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Re: Guile initialization and string evaluation with C++

From: Nala Ginrut
Subject: Re: Guile initialization and string evaluation with C++
Date: Thu, 27 Mar 2014 19:39:17 +0800

On Mon, 2014-03-24 at 12:08 -0700, Eduardo Acuña wrote:
> Hello everybody.
> lately i have been programming in scheme, but i'm usually obligated to use
> C++ for school.
> So i try to use guile inside C++ programs.
> I wrote two little classes for simplifying the initialization of guile and
> evaluating expressions, and i have a couple of questions regarding how can
> i enhance the implementation.
> The two classes are:
> - GuileApplication (does the scm_boot_guile and other stuff)
> - GuileEvaluator (has an eval function that gets a expression as an
> std::string and returns the result as an std::string)

Please write Makefile and use pkg-config next time ;-)
And it's better if you can use github or similar thing we can read the
code directly. Not all guys want to download a strange zip file from a
strange link.

> Questions about the GuileApplication class:
> 1.- How can a send scm_boot_guile a member function? (relevant functions
> are init, initializationHack and guileMain)
> [Explanation: the scm_boot_guile is called from a member function of
> GuileApplication and i want to send another member function as the
> "inner_main", my half-solution was to use a normal function that received a
> GuileApplication* casted as a void* and dereferencing that to call the
> other member function (i had to friend this function and pass the instance
> as the void * data )]

Can you explain why you want to `send' scm_boot_guile'? I can't figure
it out from your description and your code.

> 2.- Is the "(use-modules (system repl server)) (spawn-server)" a good way
> of getting access to the program with emacs and geiser's
> 'connect-to-guile'? (relevant functions are guileMain)
> [Explanation: i like to use an external repl to test functions with emacs
> and geiser, the only way i know to make this happen is to eval those two
> expressions, but i don't know if it is the right way to do it]

I don't know if it's the best way, but the same method appears in
geiser's code. So I think it's not bad for you.

> Questions about the GuileEvaluator class:
> 3.- How can i handle better the possible errors from evaluating expressions
> from C++? (relevant functions are evalString, guileEvalHandler,
> handler_message, guileEvalBody)
> [Explanation: i think the curren way i'm handling errors is a bit clumsy, i
> wanted to show the error message but don't exit the entire program, so i
> had to copy the handler_message from the guile source, but i'm sure there
> is a better way of doing this]

I'm not sure what you mean. If you don't want to exit while exceptions
occur, you can just catch them all with #t and print the error message,
then call your main loop again.
My solution is not a good one, just one of the possible way, maybe not
suit for your code. I suggest you elaborate your problem.

> 4.- How can i avoid having to close the output string port and creating a
> new one each time i convert an SCM value to an std::string? (relevant
> functions are scmToString)
> [Explanation: i want the output string port to be cleared when i evaluate
> an expression and return the result as an std::string]

Your scmToString is too complicated for its function I understand.
Maybe you just need scm_object_to_string

BTW, your program is cool ;-)

> I attached the code i'm working on, i hope you can point me in the right
> direction.
> I will appreciate any suggestion regarding this program :-)
> By the way, i'm currently trying to use guile in a couple of games with the
> SFML library, and with this thow classes i wrote a very simple demo to
> start working from, if you would like to check it out here it is:
> Eduardo.

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