gmane.lisp.scheme.plt

Re: [racket] hack: implicit function arguments

Shriram Krishnamurthi — 2010-08-14T16:07:31

Re: [racket] hack: implicit function arguments

Matthias Felleisen — 2010-08-14T15:54:51

On Aug 14, 2010, at 1:01 AM, Jon Rafkind wrote:


This just lowered my opinion of Scala a lot. I hacked enough TeX (including quasi-higher order) in the 80s to know that parameters shouldn't be numbered, neither explicitly nor implicitly :-)

Re: [racket] hack: implicit function arguments

Jay McCarthy — 2010-08-14T15:20:25

This is very similar to supercut:

http://github.com/jeapostrophe/exp/blob/master/scut.ss

scut allows you to put any expression inside it and it will turn it
into a function. The arguments come from use of _. If you have _i then
it will be the ith argument. If you have _string then the function
will take a "string" keyword argument. The function takes as many
arguments as the maximum i you use inside it. Finally, _... gives you
the rest arg. The bottom of that file has many examples, here are a
few:

((scut _0) 1) => 1

 ((scut (+ _0 (/ _1 _2)))
  1 2 3)
 => (+ 1 (/ 2 3))

((scut (+ _lhs _lhs _rhs)) #:lhs 1 #:rhs 2)
 => 4

 ((scut (apply + _0 _...))
  1 2 3)
 => 6

On Fri, Aug 13, 2010 at 11:01 PM, Jon Rafkind <rafkind< at >cs.utah.edu> wrote:

Re: [racket] Possible to install both plt-scheme from repo and racket from racket-lang.org?

Robby Findler — 2010-08-14T12:10:06

It doesn't do that.

But the racket installation can install in its own directory and then
you just have to delete that directory to uninstall it (under linux).

Robby

On Sat, Aug 14, 2010 at 5:36 AM, Horace Dynamite
<horace.dynamite< at >gmail.com> wrote:
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Re: [racket] Possible to install both plt-scheme from repo and racket from racket-lang.org?

Horace Dynamite — 2010-08-14T10:36:59

I do see a Ubuntu download on the Racket download page,
http://racket-lang.org/download/.
It's a shell script, but since they say it's for Ubuntu, chances are
high that it'll build itself using the debian packing tools and
install itself into the dpkg database so you can remove it with
apt-get/aptitude whatever it is you use.

I can't download 42 MB atm to check, so someone else will have to
confirm how this builds. (careful about possibly "masking" existing
binarys, as I mentioned before).

I think these shell script installers ask you where you'd like to
install the files, called a ``prefix" in case you were wondering
before. I'd chose /opt. So that all the binarys/man pages/etc will be
under /opt/racket. If you decide you'd like to remove Racket, just
remove the /opt/racket directory. You could then add /opt/racket/bin
to the end of your $PATH so that drscheme will still be found in the
cannoncial /usr/... location.

If none of this sounds feasible to you, another option is to ask the
package maintainer

Re: [racket] problems with struct datatype

Guppoc Soft — 2010-08-14T06:11:41

Re: [racket] problems with struct datatype

Noel Welsh — 2010-08-14T06:06:06

You're using #lang scheme instead of #lang racket, I expect.

N.

On Sat, Aug 14, 2010 at 6:37 AM, Guppoc Soft <guppoc-Re5JQEeQqe8AvxtiuMwx3w< at >public.gmane.org> wrote:

[racket] problems with struct datatype

Guppoc Soft — 2010-08-14T05:37:28

[racket] hack: implicit function arguments

Jon Rafkind — 2010-08-14T05:01:41

  I came up with this little hack that lets you avoid giving an explicit 
argument list to functions. Arguments are discovered by usages of 
underscores followed by a number, like _1 and _2. Partly inspired by 
scala; sure to make your blood boil if you love hygiene.

;;; usage
(define/implicit foo1 (printf "~a ~a ~a\n" _8 _9 _8))
(foo1 5 12)

;;; code
#lang racket/base

(require (for-syntax racket/base
                      racket/list
                      syntax/parse
                      )
          racket/stxparam)

(define-syntax-rule (implicits all thing ...)
   (begin
     (define-syntax-parameter thing (lambda (stx)
                                   (raise-syntax-error #f (format "~a 
can only be used in a
  define/implicit function" 'thing))))
     ...
     (provide thing ...)
     (define-for-syntax all (list #'thing ...))))

(implicits all-implicits _1 _2 _3 _4 _5 _6 _7 _8 _9 _10)

(provide define/implicit lambda/implicit)
(define-syntax (lambda/implicit stx)
   (define (find-implicits stx)

Re: [racket] Possible to install both plt-scheme from repo and racket from racket-lang.org?

Byron Gibson — 2010-08-14T04:21:49

Thanks Horace, your first guess was correct, by 'repo' I mean my linux
distro (Ubuntu) software repository.

Thanks for your answer, I suspected that one install would 'clobber'
the other, just wanted to verify.

I prefer to use the distro repository to install software when
possible, since that makes it easier to manage and update (at least
for a relative Linux newbie), but Debian/Ubuntu hasn't updated the
plt-scheme package and dependencies to Racket yet.

Will probably continue using plt-scheme until I come across some
problem I specifically need to update to Racket for.

Thanks!

On Fri, Aug 13, 2010 at 1:13 PM, Horace Dynamite
<horace.dynamite-Re5JQEeQqe8AvxtiuMwx3w< at >public.gmane.org> wrote:

Re: [racket] Macros as a first class objects?

Thomas Chust — 2010-08-14T01:57:59

2010/8/13 Sam Tobin-Hochstadt <samth-1vnkWVZi4QaVc3sceRu5cw< at >public.gmane.org>:

Hello,

syntax-local-value comes close to what I had in mind, but it only
works in the dynamic context of a running transformer procedure. While
this is probably fine for all practical purposes, I'm somewhat
surprised that it is apparently impossible to simply extract the
syntax binding of an identifier given a module or a namespace.

Ciao,
Thomas

Re: [racket] Macros as a first class objects?

Shriram Krishnamurthi — 2010-08-14T01:25:02

No, it's not.  It's the s-expression level that is almost free of
syntax.  At the level of parsing, there's quite a bit of syntax.


I think it's fairly safe to say that, at SOME point in his career,
such an example just may possibly have stolen across Matthias's mind
(-:.  You might learn more by thinking about why it is he rejected
this option, than by trying to sell him on it.

Shriram

Re: [racket] Possible to install both plt-scheme from repo and racket from racket-lang.org?

Horace Dynamite — 2010-08-13T23:13:00

I'm sorry if I have missed something obvious, but I'm not at all sure
what you mean by "repo". First guess is a GNU/Linux distributions
repo, in which case, it's likely that installing one first (say
plt-scheme) and then following that by installing racket (and vice
versa) will clobber some exuctables because Racket installs backward
compatible drscheme (and friends) executables which really run the
drracket (and friends) executables. You could very well get all sorts
of other bizzare behaviour trying this. Smarter package managers might
not even allow such a situation.

You could mean the source code repos from the plt-scheme & racket-lang
sites respectively. In which case, you can pass the
--prefix=/dir/of/your/choice to the configure script when you build
them, and then add aliases in your shell for drscheme and drracket so
that they fire up what you want.

Or you could mean something entirely different. My appologies if I've
misundestood you.

I wonder why you'd want to do this though?

Horace.

Re: [racket] question about foldl implementation

Will Kurt — 2010-08-13T23:27:23

Re: [racket] question about foldl implementation

Will M. Farr — 2010-08-13T22:21:24

+1 from me, too.  I always have to check myself to remember that the foldl accumulator argument comes in on the *right*.  FWIW, OCaml also does it the Haskell way (foldl accumulator on the left, foldr accumulator on the right).  

This also makes the obvious many-argument version more efficient:

(define (foldl kons knil . lists)
  (if (ormap null? lists)
    knil
    (apply foldl kons (apply kons knil (map car lists)) (map cdr lists))))

as opposed to

(define (foldl* kons knil . lists)
  (if (ormap null? lists)
    knil
    (apply foldl* kons (apply kons (append (map car lists) (list knil))) (map cdr lists))))

The extra append is kinda annoying in the foldl* version....

Will

On Aug 13, 2010, at 4:18 PM, Matthias Felleisen wrote:

Re: [racket] Macros: "define" a variable with a transformed id

Jon Rafkind — 2010-08-13T22:08:53

The short answer is hygiene is preventing you from binding identifiers 
created in the macro to escape the scope of the macro. You need to 
unhygienically introduce the identifier you want either through 
syntax-local-introduce or pass the original lexical context (from the 
macro use) to datum->syntax.

Also you it looks like you are trying to munge the names of identifiers 
in the second pattern of `define-filter-category', but you need those 
functions to run at transformation time. Code won't run in a 
syntax-rules, it just gets expanded and returned.

[racket] Macros: "define" a variable with a transformed id

Christopher Bowron — 2010-08-13T21:46:26

I'm trying to write a macro that takes in an id, and creates a
variable with a name based on id, and adds a string based on id into a
list.

If I have (define-filter-category foo), I want it to add
"CICategoryFoo" to the FILTER-CATEGORIES list as well as introduce a
binding for the variable filter-category-foo.  I have the part that
adds the string to the list, but I do not know how to manipulate the
id and introduce the variable.  Can anyone shed some light on this for
me?  Thanks

What I have so far:

(define FILTER-CATEGORIES empty)

(define (id->category-string n)
  (define (camel-case str)
    (regexp-replace* #rx"-" (string-titlecase str) ""))
  (string-append "CICategory" (camel-case (symbol->string n))))

(define (id->category-id n)
  (string->symbol (string-append "filter-category-" (symbol->string n))))

(define-syntax define-filter-category
  (syntax-rules ()
    ((_ id string)
     (begin
       ;;; FIXME: also (define ,id  string)
       (set! FILTER-CATEGORIES (cons string FILTER-CATEGORIES))))

[racket] Possible to install both plt-scheme from repo and racketfrom racket-lang.org?

Byron Gibson — 2010-08-13T21:40:52

Is it possible to install both of these, or do they overwrite parts of
each other?

Re: [racket] question about foldl implementation

Jos Koot — 2010-08-13T21:26:52

+1,
jos

Re: [racket] question about foldl implementation

Matthias Felleisen — 2010-08-13T21:18:54

I privately +1ed Joe, and I all supportive of introducing new folds and phasing out the old ones. 


On Aug 13, 2010, at 4:04 PM, Sam Tobin-Hochstadt wrote:

Re: [racket] question about foldl implementation

Sam Tobin-Hochstadt — 2010-08-13T20:04:48

The Haskell ordering also has the advantage of fitting with the Typed
Racket type system for variable-arity functions.