BASIC advice wanted.

[Malcolm]

After some days' hard work I am now the proud possessor of an ANSI C BASIC
interpreter.

The question is, how is it most useful?

At the moment I have a function

int basic(const char *script, FILE *in, FILE *out, FILE *err);

It returns 0 on success or -1 on fail.
and I'm calling it with stdin, stdout and stderr (err is for reporting
errors in the script, not for user errors).

This is fine for test purposes, but realistically it is not going to be
useful for anything beyond teaching newbies how to program in BASIC.

The main motive is to use the BASIC interpreter as a component of editors.
The idea is that a game designer can write a little BASIC program, maybe to
control the diffusion pattern of smoke particles, or maybe for some
AI-related stuff. Since the script is interpreted there is no reason to
recompile.

However setting up temporary files to pass data in and out of the BASIC
seems clumsy. There is also no way in C to specify a "user" FILE *,
something that pops up a Window to get input, for example.

I'm also not happy with the BASIC INPUT statement, it's fine for stdin, but
not so good for reading values from a typical formatted text file. However I
don't want to stray too far from core BASIC, or else the user will have to
learn a new programming language to use the program.

 

[Peter Pichler]

After some days' hard work I am now the proud possessor of an ANSI C BASIC
interpreter.

I doubt it. How do you deal with things like PEEK, POKE, PLOT and all the
other graphics or sound commands in ANSI C?

The question is, how is it most useful?

No, the question is, what is your C question? ;-)

Peter

 

[Joona I Palaste]

I doubt it. How do you deal with things like PEEK, POKE, PLOT and all the
other graphics or sound commands in ANSI C?

Perhaps his interpreter interprets a BASIC version which doesn't have
them? ANSI BASIC is incredibly small. It's even smaller than C=64 BASIC
V2.

 

[Peter Pichler]

ANSI BASIC is incredibly small.

ANSI BASIC? One learns something new every day!

 

[Joona I Palaste]

ANSI BASIC? One learns something new every day!

Yes. I didn't know about it either until Dan Pop told me. Apparently
it's even missing the IF... THEN structure. The only thing ANSI BASIC
can do in an IF statement is a GOTO. Several other BASIC dialects allow
calling other statements too.
(Though I would be surprised if this was valid BASIC

10 FOR I=1 TO 10
20 IF I<9 THEN NEXT I

--
/-- Joona Palaste ([email protected]) ------------- Finland --------\
\-- http://www.helsinki.fi/~palaste --------------------- rules! --------/
"As a boy, I often dreamed of being a baseball, but now we must go forward, not
backward, upward, not forward, and always whirling, whirling towards freedom!"
- Kang

 

[Joona I Palaste]

Yes. I didn't know about it either until Dan Pop told me. Apparently
it's even missing the IF... THEN structure. The only thing ANSI BASIC
can do in an IF statement is a GOTO. Several other BASIC dialects allow
calling other statements too.
(Though I would be surprised if this was valid BASIC

10 FOR I=1 TO 10
20 IF I<9 THEN NEXT I

Well, C=64 BASIC V2 seems to accept it... it's treating "NEXT I" as
"increment I and go back to the FOR command". So therefore the above
is equivalent to:

10 FOR I=1 TO 10
20 IF NOT(I<9) THEN END
30 NEXT I

 

[Malcolm]

I doubt it. How do you deal with things like PEEK, POKE, PLOT
and all the other graphics or sound commands in ANSI C?

It's a cut down BASIC without any hardware-specific commands.

No, the question is, what is your C question? ;-)

That's the C question. Given that I've got a BASIC interpreter, what is the
most useful interface to the rest of the C program that calls it?

 

[Joona I Palaste]

That's the C question. Given that I've got a BASIC interpreter, what is the
most useful interface to the rest of the C program that calls it?

Your BASIC interpreter is written in ANSI C, but is your program around
it also written in ANSI C? If not, then you can use a non-standard "pipe
stream" and pass it as an argument to your interpreting function. That
way you can send data between your outer program and your interpreter
efficiently.

 

[Nils Petter Vaskinn]

Malcolm <[email protected]> scribbled the following:

Your BASIC interpreter is written in ANSI C, but is your program around
it also written in ANSI C? If not, then you can use a non-standard "pipe
stream" and pass it as an argument to your interpreting function. That
way you can send data between your outer program and your interpreter
efficiently.

How about callback functions? Something like:

typedef int (*input_handler)(char**);
typedef int (*output_handler)(const char*);
typedef int (*error_handler)(int,int,char*); /* errno, line, text */

int basic(const char *script,
input_handler ih,
output_handler oh,
error_handler eh);

Giving the calling program the opportunity to define functions to deal
with input, output or errors. These programs may then write to file or
process the error or do whatever they feel like.

(And you can provide handler functions that writes to files if that's
what the user wants them to do.)

 

[Joona I Palaste]

How about callback functions? Something like:

typedef int (*input_handler)(char**);
typedef int (*output_handler)(const char*);
typedef int (*error_handler)(int,int,char*); /* errno, line, text */

int basic(const char *script,
input_handler ih,
output_handler oh,
error_handler eh);

Giving the calling program the opportunity to define functions to deal
with input, output or errors. These programs may then write to file or
process the error or do whatever they feel like.

(And you can provide handler functions that writes to files if that's
what the user wants them to do.)

I think this design is good. If this were Java, I'd design the BASIC
interpreter so that I/O is handled by calling interfaces, one called
Input, the other called Output. Implementors of the outside system
would have to implement these interfaces and pass the implementations
as parameters to the interpreter object.