q-lang-users — general discussion, questions, suggestions, etc.

Re: [q-lang-users] ANN: Q 7.3 RC1 and Q Lex+Yacc 0.1 available

[Albert G. <Dr....@t-...>]

John Cowan wrote:
> I did a "make uninstall" from the q-7.2 directory, then removed q-7.3
> and remade it from the untouched tarball.  Same error.

As promised, I checked the native Windows port with the latest cvs and 
it builds and runs fine. I've also reviewed the (very few) changes 
between 7.2 and the latest cvs and I don't see anything in there which 
could possibly break the module loader; in fact a 7.2 libq should still 
work fine since there were no changes in it.

Could you please try and recompile the most recent version that you had 
working on your system (7.2 I guess) and see whether it still builds ok?

Albert

-- 
Dr. Albert Gr"af
Dept. of Music-Informatics, University of Mainz, Germany
Email:  Dr....@t-..., ag...@mu...
WWW:    http://www.musikinformatik.uni-mainz.de/ag

Re: [q-lang-users] Q as a Computer Algebra System

[dx <dx...@ac...>]

Hi,

I am attaching the source code that I found.

dex

Albert Graef wrote:
> dx wrote:
>> By the way, is there anyone knows Wm Leler's Bertrand(augmented term rewriting),
>> I read the book a long time ago, I am just wondering how close it is to Q.
> 
> Sounds interesting. Interesting guy, too. I googled around some but most 
> links to actual information and the sources seem to be dead. Does anyone 
> have the sources for Bertrand lying around somewhere? I'd like to take a 
> look, too.
> 
> Albert
> 

Re: [q-lang-users] Q as a Computer Algebra System

[Albert G. <Dr....@t-...>]

Anthony wrote:
> What I'd like to do is just write a small Q program
> that parses a line of input according to the rules of
> Mathematica.  No need to evaluate the functions...just
> want to build a syntax checker at first.

Concerning the parser for the input language, that should be a nice 
opportunity to try Q Yacc+Lex. (The lexical analyzers generated by Q Lex 
are still a bit slow right now, but I'm working on this.)

But, as Rob already explained, building a CAS, even a basic one, is not 
as simple as it might look.

> Or maybe I am dreaming...

Well, I started dreaming about an easy-to-use FP language one day... :)

Cheers,
Albert

-- 
Dr. Albert Gr"af
Dept. of Music-Informatics, University of Mainz, Germany
Email:  Dr....@t-..., ag...@mu...
WWW:    http://www.musikinformatik.uni-mainz.de/ag

Re: [q-lang-users] Q as a Computer Algebra System

[Albert G. <Dr....@t-...>]

dx wrote:
> By the way, is there anyone knows Wm Leler's Bertrand(augmented term rewriting),
> I read the book a long time ago, I am just wondering how close it is to Q.

Sounds interesting. Interesting guy, too. I googled around some but most 
links to actual information and the sources seem to be dead. Does anyone 
have the sources for Bertrand lying around somewhere? I'd like to take a 
look, too.

Albert

-- 
Dr. Albert Gr"af
Dept. of Music-Informatics, University of Mainz, Germany
Email:  Dr....@t-..., ag...@mu...
WWW:    http://www.musikinformatik.uni-mainz.de/ag

Re: [q-lang-users] Q as a Computer Algebra System

[dx <dx...@ac...>]

Hi,

If you want CAS, you can try Maxima or Axiom.

By the way, is there anyone knows Wm Leler's Bertrand(augmented term rewriting),
I read the book a long time ago, I am just wondering how close it is to Q.

Thanks,
dex

Rob Hubbard wrote:
> Hello Anthony,
> 
> I too first became interested in 'Q' because of mathematics. I am
> fairly new to Q too.
> 
> Q is not, in my view, a typical functional language. If you're
> interested in learning functional languages, you should also take a
> look at some others. It would probably be instructive to try Standard
> ML <http://www.smlnj.org/>. There are many other interesting
> functional languages. However, I think you will really enjoy using Q.
> It's one of the languages that I most enjoy using.
> 
> Beware that Q may not always behave quite as you expect at first. For
> example, if you enter the simple program consisting of just the
> rewrite rule:
>     X+X = 2*X;
> and the giving Q some expressions to reduce:
>     ==> A+A+B
>     2*A+B
>     ==> A+B+B
>     A+B+B
> the final response from Q may not be what you expect.
> 
> A+B+B, which is (A+B)+B due to the left-associativity of (+), was not
> reduced, as this does not match the given rule.
> With the additional rule
>     Y+X+X = Y+2*X;
> you will now get the responses from the Q system
>     ==> A+B+B
>     A+2*B
>     ==> A+A+B+B+C+C+D+D
>     2*A+2*B+2*C+2*D
> 
> To quote Albert Graef's informative reply to one of my questions:
> 'Yes, it's surprisingly hard to do apparently basic stuff like this,
> because it involves "rewriting modulo AC" (AC =
> associativity/commutativity). The conventional way to deal with this
> is to transform the original terms into a "sum of products" normal
> form and represent that as a list which is lexicographically ordered
> according to the involved symbols. It's not really that hard to do but
> it indeed involves additional rules on a kind of meta-level, so there
> is no straightforward solution with just a few equations.'
> 
> I was at first disappointed with Q not being the simple computer
> algebra system I hoped it would be. But then that's not what it's
> intended to be. Once you get used to it, you find that Q does seem to
> do the "right thing". Those involved with developing Q take great care
> to keep Q a sensible and consistent language. (See for example the
> helpful reply from John Cowan in a discussion
> <http://sourceforge.net/mailarchive/message.php?msg_id=19294969> of
> type tests, in the lead up to the release of Q7.2)
> 
> Not many languages that I know are so well thought out, but I think
> that Q is. And Q has fairly comprehensive libraries, together with
> comprehensive programming tools, such as the debugger.
> 
> When I want to do some maths, I now usually reach for Q. But I tend to
> write code for the specific type of mathematical object I'm currently
> interested in. I imagine that to write a fairly comprehensive symbolic
> computer algebra system would be a job of comparable complexity in any
> language, Q, C++, ML, Python, or any other "general purpose" language.
> 
> By the way, if anyone does know of a good free / open source symbolic
> computer algebra system or programming language, please let me know.
> Mathematica is unbelievably expensive, and I don't need anything that
> powerful or comprehensive.
> 
> I hope these comments (and opinions) are helpful,
> Rob.
> 
> On 15/08/06, Anthony <ad...@ke...> wrote:
>> Just a general question...Q is my first experience
>> with a functional language.  What would it take to
>> write a Mathematica clone in Q?
>>
>> I don't mean a full-Mathematica clone, but something
>> that would emulate the kernel mode, circa 1988--an
>> unlimited integer, numeric, graphical, and symbolic
>> program with an easy syntax.
>>
>> For example x + 8  will generate internally a
>> Plus[x,8] production, and 1+x^2+(y+z)^2 generates
>>
>> Plus[1, Power[x,2], Power[Plus[y,z],2]]
>>
>> What I'd like to do is just write a small Q program
>> that parses a line of input according to the rules of
>> Mathematica.  No need to evaluate the functions...just
>> want to build a syntax checker at first.
>>
>> Or maybe I am dreaming...
> 
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Re: [q-lang-users] Q as a Computer Algebra System

[Kristof B. <kr...@vl...>]

"Rob Hubbard" <hub...@gm...> writes:
> <snip>
>
> By the way, if anyone does know of a good free / open source symbolic
> computer algebra system or programming language, please let me know.
> Mathematica is unbelievably expensive, and I don't need anything that
> powerful or comprehensive.
>

There are several.  Maxima and yacal come to my mind.  The wikipedia
article at http://en.wikipedia.org/wiki/Computer_algebra_system has a
list of propietary and open source algebra systems.  I can't really
say if they are very good, since I haven't used them seriously, but
i.e. when I took a glance at maxima, it seemed quite powerful.

Kristof

[q-lang-users] Q as a Computer Algebra System

[Rob H. <hub...@gm...>]

Hello Anthony,

I too first became interested in 'Q' because of mathematics. I am
fairly new to Q too.

Q is not, in my view, a typical functional language. If you're
interested in learning functional languages, you should also take a
look at some others. It would probably be instructive to try Standard
ML <http://www.smlnj.org/>. There are many other interesting
functional languages. However, I think you will really enjoy using Q.
It's one of the languages that I most enjoy using.

Beware that Q may not always behave quite as you expect at first. For
example, if you enter the simple program consisting of just the
rewrite rule:
    X+X = 2*X;
and the giving Q some expressions to reduce:
    ==> A+A+B
    2*A+B
    ==> A+B+B
    A+B+B
the final response from Q may not be what you expect.

A+B+B, which is (A+B)+B due to the left-associativity of (+), was not
reduced, as this does not match the given rule.
With the additional rule
    Y+X+X = Y+2*X;
you will now get the responses from the Q system
    ==> A+B+B
    A+2*B
    ==> A+A+B+B+C+C+D+D
    2*A+2*B+2*C+2*D

To quote Albert Graef's informative reply to one of my questions:
'Yes, it's surprisingly hard to do apparently basic stuff like this,
because it involves "rewriting modulo AC" (AC =
associativity/commutativity). The conventional way to deal with this
is to transform the original terms into a "sum of products" normal
form and represent that as a list which is lexicographically ordered
according to the involved symbols. It's not really that hard to do but
it indeed involves additional rules on a kind of meta-level, so there
is no straightforward solution with just a few equations.'

I was at first disappointed with Q not being the simple computer
algebra system I hoped it would be. But then that's not what it's
intended to be. Once you get used to it, you find that Q does seem to
do the "right thing". Those involved with developing Q take great care
to keep Q a sensible and consistent language. (See for example the
helpful reply from John Cowan in a discussion
<http://sourceforge.net/mailarchive/message.php?msg_id=19294969> of
type tests, in the lead up to the release of Q7.2)

Not many languages that I know are so well thought out, but I think
that Q is. And Q has fairly comprehensive libraries, together with
comprehensive programming tools, such as the debugger.

When I want to do some maths, I now usually reach for Q. But I tend to
write code for the specific type of mathematical object I'm currently
interested in. I imagine that to write a fairly comprehensive symbolic
computer algebra system would be a job of comparable complexity in any
language, Q, C++, ML, Python, or any other "general purpose" language.

By the way, if anyone does know of a good free / open source symbolic
computer algebra system or programming language, please let me know.
Mathematica is unbelievably expensive, and I don't need anything that
powerful or comprehensive.

I hope these comments (and opinions) are helpful,
Rob.

On 15/08/06, Anthony <ad...@ke...> wrote:
>
> Just a general question...Q is my first experience
> with a functional language.  What would it take to
> write a Mathematica clone in Q?
>
> I don't mean a full-Mathematica clone, but something
> that would emulate the kernel mode, circa 1988--an
> unlimited integer, numeric, graphical, and symbolic
> program with an easy syntax.
>
> For example x + 8  will generate internally a
> Plus[x,8] production, and 1+x^2+(y+z)^2 generates
>
> Plus[1, Power[x,2], Power[Plus[y,z],2]]
>
> What I'd like to do is just write a small Q program
> that parses a line of input according to the rules of
> Mathematica.  No need to evaluate the functions...just
> want to build a syntax checker at first.
>
> Or maybe I am dreaming...

[q-lang-users] Q as a Computer Algebra System

[Anthony <ad...@ke...>]

Just a general question...Q is my first experience
with a functional language.  What would it take to
write a Mathematica clone in Q?  

I don't mean a full-Mathematica clone, but something
that would emulate the kernel mode, circa 1988--an
unlimited integer, numeric, graphical, and symbolic
program with an easy syntax.

For example x + 8  will generate internally a
Plus[x,8] production, and 1+x^2+(y+z)^2 generates 

Plus[1, Power[x,2], Power[Plus[y,z],2]]

What I'd like to do is just write a small Q program
that parses a line of input according to the rules of
Mathematica.  No need to evaluate the functions...just
want to build a syntax checker at first.

Or maybe I am dreaming...

Re: [q-lang-users] ANN: Q 7.3 RC1 and Q Lex+Yacc 0.1 available

[Albert G. <Dr....@t-...>]

John Cowan wrote:
> I did a "make uninstall" from the q-7.2 directory, then removed q-7.3
> and remade it from the untouched tarball.  Same error.

Sorry, I have no idea right now. Neither libq nor clib has changed, and 
everything builds and runs fine under Linux, so I guess it must be some 
Windows-specific quirk. :( I'll try a Windows build asap to see whether 
I can reproduce this.

-- 
Dr. Albert Gr"af
Dept. of Music-Informatics, University of Mainz, Germany
Email:  Dr....@t-..., ag...@mu...
WWW:    http://www.musikinformatik.uni-mainz.de/ag

Re: [q-lang-users] ANN: Q 7.3 RC1 and Q Lex+Yacc 0.1 available

[John C. <co...@cc...>]

Albert Graef scripsit:
> Hi John,
> 
> that's strange because there weren't any changes in clib.q/c between 7.2 
> and 7.3 RC2. Are you sure that ../modules/clib built properly? Is there 
> maybe an old version of libq lying around somewhere that might be picked 
> up by the loader instead of the one in ../libq?

I did a "make uninstall" from the q-7.2 directory, then removed q-7.3
and remade it from the untouched tarball.  Same error.

-- 
After fixing the Y2K bug in an application:     John Cowan
        WELCOME TO <censored>                   co...@cc...
        DATE: MONDAK, JANUARK 1, 1900           http://www.ccil.org/~cowan

Re: [q-lang-users] ANN: Q 7.3 RC1 and Q Lex+Yacc 0.1 available

[Albert G. <Dr....@t-...>]

Hi John,

that's strange because there weren't any changes in clib.q/c between 7.2 
and 7.3 RC2. Are you sure that ../modules/clib built properly? Is there 
maybe an old version of libq lying around somewhere that might be picked 
up by the loader instead of the one in ../libq?

John Cowan wrote:
> Building on Cygwin crashes with:
> 
> make[2]: Entering directory `/opt/q-7.3/src'
> PATH=".:/home/JCowan/bin:/usr/local/ant/bin:/usr/java/j2sdk1.4.2_10/bin:/usr/local/bin:/usr/bin:/bin:/usr/X11R6/bin:/cygdrive/c/Perl/bin/:/cygdrive/c/WINDOWS/system32:/cygdrive/c/WINDOWS:/cygdrive/c/WINDOWS/System32/Wbem:/cygdrive/c/Program Files/ATI Technologies/ATI Control Panel:/cygdrive/c/Program Files/MySQL/MySQL Server 5.0/bin:/cygdrive/c/Program Files/QuickTime/QTSystem/:/cygdrive/c/Program Files/Microsoft SQL Server/90/Tools/binn/:/cygdrive/c/Program Files/Mondrian/bin:/bin:/usr/lib/lapack:/usr/local/bin/darcs" QPATH="../stdlib:../modules/clib:../modules/clib" ./q ./qcwrap.q ./qcwrap.q
> /opt/q-7.3/src/../modules/clib/clib.q: error loading module
> Warning: 267 unresolved external symbols
> ! File clib.q, line 297: Value mismatch in definition
> make[2]: *** [qcwrap.c] Error 2

-- 
Dr. Albert Gr"af
Dept. of Music-Informatics, University of Mainz, Germany
Email:  Dr....@t-..., ag...@mu...
WWW:    http://www.musikinformatik.uni-mainz.de/ag

Re: [q-lang-users] ANN: Q 7.3 RC1 and Q Lex+Yacc 0.1 available

[John C. <co...@cc...>]

Albert Graef scripsit:

> As usual, feedback is appreciated.

Building on Cygwin crashes with:

make[2]: Entering directory `/opt/q-7.3/src'
PATH=".:/home/JCowan/bin:/usr/local/ant/bin:/usr/java/j2sdk1.4.2_10/bin:/usr/local/bin:/usr/bin:/bin:/usr/X11R6/bin:/cygdrive/c/Perl/bin/:/cygdrive/c/WINDOWS/system32:/cygdrive/c/WINDOWS:/cygdrive/c/WINDOWS/System32/Wbem:/cygdrive/c/Program Files/ATI Technologies/ATI Control Panel:/cygdrive/c/Program Files/MySQL/MySQL Server 5.0/bin:/cygdrive/c/Program Files/QuickTime/QTSystem/:/cygdrive/c/Program Files/Microsoft SQL Server/90/Tools/binn/:/cygdrive/c/Program Files/Mondrian/bin:/bin:/usr/lib/lapack:/usr/local/bin/darcs" QPATH="../stdlib:../modules/clib:../modules/clib" ./q ./qcwrap.q ./qcwrap.q
/opt/q-7.3/src/../modules/clib/clib.q: error loading module
Warning: 267 unresolved external symbols
! File clib.q, line 297: Value mismatch in definition
make[2]: *** [qcwrap.c] Error 2

-- 
But that, he realized, was a foolish            John Cowan
thought; as no one knew better than he          co...@cc...
that the Wall had no other side.                http://www.ccil.org/~cowan
        --Arthur C. Clarke, "The Wall of Darkness"

Re: [q-lang-users] quote evaluation

[Kristof B. <kr...@vl...>]

Albert Graef <Dr....@t-...> writes:
> Kristof Bastiaensen wrote:
>> If I get a working version of my html library, I'll let it know, and
>> post it somewhere!
>
> That would be nice. I could also upload it to q-lang.sf.net and make it 
> available in the "grab bag" if you want.
>

Yes, that would be nice, once I finish it.  At the moment it is still
quite modest though, I'll need to add a bit of functionality, and
check that it doesn't have bugs...

Regards,
Kristof

Re: [q-lang-users] quote evaluation

[Albert G. <Dr....@t-...>]

Kristof Bastiaensen wrote:
> If I get a working version of my html library, I'll let it know, and
> post it somewhere!

That would be nice. I could also upload it to q-lang.sf.net and make it 
available in the "grab bag" if you want.

Cheers,
Albert

-- 
Dr. Albert Gr"af
Dept. of Music-Informatics, University of Mainz, Germany
Email:  Dr....@t-..., ag...@mu...
WWW:    http://www.musikinformatik.uni-mainz.de/ag

Re: [q-lang-users] quote evaluation

[Kristof B. <kr...@vl...>]

> ---- snip -------
>> However I came across the following strange behaviour.  In the
>> equation: 
>> 
>>   test '(A B) = ('A, 'B);
>> 
>> I would expect test '(a (2 + 3)) to evaluate to ('a, '(2 + 3)),
>> however it evaluates to ('a, '5).  Is this the defined behaviour?
> 
> Yes, it is, but only since Q 7.1. The general rule is that, while
> special arguments of a function will never be evaluated, deferred
> subterms inside a _non-special_ arg are evaluated automatically when
> they are needed in the pattern matching process. This is a
> convenience so that non-special functions can assume matched
> subterms to be in (weak) normal form, which is important to make
> functions operating on lazy data structures such as streams do the
> right thing.

Yes, it makes more sense now!

>> Also, when using the Q interpreter to write scripts, it always
>> prints the last object to stdout.  Is there an option to turn it
>> off?  If I want to write a script that outputs some text, I
>> wouldn't want the output to be clobbered with an object.
> 
> Explicitly exiting from the program with `exit 0' probably does what
> you want.

Thanks, that does the trick.
If I get a working version of my html library, I'll let it know, and
post it somewhere!

Regards,
Kristof

[q-lang-users] ANN: Q 7.3 RC1 and Q Lex+Yacc 0.1 available

[Albert G. <Dr....@t-...>]

Hi,

I've just uploaded the first candidate for the upcoming Q 7.3 release 
(source tarball and rpms), featuring the change in the semantics of 
const discussed on the list as well as several bugfixes. You can find it 
here:

http://sourceforge.net/project/showfiles.php?group_id=96881&package_id=188958&release_id=439339

Also available at the same location is my first version of Q Yacc and 
Lex (100% Q, no C Yacc/Lex is required to run these). Note that Q 
Yacc/Lex needs Q 7.3. I still need to work on the performance of the 
yylex function, but if you don't care too much about speed then the 
current snapshot already works very nicely. Preliminary documentation is 
in the README file and the obligatory desktop calculator example is also 
included. Enjoy! :)

As usual, feedback is appreciated.

Cheers,
Albert

-- 
Dr. Albert Gr"af
Dept. of Music-Informatics, University of Mainz, Germany
Email:  Dr....@t-..., ag...@mu...
WWW:    http://www.musikinformatik.uni-mainz.de/ag

[q-lang-users] lists.sourceforge.net news letter

[Roy J. <Haw...@my...>]

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Re: [q-lang-users] quote evaluation

[Albert G. <Dr....@t-...>]

Hi Kristof, and welcome to the list!

> However I came across the following strange behaviour.  In the
> equation: 
> 
>   test '(A B) = ('A, 'B);
> 
> I would expect test '(a (2 + 3)) to evaluate to ('a, '(2 + 3)),

Just make `test' a special form, then you get the behaviour that you 
want, see below.

> however it evaluates to ('a, '5).  Is this the defined behaviour?

Yes, it is, but only since Q 7.1. The general rule is that, while 
special arguments of a function will never be evaluated, deferred 
subterms inside a _non-special_ arg are evaluated automatically when 
they are needed in the pattern matching process. This is a convenience 
so that non-special functions can assume matched subterms to be in 
(weak) normal form, which is important to make functions operating on 
lazy data structures such as streams do the right thing.

For instance, consider the following definition:

deinterleave {}		= {};
deinterleave {X,Y|Xs}	= {(X,Y)|deinterleave Xs};

To match the left-hand side of the second rule (which is actually a 
shorthand for {X|{Y|Xs}}, the pattern matcher has to evaluate the tail 
of the actual stream parameter. Note that otherwise this equation would 
never match a stream with deferred tail like {1..} = {1|iterate (+1) 
((+1) 1)}.

This only happens when a pattern reaches inside a deferred subterm. If 
you have an equation like

test 'X = '(X+1);

then X is _not_ evaluated, because it is unnecessary to decide the match:

==> test '(2 + 3)
'(2+3+1)

But in your example

test '(A B) = ('A, 'B);

the pattern reaches inside the argument of ('), so the pattern matcher 
evaluates the argument to decide whether this value is an application or 
not. (') is handled just like any other special data constructor here.

OTOH, if you make test itself a special form, then argument evaluation 
is always inhibited and arguments are passed as is. So the following 
will do what you want:

special test X;
test '(A B) = ('A, 'B);

Example:

==> test '(a (2 + 3))
('a,'(2+3))

I know that this is somewhat confusing, and in a program I recently 
wrote I also ran into the very same trap. ;-) But this new "call by 
need" way of doing pattern matching makes defining functions operating 
on lazy data structures so much more convenient.

> Also, when using the Q interpreter to write scripts, it always prints
> the last object to stdout.  Is there an option to turn it off?  If
> I want to write a script that outputs some text, I wouldn't want the
> output to be clobbered with an object.

Explicitly exiting from the program with `exit 0' probably does what you 
want.

Cheers,
Albert

-- 
Dr. Albert Gr"af
Dept. of Music-Informatics, University of Mainz, Germany
Email:  Dr....@t-..., ag...@mu...
WWW:    http://www.musikinformatik.uni-mainz.de/ag

[q-lang-users] quote evaluation

[Kristof B. <kr...@vl...>]

Hi,

first I'd like to say that Q is an interesting language, and it is
surprising to find such a complete documentation for a relatively
unknown language.  I find special forms particularly interesting.  I
wrote part of a library to write html pages as expressions, where you
can write an html tag as function application (like scheme sxml).

For example:

(to_html
  (html
   (head (title ~Homepage))
   (body
    (h1 ~Title)
    (a (href = "www.url.org/adress")
     "ref"))))

=> a nested html object

However I came across the following strange behaviour.  In the
equation: 

  test '(A B) = ('A, 'B);

I would expect test '(a (2 + 3)) to evaluate to ('a, '(2 + 3)),
however it evaluates to ('a, '5).  Is this the defined behaviour?
I would think that quote is a special form which doesn't evaluate
it's argument.

Also, when using the Q interpreter to write scripts, it always prints
the last object to stdout.  Is there an option to turn it off?  If
I want to write a script that outputs some text, I wouldn't want the
output to be clobbered with an object.

Regards,
Kristof Bastiaensen

[q-lang-users] automated response

[Qiana B. <q....@th...>]

Re: [q-lang-users] The implicit operator in Q

[John C. <co...@cc...>]

Albert Graef scripsit:

> So, if you have an expression of the form bin X T1 T2 you can still be 
> sure that it is a normal form. I guess that this solves your problem?

Yes, it does.  Thanks.

> OTOH, the following equation is now valid:
> 
> bin X T1 T2 Y = ...;
> 
> Which makes sense if you want to also be able to use an (essentially 
> equivalent) equation like:
> 
> T:Bintree Y = ...;

Good.

-- 
Yes, chili in the eye is bad, but so is your    John Cowan
ear.  However, I would suggest you wash your    co...@cc...
hands thoroughly before going to the toilet.    http://www.ccil.org/~cowan
        --gadicath

Re: [q-lang-users] The implicit operator in Q

[Albert G. <Dr....@t-...>]

John Cowan wrote:
> This makes me a bit nervous.  Would it be possible to distinguish
> between constants and constructors, and allow a constant in the head
> (but not all constants) while still forbidding a constructor?

That would be a rather arbitrary distinction between constructors of 
zero and nonzero arity.

> The whole point of constructors is that the application of a constructor
> is guaranteed to be in normal form.

Given a declaration like "type BinTree = const bin X T1 T2;" you still 
have that the following equations are all forbidden:

bin = ...;
bin X = ...;
bin X T1 = ...;
bin X T1 T2 = ...;

So, if you have an expression of the form bin X T1 T2 you can still be 
sure that it is a normal form. I guess that this solves your problem?

OTOH, the following equation is now valid:

bin X T1 T2 Y = ...;

Which makes sense if you want to also be able to use an (essentially 
equivalent) equation like:

T:Bintree Y = ...;

I've already implemented it that way, and I've also updated the 
documentation in qdoc.texi. Seems to work nicely so far. If you want to 
try it out, just get yourself the latest qcrules.c from cvs and recompile.

Cheers,
Albert

-- 
Dr. Albert Gr"af
Dept. of Music-Informatics, University of Mainz, Germany
Email:  Dr....@t-..., ag...@mu...
WWW:    http://www.musikinformatik.uni-mainz.de/ag

Re: [q-lang-users] The implicit operator in Q

[John C. <co...@cc...>]

Albert Graef scripsit:

> Considering the potential use of application as a kind of "default 
> operator", as you discussed, I'm beginning to wonder whether this 
> constraint, that a const value cannot occur in the head of a lhs, is a 
> bit too strict. Maybe the constraint should actually be "the (entire) 
> lhs must not be a const", so that constructor equations like [1,2,3] = 
> [] are still forbidden, but not applications involving a const in the 
> head like [X|Xs] Y = ...?
> 
> I actually like this idea. It would cure the inconsistency I described 
> in my previous post, and I'd say that it also follows the principle of 
> the least surprise; there's no real reason why a constant data object 
> cannot be something that acts like a function which can be applied to an 
> argument. Of course, this also gives you a bigger gun to shoot yourself 
> in the foot... But, as Keith rightfully pointed out, Q is not a "safer 
> programming" language anyway.

This makes me a bit nervous.  Would it be possible to distinguish
between constants and constructors, and allow a constant in the head
(but not all constants) while still forbidding a constructor?
The whole point of constructors is that the application of a constructor
is guaranteed to be in normal form.

-- 
What is the sound of Perl?  Is it not the       John Cowan
sound of a [Ww]all that people have stopped     co...@cc...
banging their head against?  --Larry            http://www.ccil.org/~cowan

Re: [q-lang-users] The implicit operator in Q

[Keith T. <kaz...@ea...>]

--- Albert Graef writes:
- Maybe the constraint should actually be "the (entire) lhs must
- not be a const", so that constructor equations like [1,2,3] = []
- are still forbidden, but not applications involving a const in the
- head like [X|Xs] Y = ...?
- 
- [snip!]
- 
- I actually like this idea.

Me too.

- This also gives you a bigger gun to shoot yourself in the foot...

If it is a _well-documented_ gun, then it should not be a problem.

Cheers,
Keith 

Re: [q-lang-users] The implicit operator in Q

[Albert G. <Dr....@t-...>]

John Cowan wrote:
> Albert Graef scripsit:
> 
>>4. be happy that Q still leaves some dirty tricks to be discovered by 
>>the master Q programmer ;-)
> 
> Indeed, though I think this particular trick could now be documented
> in the manual.

Yes, there should be a list of exactly what can and what cannot occur on 
the lhs of an equation. I already put this on my TODO list.

Considering the potential use of application as a kind of "default 
operator", as you discussed, I'm beginning to wonder whether this 
constraint, that a const value cannot occur in the head of a lhs, is a 
bit too strict. Maybe the constraint should actually be "the (entire) 
lhs must not be a const", so that constructor equations like [1,2,3] = 
[] are still forbidden, but not applications involving a const in the 
head like [X|Xs] Y = ...?

I actually like this idea. It would cure the inconsistency I described 
in my previous post, and I'd say that it also follows the principle of 
the least surprise; there's no real reason why a constant data object 
cannot be something that acts like a function which can be applied to an 
argument. Of course, this also gives you a bigger gun to shoot yourself 
in the foot... But, as Keith rightfully pointed out, Q is not a "safer 
programming" language anyway.

Albert

-- 
Dr. Albert Gr"af
Dept. of Music-Informatics, University of Mainz, Germany
Email:  Dr....@t-..., ag...@mu...
WWW:    http://www.musikinformatik.uni-mainz.de/ag