Konrad, Check out some of the functional data structures found here:
http://www.ccs.neu.edu/racket/pubs/sfp10-kth.pdf VLists may be of particular interest in your case. On Wed, Sep 4, 2013 at 2:37 PM, <users-requ...@racket-lang.org> wrote: > Send users mailing list submissions to > users@racket-lang.org > > To subscribe or unsubscribe via the World Wide Web, visit > http://lists.racket-lang.org/users/listinfo > or, via email, send a message with subject or body 'help' to > users-requ...@racket-lang.org > > You can reach the person managing the list at > users-ow...@racket-lang.org > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of users digest..." > > > [Racket Users list: > http://lists.racket-lang.org/users ] > > > 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 <neil.toro...@gmail.com> > To: users@racket-lang.org > Subject: Re: [racket] Immutable vectors > Message-ID: <52279e7b.5050...@gmail.com> > 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 <neil.toro...@gmail.com> > To: users@racket-lang.org > Subject: [racket] Macro design question: best way to interpret an > expression multiple ways > Message-ID: <5227a6ab.4080...@gmail.com> > 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 <daniel.a.pra...@gmail.com> > To: Matthias Felleisen <matth...@ccs.neu.edu> > Cc: users@racket-lang.org > Subject: Re: [racket] Introductory talk on Contracts and Functional > Contracts, with most examples in Racket > Message-ID: > <CAFKxZVVrzzaw87QhkxAN9WjS22hoTV06-dhsg= > gse+z_dv0...@mail.gmail.com> > Content-Type: text/plain; charset="iso-8859-7" > > On Wed, Sep 4, 2013 at 7:58 AM, Matthias Felleisen <matth...@ccs.neu.edu> > 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: < > http://lists.racket-lang.org/users/archive/attachments/20130905/37e9e432/attachment-0001.html > > > > ------------------------------ > > Message: 4 > Date: Wed, 4 Sep 2013 16:37:09 -0500 > From: Robby Findler <ro...@eecs.northwestern.edu> > To: Daniel Prager <daniel.a.pra...@gmail.com> > Cc: Racket Users <users@racket-lang.org>, Matthias Felleisen > <matth...@ccs.neu.edu> > Subject: Re: [racket] Introductory talk on Contracts and Functional > Contracts, with most examples in Racket > Message-ID: > < > cal3tdometdn4xxymcpxac5rxj6om0m_14-qn-+tspod_unu...@mail.gmail.com> > 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 <daniel.a.pra...@gmail.com > >wrote: > > > On Wed, Sep 4, 2013 at 7:58 AM, Matthias Felleisen <matth...@ccs.neu.edu > > > > 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: > > http://lists.racket-lang.org/users > > > > > -------------- next part -------------- > An HTML attachment was scrubbed... > URL: < > http://lists.racket-lang.org/users/archive/attachments/20130904/630811d2/attachment.html > > > > End of users Digest, Vol 97, Issue 12 > ************************************* > -- Talk to you soon, Scott Klarenbach PointyHat Software Corp. www.pointyhat.ca p 604-568-4280 e sc...@pointyhat.ca 200-1575 W. Georgia Vancouver, BC V6G2V3 _______________________________________ To iterate is human; to recur, divine
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