Re: Guile 2 birthday potluck
Hi! Limbo Peng skribis: > BTW: did you guys have a hack-potluck last year? Yes, just not under this name. ;-) Check http://www.gnu.org/software/guile/news.html under 2012-02-16. Happy hacking! Ludo’.
call-with-values and primitives
Hello. Why does it return -1? Could anyone explain? (Comments are mine.) (call-with-values (lambda () (values 4 5)) (lambda (a b) b)) ; a is 4 and b is 5; return 5 ⇒ 5 (call-with-values * -) ⇒ -1 More: (call-with-values + +) 0 (call-with-values + -) 0 (call-with-values - -) ERROR: Wrong number of arguments to - ABORT: (wrong-number-of-args) https://gnu.org/software/guile/manual/guile.html#Multiple-Values
Re: http-post
On Tue 17 Apr 2012 05:34, gregory benison writes: > "More helper procedures for the other common HTTP verbs would be a > good addition to this module. Send your code to ." > > So, I say to guile-user, "here is my code". Thanks! I used it as a base for a patch I just pushed. Guile now has client wrappers for all HTTP verbs except CONNECT. Appending the documentation. A websocket implementation would be nice. > I think the next steps after this patch are to: > - be able to work with a greater variety of encodings; > - since form data of the type "key1=value1&key2=value2..." is so > common in POST bodies, accept post data as key-value pairs represented > by an alist (which would be coerced into a bytevector automatically). Yes this would be good. Want to make a patch? Regards, Andy File: guile.info, Node: Web Client, Next: Web Server, Prev: Responses, Up: Web 7.3.8 Web Client `(web client)' provides a simple, synchronous HTTP client, built on the lower-level HTTP, request, and response modules. -- Scheme Procedure: open-socket-for-uri uri Return an open input/output port for a connection to URI. -- Scheme Procedure: http-get uri keyword-arg... -- Scheme Procedure: http-head uri keyword-arg... -- Scheme Procedure: http-post uri keyword-arg... -- Scheme Procedure: http-put uri keyword-arg... -- Scheme Procedure: http-delete uri keyword-arg... -- Scheme Procedure: http-trace uri keyword-arg... -- Scheme Procedure: http-options uri keyword-arg... Connect to the server corresponding to URI and make a request over HTTP, using the appropriate method (`GET', `HEAD', etc.). All of these procedures have the same prototype: a URI followed by an optional sequence of keyword arguments. These keyword arguments allow you to modify the requests in various ways, for example attaching a body to the request, or setting specific headers. The following table lists the keyword arguments and their default values. `#:body #f' `#:port (open-socket-for-uri URI)]' `#:version '(1 . 1)' `#:keep-alive? #f' `#:headers '()' `#:decode-body? #t' `#:streaming? #f' If you already have a port open, pass it as PORT. Otherwise, a connection will be opened to the server corresponding to URI. Any extra headers in the alist HEADERS will be added to the request. If BODY is not #f, a message body will also be sent with the HTTP request. If BODY is a string, it is encoded according to the content-type in HEADERS, defaulting to UTF-8. Otherwise BODY should be a bytevector, or `#f' for no body. Although a message body may be sent with any request, usually only `POST' and `PUT' requests have bodies. If DECODE-BODY? is true, as is the default, the body of the response will be decoded to string, if it is a textual content-type. Otherwise it will be returned as a bytevector. However, if STREAMING? is true, instead of eagerly reading the response body from the server, this function only reads off the headers. The response body will be returned as a port on which the data may be read. Unless KEEP-ALIVE? is true, the port will be closed after the full response body has been read. Returns two values: the response read from the server, and the response body as a string, bytevector, #f value, or as a port (if STREAMING? is true). `http-get' is useful for making one-off requests to web sites. If you are writing a web spider or some other client that needs to handle a number of requests in parallel, it's better to build an event-driven URL fetcher, similar in structure to the web server (*note Web Server::). Another option, good but not as performant, would be to use threads, possibly via par-map or futures. -- http://wingolog.org/
Re: call-with-values and primitives
brom...@lavabit.com writes: > Hello. > > Why does it return -1? Could anyone explain? > (Comments are mine.) The general principle is to try and give sensible results when +,*,etc are called with a number of arguments other than 2. By thinking them through at this level you can, in theory, write more general code and have it "just work". Not only does it apply to various functions, but it is generally considered a sensible macro design principle too, as in the case of, among others, 'and' and 'or'. > > (call-with-values (lambda () (values 4 5)) > (lambda (a b) b)) ; a is 4 and b is 5; return 5 > ⇒ 5 > > (call-with-values * -) > ⇒ -1 If you call * with 0 arguments, it returns one value, the number 1. This makes some sense since 1 is the identity for multiplication. i.e. (* 1 x) = x = (* x 1) for all x If you call - with one argument, it negates that argument, as if you had done (- 0 x). Putting both of these together, (call-with-values * -) is equivalent to (- (*)) scheme@(guile−user)> (*) $2 = 1 scheme@(guile−user)> (- 1) $3 = −1 scheme@(guile−user)> (- (*)) $4 = −1 > (call-with-values + +) > 0 Similarly to multiplication, if you call (+) with one argument, you get the identity for +, which is 0. This expression then, is equivalent to (+ (+)) = (+ 0) = 0 > (call-with-values + -) > 0 Similar to the above situation, you can think of this as being equivalent to (- (+)). Negating 0, naturally enough, gives you 0. scheme@(guile−user)> (+) $5 = 0 scheme@(guile−user)> (- (+)) $6 = 0 > (call-with-values - -) > ERROR: Wrong number of arguments to - While we extend / and - to have sensible results for the one argument case (reciprocal and negation), and we extend it for more than two arguments, there is not an identity for / or - [0], so we mark the zero argument case as errors for both. scheme@(guile−user)> (/) ERROR: In procedure /: ERROR: Wrong number of arguments to / scheme@(guile−user)> (-) ERROR: In procedure −: ERROR: Wrong number of arguments to − [0] Well, more correctly, they have right identities, of 1 and 0 respectively, but no left ones -- Ian Price -- shift-reset.com "Programming is like pinball. The reward for doing it well is the opportunity to do it again" - from "The Wizardy Compiled"
Re: call-with-values and primitives
On Fri 11 Jan 2013 15:23, brom...@lavabit.com writes: > (call-with-values * -) > ⇒ -1 So it's like: (call-with-values producer consumer) The producer is called with no arguments, then the results of that call are passed to the consumer. So first `*' is called with no arguments, like this: (*) Calling `*' always returns just one value, so in this case it's equivalent to binding a single value, so the original expression is completely equivalent to: (let ((tmp (*))) (- tmp)) Reducing this further: => (let ((tmp 1)) (- tmp)) => (- 1) => -1 See the R5RS for more, including the definition of (*) and (+). > (call-with-values + +) > 0 (let ((tmp (+))) (+ tmp)) > (call-with-values + -) > 0 (let ((tmp (+))) (- tmp)) > (call-with-values - -) (let ((tmp (-))) (- tmp)) > ERROR: Wrong number of arguments to - > ABORT: (wrong-number-of-args) (-) has no sensible answer. Happy hacking, Andy -- http://wingolog.org/
Re: Readline support in Cygwin
On Wed, Jan 9, 2013 at 3:57 PM, Ludovic Courtès wrote: > Hi! > > Akop Pogosian skribis: > >> # ERROR: In procedure load-extension: >> # ERROR: In procedure dynamic-link: file: "libguilereadline-v-18", >> message: "The specified module could not be found." > > [...] > >> # $ ls software/packages/guile-2.0.7/lib/ >> # guile libguile-2.0.la libguilereadline-v-18.la >> # libguile-2.0.a libguilereadline-v-18.a pkgconfig > > As you can see, you only have a static version of libguilereadline, > which is why ‘dynamic-link’ fails. Indeed. I am really confused about why there are no shared libraries in /usr/lib under cygwin. However, they are installed in /usr/bin under strange names such as /usr/bin/cygreadline6.dll Is guile build system supposed to pick up shared libraries in those locations or do I need to do something special?
