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space vs semicolon - why syntax error with the former ? (octave-3.4.2)

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space vs semicolon - why syntax error with the former ? (octave-3.4.2)

Sergei Steshenko
Hello,

here is a screen session:
"
octave:1> for ii=1:1 ii endfor disp(ii)
parse error:

  syntax error

>>> for ii=1:1 ii endfor disp(ii)
                            ^

octave:1> for ii=1:1 ii endfor;disp(ii)
ii =  1
 1
octave:2>
".

Why is it so 'octave' doesn't accept the first variant ?

With "traditional" 'endfor' on a new line semicolon isn't needed ?
Is there any reason for newline whitespace to be treated differently than space whitespace ?

Thanks,
  Sergei.
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Re: space vs semicolon - why syntax error with the former ? (octave-3.4.2)

bpabbott
Administrator
On Aug 16, 2011, at 7:25 AM, Sergei Steshenko wrote:

> Hello,
>
> here is a screen session:
> "
> octave:1> for ii=1:1 ii endfor disp(ii)
> parse error:
>
>  syntax error
>
>>>> for ii=1:1 ii endfor disp(ii)
>                            ^
>
> octave:1> for ii=1:1 ii endfor;disp(ii)
> ii =  1
> 1
> octave:2>
> ".
>
> Why is it so 'octave' doesn't accept the first variant ?
>
> With "traditional" 'endfor' on a new line semicolon isn't needed ?
> Is there any reason for newline whitespace to be treated differently than space whitespace ?
>
> Thanks,
>  Sergei.

The parser treats keywords and functions differently.

I am not familiar with the parser implementation, so I can't give a better explanation. To see what Octave's keywords are, you can use the undocumented function __keywords__.

To see what functions are in the path, use __list_functions__.  There are builtin function as well. To see those use __builtins__.

Ben

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Re: space vs semicolon - why syntax error with the former ? (octave-3.4.2)

Sergei Steshenko


--- On Tue, 8/16/11, Ben Abbott <[hidden email]> wrote:

> From: Ben Abbott <[hidden email]>
> Subject: Re: space vs semicolon - why syntax error with the former ? (octave-3.4.2)
> To: "Sergei Steshenko" <[hidden email]>
> Cc: [hidden email]
> Date: Tuesday, August 16, 2011, 4:55 AM
> On Aug 16, 2011, at 7:25 AM, Sergei
> Steshenko wrote:
>
> > Hello,
> >
> > here is a screen session:
> > "
> > octave:1> for ii=1:1 ii endfor disp(ii)
> > parse error:
> >
> >  syntax error
> >
> >>>> for ii=1:1 ii endfor disp(ii)
> >               
>             ^
> >
> > octave:1> for ii=1:1 ii endfor;disp(ii)
> > ii =  1
> > 1
> > octave:2>
> > ".
> >
> > Why is it so 'octave' doesn't accept the first variant
> ?
> >
> > With "traditional" 'endfor' on a new line semicolon
> isn't needed ?
> > Is there any reason for newline whitespace to be
> treated differently than space whitespace ?
> >
> > Thanks,
> >  Sergei.
>
> The parser treats keywords and functions differently.
>
> I am not familiar with the parser implementation, so I
> can't give a better explanation. To see what Octave's
> keywords are, you can use the undocumented function
> __keywords__.
>
> To see what functions are in the path, use
> __list_functions__.  There are builtin function as
> well. To see those use __builtins__.
>
> Ben
>
>

I do not grasp your reply. My point is that in "normal" languages all
whitespaces are created equal. So, since the following works:

"
octave:1> for ii = 1:1
>   ii
> endfor
ii =  1
octave:2> disp(ii);
 1
octave:3>          
"

, and in this case 'endfor' is separated from 'disp' by newline, I  also
expect

"
octave:3> for ii = 1:1 ii endfor disp(ii);
parse error:

  syntax error

>>> for ii = 1:1 ii endfor disp(ii);
                              ^

octave:3>    
",

to work (because newline and space both look like created equal whitespaces to me), but it doesn't.

Thanks,
  Sergei.
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Re: space vs semicolon - why syntax error with the former ? (octave-3.4.2)

bpabbott
Administrator

On Aug 16, 2011, at 8:03 AM, Sergei Steshenko wrote:

>
>
> --- On Tue, 8/16/11, Ben Abbott <[hidden email]> wrote:
>
>> From: Ben Abbott <[hidden email]>
>> Subject: Re: space vs semicolon - why syntax error with the former ? (octave-3.4.2)
>> To: "Sergei Steshenko" <[hidden email]>
>> Cc: [hidden email]
>> Date: Tuesday, August 16, 2011, 4:55 AM
>> On Aug 16, 2011, at 7:25 AM, Sergei
>> Steshenko wrote:
>>
>>> Hello,
>>>
>>> here is a screen session:
>>> "
>>> octave:1> for ii=1:1 ii endfor disp(ii)
>>> parse error:
>>>
>>>   syntax error
>>>
>>>>>> for ii=1:1 ii endfor disp(ii)
>>>                
>>             ^
>>>
>>> octave:1> for ii=1:1 ii endfor;disp(ii)
>>> ii =  1
>>> 1
>>> octave:2>
>>> ".
>>>
>>> Why is it so 'octave' doesn't accept the first variant
>> ?
>>>
>>> With "traditional" 'endfor' on a new line semicolon
>> isn't needed ?
>>> Is there any reason for newline whitespace to be
>> treated differently than space whitespace ?
>>>
>>> Thanks,
>>>   Sergei.
>>
>> The parser treats keywords and functions differently.
>>
>> I am not familiar with the parser implementation, so I
>> can't give a better explanation. To see what Octave's
>> keywords are, you can use the undocumented function
>> __keywords__.
>>
>> To see what functions are in the path, use
>> __list_functions__.  There are builtin function as
>> well. To see those use __builtins__.
>>
>> Ben
>
> I do not grasp your reply. My point is that in "normal" languages all
> whitespaces are created equal. So, since the following works:
>
> "
> octave:1> for ii = 1:1
>>  ii
>> endfor
> ii =  1
> octave:2> disp(ii);
> 1
> octave:3>          
> "
>
> , and in this case 'endfor' is separated from 'disp' by newline, I  also
> expect
>
> "
> octave:3> for ii = 1:1 ii endfor disp(ii);
> parse error:
>
>  syntax error
>
>>>> for ii = 1:1 ii endfor disp(ii);
>                              ^
> octave:3>    
> ",
>
> to work (because newline and space both look like created equal whitespaces to me), but it doesn't.
>
> Thanks,
>  Sergei.

As I said, I am not familiar with the parser. What I did notice is that the parser is treating keywords differently than functions.

I am also aware of a  feature of both Matlab and Octave that means all space are not equal. Consider that each of the commands below are valid syntax.

        disp("Hello World")

... and ...

        disp ("Hello World")

... and ...

        disp "Hello World"

Also consider that each of the commands below are also valid syntax

        ("Hello World")

        "Hello World"

In Octave/Matlab spaces are not equal.

Back to your example, there is more than one interpretation of ...

        for ii = 1:1 ii endfor disp ii ;

Ben



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Re: space vs semicolon - why syntax error with the former ? (octave-3.4.2)

Jordi Gutiérrez Hermoso-2
In reply to this post by Sergei Steshenko
A newline is the end of a statement. If you want to end statements in
the same line, you use semicolons or commas. You always use semicolons
if you want to end a statement and not echo its result and commas if
you don't.

Octave is hardly the only language that works this way; bash comes to
mind as another language where you need to write, e.g.

     for i in *; do foo $i; done; echo "done"

and if you miss the semicolon after done, it's a syntax error in bash,
similar to Octave.

HTH,
- Jordi G. H.
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Re: space vs semicolon - why syntax error with the former ? (octave-3.4.2)

Sergei Steshenko
In reply to this post by bpabbott


--- On Tue, 8/16/11, Ben Abbott <[hidden email]> wrote:

> From: Ben Abbott <[hidden email]>
> Subject: Re: space vs semicolon - why syntax error with the former ? (octave-3.4.2)
> To: "Sergei Steshenko" <[hidden email]>
> Cc: [hidden email]
> Date: Tuesday, August 16, 2011, 5:24 AM


> Back to your example, there is more than one interpretation
> of ...
>
>     for ii = 1:1 ii endfor disp ii ;
>
> Ben
>

'endfor' "balances" 'for', i.e. the parser may forget _completely_ (except
for input text pointer position) about the whole 'for' loop, and after
that parse the 'disp' (in this case) part.

I.e. I still don't see how different interpretation can be present in
this case - to me it looks like the 'for' loop statement is unambiguously
over, and no special separator (e.g. ';') is necessary - simply
because of 'endfor' detection.

Regards,
  Sergei.

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Re: space vs semicolon - why syntax error with the former ? (octave-3.4.2)

CdeMills
Sergei Steshenko-2 wrote
--- On Tue, 8/16/11, Ben Abbott <[hidden email]> wrote:


> Back to your example, there is more than one interpretation
> of ...
>
>     for ii = 1:1 ii endfor disp ii ;
>
> Ben
>

'endfor' "balances" 'for', i.e. the parser may forget _completely_ (except
for input text pointer position) about the whole 'for' loop, and after
that parse the 'disp' (in this case) part.

I.e. I still don't see how different interpretation can be present in
this case - to me it looks like the 'for' loop statement is unambiguously
over, and no special separator (e.g. ';') is necessary - simply
because of 'endfor' detection.
Sorry, but taking your reasoning literally is bogus: let's consider
 if (0>1) disp('Problem'); end; disp(36)
if you take for granted that the 'end' close the expression, then then previous line should be equivalent to
 ; disp(36)
which is a syntactically incorrect.

Regards

Pascal
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Re: space vs semicolon - why syntax error with the former ? (octave-3.4.2)

Sergei Steshenko


--- On Tue, 8/16/11, CdeMills <[hidden email]> wrote:

> From: CdeMills <[hidden email]>
> Subject: Re: space vs semicolon - why syntax error with the former ? (octave-3.4.2)
> To: [hidden email]
> Date: Tuesday, August 16, 2011, 10:03 AM
>
> Sergei Steshenko-2 wrote:
> >
> > --- On Tue, 8/16/11, Ben Abbott &lt;[hidden email]&gt;
> wrote:
> >
> >
> >> Back to your example, there is more than one
> interpretation
> >> of ...
> >>
> >>     for ii = 1:1 ii endfor disp ii ;
> >>
> >> Ben
> >>
> >
> > 'endfor' "balances" 'for', i.e. the parser may forget
> _completely_ (except
> > for input text pointer position) about the whole 'for'
> loop, and after
> > that parse the 'disp' (in this case) part.
> >
> > I.e. I still don't see how different interpretation
> can be present in
> > this case - to me it looks like the 'for' loop
> statement is unambiguously
> > over, and no special separator (e.g. ';') is necessary
> - simply
> > because of 'endfor' detection.
> >
> >
>
> Sorry, but taking your reasoning literally is bogus: let's
> consider
>  if (0>1) disp('Problem'); end; disp(36)
> if you take for granted that the 'end' close the
> expression, then then
> previous line should be equivalent to
>  ; disp(36)
> which is a syntactically incorrect.
>
> Regards
>
> Pascal
>
> --
> View this message in context: http://octave.1599824.n4.nabble.com/space-vs-semicolon-why-syntax-error-with-the-former-octave-3-4-2-tp3746937p3747777.html
> Sent from the Octave - General mailing list archive at
> Nabble.com.


And why should it be syntactically incorrect in the first place ?

E.g.:

"
sergei@amdam2:~/junk> perl -e ';print "36\n"'
36
sergei@amdam2:~/junk>
".

Or:

"
sergei@amdam2:~/junk/semicolon_in_c> cat -n main.c
     1  #include <stdio.h>
     2
     3  int main()
     4    {
     5    ;printf("%u\n", 36u);
     6    return 0;
     7    }
sergei@amdam2:~/junk/semicolon_in_c> ~/AFSWD/install/gcc-4.4.6/binsh/gcc -Wall -Wextra main.c
sergei@amdam2:~/junk/semicolon_in_c> ./a.out
36
sergei@amdam2:~/junk/semicolon_in_c>  
".

Normal languages do not care about semicolon before a function call.

Regards,
  Sergei.
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Re: space vs semicolon - why syntax error with the former ? (octave-3.4.2)

Przemek Klosowski-7
On 08/16/2011 01:52 PM, Sergei Steshenko wrote:
> this case - to me it looks like the 'for' loop
> statement is unambiguously
> over, and no special separator (e.g. ';') is necessary

> --- On Tue, 8/16/11, CdeMills<[hidden email]>  wrote:
>> Sorry, but taking your reasoning literally is bogus: let's
>> consider
>>   if (0>1) disp('Problem'); end; disp(36)
>> if you take for granted that the 'end' close the
>> expression, then then
>> previous line should be equivalent to
>>   ; disp(36)
>> which is a syntactically incorrect.

> Normal languages do not care about semicolon before a function call.

There is no such thing as a 'normal language' in this respect. Look up
the debate that raged in the nineties on whether semicolon should be a
separator or a terminator. One doesn't have to look far, this is covered
in Wikipedia:

http://en.wikipedia.org/wiki/Comparison_of_programming_languages_%28syntax%29

There are arguments for either style, and the debate ended in a tie---it
appears that the score among the languages listed in the Wikipedia
article is 24:21.

Matlab happens to be one of the few languages with both a primary
(newline) and secondary (';,') separator---probably to make it easier
for command line coding; they also overloaded the semicolon to control
output silencing. It is what it is, let's get on with it :)

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Re: space vs semicolon - why syntax error with the former ? (octave-3.4.2)

Sergei Steshenko


--- On Tue, 8/16/11, Przemek Klosowski <[hidden email]> wrote:

> From: Przemek Klosowski <[hidden email]>
> Subject: Re: space vs semicolon - why syntax error with the former ? (octave-3.4.2)
> To: [hidden email]
> Date: Tuesday, August 16, 2011, 11:33 AM
> On 08/16/2011 01:52 PM, Sergei
> Steshenko wrote:
> > this case - to me it looks like the 'for' loop
> > statement is unambiguously
> > over, and no special separator (e.g. ';') is
> necessary
>
> > --- On Tue, 8/16/11, CdeMills<[hidden email]
> wrote:
> >> Sorry, but taking your reasoning literally is
> bogus: let's
> >> consider
> >>   if (0>1) disp('Problem'); end;
> disp(36)
> >> if you take for granted that the 'end' close the
> >> expression, then then
> >> previous line should be equivalent to
> >>   ; disp(36)
> >> which is a syntactically incorrect.
>
> > Normal languages do not care about semicolon before a
> function call.
>
> There is no such thing as a 'normal language' in this
> respect. Look up the debate that raged in the nineties on
> whether semicolon should be a separator or a terminator. One
> doesn't have to look far, this is covered in Wikipedia:
>
> http://en.wikipedia.org/wiki/Comparison_of_programming_languages_%28syntax%29
>
> There are arguments for either style, and the debate ended
> in a tie---it appears that the score among the languages
> listed in the Wikipedia article is 24:21.
>
> Matlab happens to be one of the few languages with both a
> primary (newline) and secondary (';,') separator---probably
> to make it easier for command line coding; they also
> overloaded the semicolon to control output silencing. It is
> what it is, let's get on with it :)
>
> _______________________________________________
> Help-octave mailing list
> [hidden email]
> https://mailman.cae.wisc.edu/listinfo/help-octave
>

I am widening my question: why comma is more acceptable than space too:

"
octave:1> for ii = 1:1 ii endfor,disp(ii);
ii =  1
 1
octave:2>  
"
?

I still want to see a _logical_ argument about unacceptability of space
in this case.

I reiterate my point: as soon as 'endfunction' is detected, it doesn't
matter that the loop has been found from the point of view of parser.

To me insistence on semicolon or comma or newline and unacceptability of
space (and tab) is an unnecessary nuisance.

Computer languages are formal ones compared to human languages - in order
to achieve disambiguation. I do not see an ambiguity in such a case in the
first place - end of 'for' statement is easily detected by parsing
'endfor' keyword.

Thanks,
  Sergei.


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Re: space vs semicolon - why syntax error with the former ? (octave-3.4.2)

Jordi Gutiérrez Hermoso-2
On 16 August 2011 17:13, Sergei Steshenko <[hidden email]> wrote:

> I am widening my question: why comma is more acceptable than space too:
>
> "
> octave:1> for ii = 1:1 ii endfor,disp(ii);
> ii =  1
>  1
> octave:2>
> "
> ?
>
> I still want to see a _logical_ argument about unacceptability of space
> in this case.

Languages have syntax. If you prefer to not have the least syntax
possible, use lisp. Btw, Perl, which you seem to think of as a normal
language, has the weird quirk that if($foo) do_bar(); is a syntax
error and instead you need if($foo) {do_bar();} for no good reason. C
and C++ don't need the extra braces, but Perl does (Perl also needs a
lot of other unnecessary things, like making the user spell out
explicitly if something is a reference or a value). Python has
whitespace. C++ has templates. Octave has semicolons.

Facts of life.

If you want to make Octave a normal language, patches are probably welcome:

     http://hg.savannah.gnu.org/hgweb/octave/file/b80b18f537ca/src/oct-parse.yy

- Jordi G. H.
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Re: space vs semicolon - why syntax error with the former ? (octave-3.4.2)

CdeMills
In reply to this post by Sergei Steshenko
Sergei Steshenko-2 wrote
Hello,

here is a screen session:
"
octave:1> for ii=1:1 ii endfor disp(ii)
parse error:

  syntax error

>>> for ii=1:1 ii endfor disp(ii)
                            ^

octave:1> for ii=1:1 ii endfor;disp(ii)
ii =  1
 1
octave:2>
".

Why is it so 'octave' doesn't accept the first variant ?

With "traditional" 'endfor' on a new line semicolon isn't needed ?
Is there any reason for newline whitespace to be treated differently than space whitespace ?
1) there is no such thing as a newline whitespace. It's a newline terminator.
2) some keywords stop the parsing of the _previous_ expression: else, end, ...
3) the logic is that, if you require to pack on one line:
a = 3
b = 2
you have the choice between
a = 3; b = 2
or
a = 3, b = 2
This way, to pack
if (1> 0) c=3 else d=4 end
a = 3
You need either
if (1> 0) c=3 else d=4 end, a = 3
or
if (1> 0) c=3 else d=4 end; a = 3
My interpretation is that ';,' used as secondary separator must come where the primary separator (newline) is expected.

Quite franckly, I expect to make some keywords (end, endfor, ...)  become separators of their own to be disruptive, leading to subtle and hard to track problems.  

Regards

Pascal

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