a>> Cc: <a href="mailto:users@racket-lang.org">users@racket-lang.org</a> Subject: Re: [racket] Introductory talk on Contracts and Functional Contracts, with most examples in Racket Message-ID: <CAFKxZVVrzzaw87QhkxAN9WjS22hoTV06-dhsg=<a href="mailto:GSe%2BZ_dV0zmA@mail.gmail.com">GSe+Z_dV0zmA@mail.gmail.com</a>> Content-Type: text/plain; charset="iso-8859-7" On Wed, Sep 4, 2013 at 7:58 AM, Matthias Felleisen <<a href="mailto:matthias@ccs.neu.edu">matthias@ccs.neu.edu</a>> wrote: You can't. Sam has had this combination on his todo list for 7 years and > he never got around to it. Perhaps I signed his dissertation too early :-) I noticed that contract support is missing from TR. I have, however, constructed a roll-my-own contract example with TR, and it would be great if Sam (or another!) pushed forward on contract support for TR. This is from my code base. It is a function that consumes the dimensions of > a (functional image) canvas and created a gridded image and an event > handler that tells you on which "tile" a user clicked. It is highly real, > higher-order, dependent, and yet not difficult to understand. Alas, I am having trouble mentally parsing this, but may still flash it up (with acknowledgement!) as a realistic example. In trying to construct a simpler (yet not easily do-able with static types) example I'm running into trouble getting my subcontract right. I get an "n unbound identifier" error on the penultimate line: ;; make-indenter: Nat -> (String -> String) ;; ;; Example: ((make-indenter 4) "foo") -> " foo" ;; (define/contract (make-indenter n) (->i ([n natural-number/c]) [r (->i ([s string?]) [result string?] #:post (s result) (= (string-length result) (+ n (string-length s))))]) (? (s) (string-append (make-string n #\space) s))) How should I access 'n'? Many thanks Dan -------------- next part -------------- An HTML attachment was scrubbed... URL: <<a href="http://lists.racket-lang.org/users/archive/attachments/20130905/37e9e432/attachment-0001.html" target="_blank">http://lists.racket-lang.org/users/archive/attachments/20130905/37e9e432/attachment-0001.html</a>> ------------------------------ Message: 4 Date: Wed, 4 Sep 2013 16:37:09 -0500 From: Robby Findler <<a href="mailto:robby@eecs.northwestern.edu">robby@eecs.northwestern.edu</a>> To: Daniel Prager <<a href="mailto:daniel.a.prager@gmail.com">daniel.a.prager@gmail.com</a>> Cc: Racket Users <<a href="mailto:users@racket-lang.org">users@racket-lang.org</a>>, Matthias Felleisen <<a href="mailto:matthias@ccs.neu.edu">matthias@ccs.neu.edu</a>> Subject: Re: [racket] Introductory talk on Contracts and Functional Contracts, with most examples in Racket Message-ID: <<a href="mailto:CAL3TdOMETDN4xxymcpxaC5RxJ6oM0M_14-QN-%2BtSpOD_uNuZzQ@mail.gmail.com">CAL3TdOMETDN4xxymcpxaC5RxJ6oM0M_14-QN-+tSpOD_uNuZzQ@mail.gmail.com</a>> Content-Type: text/plain; charset="utf-8" You need to indicate that the contract on 'r' needs 'n', ie replace "[r (->i" with "[r (n) (->i". Robby On Wed, Sep 4, 2013 at 4:33 PM, Daniel Prager <<a href="mailto:daniel.a.prager@gmail.com">daniel.a.prager@gmail.com</a>>wrote: > On Wed, Sep 4, 2013 at 7:58 AM, Matthias Felleisen <<a href="mailto:matthias@ccs.neu.edu">matthias@ccs.neu.edu</a>> > wrote: > > You can't. Sam has had this combination on his todo list for 7 years and >> he never got around to it. Perhaps I signed his dissertation too early :-) > > > I noticed that contract support is missing from TR. I have, however, > constructed a roll-my-own contract example with TR, and it would be great > if Sam (or another!) pushed forward on contract support for TR. > > This is from my code base. It is a function that consumes the dimensions >> of a (functional image) canvas and created a gridded image and an event >> handler that tells you on which "tile" a user clicked. It is highly real, >> higher-order, dependent, and yet not difficult to understand. > > > Alas, I am having trouble mentally parsing this, but may still flash it up > (with acknowledgement!) as a realistic example. > > In trying to construct a simpler (yet not easily do-able with static > types) example I'm running into trouble getting my subcontract right. > > I get an "n unbound identifier" error on the penultimate line: > > ;; make-indenter: Nat -> (String -> String) > ;; > ;; Example: ((make-indenter 4) "foo") -> " foo" > ;; > (define/contract (make-indenter n) > (->i ([n natural-number/c]) > [r (->i ([s string?]) > [result string?] > #:post (s result) (= (string-length result) > (+ n (string-length s))))]) > (? (s) (string-append (make-string n #\space) s))) > > > How should I access 'n'? > > > Many thanks > > Dan > > ____________________ > Racket Users list: > <a href="http://lists.racket-lang.org/users" target="_blank">http://lists.racket-lang.org/users</a> > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <<a href="http://lists.racket-lang.org/users/archive/attachments/20130904/630811d2/attachment.html" target="_blank">http://lists.racket-lang.org/users/archive/attachments/20130904/630811d2/attachment.html</a>> End of users Digest, Vol 97, Issue 12 ************************************* </blockquote></div> <div> </div>-- Talk to you soon, Scott Klarenbach PointyHat Software Corp. <a href="http://www.pointyhat.ca" target="_blank">www.pointyhat.ca</a> p 604-568-4280 e <a href="mailto:scott@pointyhat.ca" target="_blank">scott@pointyhat.ca</a> 200-1575 W. Georgia Vancouver, BC V6G2V3 _______________________________________ To iterate is human; to recur, divine </div></div>