Re: multiline comments

[David Bateman]

John W. Eaton wrote:

> On 15-Apr-2005, Quentin Spencer <address@hidden> wrote:
>
> | I'm not sure if this is what was meant in the original question, but 
> | Matlab 7 now supports block comments of the form
> | %{
> |    commented stuff here
> | %}
> | 
> | As far as I know this has not yet been implemented in octave.
>
> Right.  Well, it is a relatively new addition.
>
> | It may be 
> | implemented eventually, but I think it's a low priority for those most 
> | actively involved in octave development. I'm sure John would welcome a 
> | patch to support this.
>
> Sure, it should not be too hard.  Most of the changes would be in
> src/lex.l.  Some possible complications are
>
>  * Do these comments nest?  Do you get this behavior:
>
>      %{ 1
>      %{ 2
>      %} matches 2
>      %} matches 1
>
>   or
>
>      %{ 1
>      %{ 2
>      %} matches 1
>      %} error, warning, or just ignored (it is a valid comment)
>
>  


Running the function

function nest ()
 %{
 disp("1");
 %{
 disp("2");
 %}
 disp("3");
 %}
end

on matlab v7sp2 displays nothing, so the first case is the way matlab 
implements it, and this makes more sense, as you can comment a large 
part of already commented code.

>  * You must save the text of these comments as you read them, so that
>    they can be printed by the parse tree printing code, and you must
>    modify the printing code to properly emit the saved comments.
>
>  * You must maintain the line and column number information recorded
>    by the lexer when you read the comments.
>
> | Unfortunately I'm not familiar enough with  
> | octave's parser to attempt this. In the mean time, as Geordie suggests, 
> | there are other workaraounds (my preferred one is if(0) ... end).
>
> Yes, if(0) endif is the more common way of faking block comments.  The
> disadvantage is that the text inside the if(0) endif block must be
> valid code.  In a block comment, you could have anything except "%}"
> at the beginning of a line.
>
> jwe
>
>
>
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>  



--
David Bateman                                address@hidden
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