Re: Spaces please!

Re: Spaces please!

[Pascal J. Bourguignon]

andrea <andrea.crotti.0@gmail.com> writes:

> I get sick sometimes to read something like
> x=y+1*(2-3*a^2)
> but I get even more sick to add spaces manually every time.

Funny.  I get sick reading something like 

  x = y+1 * ( 2-3 * a   ^2)

;-)

Perhaps the best form would be:

  (= x
    (+ y
       (* 1
          (- 2
             (* 3
                (^ a 2))))))


but that would be a different syntax.  Notice that it could be the
work of an editor to read a source in whatever "syntax" it may happen
to be, to present it to the user in whatever form the user prefers,
allowing it to do structural editing instead of textual edition, and
saving it back to whatever "syntax" is required. 

A little like it is done for character encodings, where you can load a
file in iso-2022, edit it in emacs unicode, and save it in utf-8, only
for language syntaxes.

But that'd be a whole project.



> I ask help to you elisp gurus, should I use a regexp 

No, you cannot parse arithmetic expressions with regular expressions,
they are too weak!  You need a parser.


> or a macro-like
> function (go-here, do-this)?
>
> I think I should define some rules like:
> - which operators want spaces (and if before or after)
> - what is the arity of them
>
> One problem for example could arise from things like
>
> (-2)^10
> but we could have some operators that could be binary or unary and check
> that somehow.
>
> Someone has done it already maybe?

Well, you could hack something half working yourself, or perhaps you
could use a predefined parser for the language in question.

http://cedet.sourceforget.net  has a parser generator (the
"bovinator", and parsers predefined for a number of programming
languages, that you could use to implement your "formula beautifier".
Once you have the parse tree, it is indeed trivial to generate the
expression with the number of spaces you want.


-- 
__Pascal Bourguignon__

Re: Spaces please!

[Harald Hanche-Olsen]

+ pjb@informatimago.com (Pascal J. Bourguignon):

> Perhaps the best form would be:
>
>   (= x
>     (+ y
>        (* 1
>           (- 2
>              (* 3
>                 (^ a 2))))))

Who needs stinkin' parentheses? Polish notation is the way to go.

  =x+y*1-2*3^a2

> but that would be a different syntax.

Oh. Well, never mind then.

-- 
* Harald Hanche-Olsen     <URL:http://www.math.ntnu.no/~hanche/>
- It is undesirable to believe a proposition
  when there is no ground whatsoever for supposing it is true.
  -- Bertrand Russell

Re: Spaces please!

[Lennart Borgman]

On Tue, Dec 1, 2009 at 6:06 PM, Pascal J. Bourguignon
<pjb@informatimago.com> wrote:
>
> No, you cannot parse arithmetic expressions with regular expressions,
> they are too weak!  You need a parser.


Some recursion + reg exps?

Re: Spaces please!

[Burkhard Schultheis]

Am 01.12.2009 17:19, schrieb andrea:
>
> I get sick sometimes to read something like
> x=y+1*(2-3*a^2)
> but I get even more sick to add spaces manually every time.
> I ask help to you elisp gurus, should I use a regexp or a macro-like
> function (go-here, do-this)?
>
> I think I should define some rules like:
> - which operators want spaces (and if before or after)
> - what is the arity of them
>
> One problem for example could arise from things like
>
> (-2)^10
> but we could have some operators that could be binary or unary and check
> that somehow.

I would do it with a beautifier like uncrustify with GUI universalident 
(<http://sourceforge.net/projects/universalindent/>. It can do that and 
much, much more!

Regards
Burkhard

Re: Spaces please!

[Burkhard Schultheis]

Am 01.12.2009 19:21, schrieb Burkhard Schultheis:
> Am 01.12.2009 17:19, schrieb andrea:
>>
>> I get sick sometimes to read something like
>> x=y+1*(2-3*a^2)
>> but I get even more sick to add spaces manually every time.
>> I ask help to you elisp gurus, should I use a regexp or a macro-like
>> function (go-here, do-this)?
>>
>> I think I should define some rules like:
>> - which operators want spaces (and if before or after)
>> - what is the arity of them
>>
>> One problem for example could arise from things like
>>
>> (-2)^10
>> but we could have some operators that could be binary or unary and check
>> that somehow.
>
> I would do it with a beautifier like uncrustify with GUI universalident
> (<http://sourceforge.net/projects/universalindent/>. It can do that and
> much, much more!
>
> Regards
> Burkhard

... but these programs do it for source code files, I think. ;-)

Spaces please!

[andrea]

I get sick sometimes to read something like
x=y+1*(2-3*a^2)
but I get even more sick to add spaces manually every time.
I ask help to you elisp gurus, should I use a regexp or a macro-like
function (go-here, do-this)?

I think I should define some rules like:
- which operators want spaces (and if before or after)
- what is the arity of them

One problem for example could arise from things like

(-2)^10
but we could have some operators that could be binary or unary and check
that somehow.

Someone has done it already maybe?

Re: Spaces please!

[Thien-Thi Nguyen]

() andrea <andrea.crotti.0@gmail.com>
() Tue, 01 Dec 2009 17:19:30 +0100

   Someone has done it already maybe?

Indeed!  Try looking at:
  (info "(calc) Language Modes")

I imagine the parsed (and unparsed) form of
an expression could be displayed as an overlay.

thi