Re: implementing eval command

Re: implementing eval command

[Michael Snyder]

Moving this to "gdb" list, since it is not a patch.

On Thu, 2008-02-14 at 18:18 +0200, Yakov Lerner wrote:
> I'd like to make a patch that implements eval command, as follows.
> I have following idea to implement eval simply:
> Syntax of eval will be similar to the syntax of 'printf' command:
>          eval "string with %..." comma-separated-expressions
> Implementation relies on existing printf_command() function,
> by rewriting printf_command into pair of functions, one that computes
> result of printf as allocated string; both printf_command and eval_command
> will use compute_printf() function.
> What do you think ?

Hmmm, that would be one way of getting around the 
limitations of some commands that can't accept expressions
as arguments (mentioned in another thread).

What do you see as the context for this eval command?
How do you imagine it will be used?

Re: implementing eval command

[Yakov Lerner]

On Fri, Feb 15, 2008 at 7:58 PM, Michael Snyder <msnyder@specifix.com> wrote:
> Moving this to "gdb" list, since it is not a patch.
>
>
>
>  On Thu, 2008-02-14 at 18:18 +0200, Yakov Lerner wrote:
>  > I'd like to make a patch that implements eval command, as follows.
>  > I have following idea to implement eval simply:
>  > Syntax of eval will be similar to the syntax of 'printf' command:
>  >          eval "string with %..." comma-separated-expressions
>  > Implementation relies on existing printf_command() function,
>  > by rewriting printf_command into pair of functions, one that computes
>  > result of printf as allocated string; both printf_command and eval_command
>  > will use compute_printf() function.
>  > What do you think ?
>
>  Hmmm, that would be one way of getting around the
>  limitations of some commands that can't accept expressions
>  as arguments (mentioned in another thread).
>
>  What do you see as the context for this eval command?
>  How do you imagine it will be used?

Apparently, the capability to insert variable into arbitrary part of
gdb command is missing in gdb. I hit this several days ago when I needed
to make a script that uses 'thread apply $num where' to a subset of threads
in a program that had hundreds of threads and I was told on the list that this
is impossible.

I also see other requests for eval command on the mailing list archive.
So, instead of enriching just 'thread apply' command to accept variable
(or maybe parenthesized expression) I thought it's much more generic
to have eval command in the end.

I thought about easy way to implement it, and then I got idea of using
the print-like format and comma-separated arg list.

Yakov

Re: implementing eval command

[Michael Snyder]

On Sat, 2008-02-16 at 09:36 +0200, Yakov Lerner wrote:
> On Fri, Feb 15, 2008 at 7:58 PM, Michael Snyder <msnyder@specifix.com> wrote:
> > Moving this to "gdb" list, since it is not a patch.
> >
> >
> >
> >  On Thu, 2008-02-14 at 18:18 +0200, Yakov Lerner wrote:
> >  > I'd like to make a patch that implements eval command, as follows.
> >  > I have following idea to implement eval simply:
> >  > Syntax of eval will be similar to the syntax of 'printf' command:
> >  >          eval "string with %..." comma-separated-expressions
> >  > Implementation relies on existing printf_command() function,
> >  > by rewriting printf_command into pair of functions, one that computes
> >  > result of printf as allocated string; both printf_command and eval_command
> >  > will use compute_printf() function.
> >  > What do you think ?
> >
> >  Hmmm, that would be one way of getting around the
> >  limitations of some commands that can't accept expressions
> >  as arguments (mentioned in another thread).
> >
> >  What do you see as the context for this eval command?
> >  How do you imagine it will be used?
> 
> Apparently, the capability to insert variable into arbitrary part of
> gdb command is missing in gdb. I hit this several days ago when I needed
> to make a script that uses 'thread apply $num where' to a subset of threads
> in a program that had hundreds of threads and I was told on the list that this
> is impossible.

Oh yes, that was the thread I was thinking about.

> I also see other requests for eval command on the mailing list archive.
> So, instead of enriching just 'thread apply' command to accept variable
> (or maybe parenthesized expression) I thought it's much more generic
> to have eval command in the end.
> 
> I thought about easy way to implement it, and then I got idea of using
> the print-like format and comma-separated arg list.

Cool, well, personally I think this is a very interesting idea.
With the printf format, it should be possible to construct
fairly complex commands.