New front end, help needed

New front end, help needed

[James Buchanan]

Hi everyone,

I suppose the thing that stumps me is the trees.  I have
looked in tree.def, tree.h, coretypes.h and many other places
without much success.  Sometimes it appears to be a union
(coretypes.h - but just a nothing typedef saying tree is a
pointer to union treenode) but sometimes it appears to be a
struct.  I can't see what it is supposed to be.  If I could make
these trees for arithmetic expressions, assignment
statements, functions, and so on, then I could compile a
new language by writing a front end.  But I don't even know
where to start.

By the way, my new language is a dialect and subset of BASIC.
Hopefully not so useless that it's useless, but useful enough
to learn a lot about writing a front end, so I can implement
something more ambitious. :-)

Do you have any tips for me?  I see that everything gets a tree,
even single numbers that appear as constants in an expression.
So to compile up the following BASIC:

DECLARE name$, amount%, tax%

INPUT "Enter your name: ", name$
PRINT "Hello ", name$

INPUT "Enter an amount: ", amount%

tax% = amount% - (amount% * 0.05)

IF tax% < 100.0 THEN
    PRINT "You didn't pay much tax!"
ELSE
    PRINT "I feel sorry for you."
END IF

PRINT "You paid $", tax%, " in taxes."

.... I would need to write the parser which calls
on the tree functions and macros to build things up.

Now, for something like:

DECLARE name$, amount%, tax%

... where $ and % mean "string type" and "real type"
respectively, I could go:

tree str_decl = build_decl(STRING_DECL, get_identifier(name), type);

... where I have defined STRING_DECL, or I use a POINTER_DECL
or something else as in tree.def.

Now, after this, what next?  I suppose it is all taken care of by GCC...
and assembler comes out and gets processed and linked.

Suppose I need a string, use an ARRAY_DECL (as in an array
of chars or unicode wchar's) or a POINTER_DECL?  I suppose
I don't use POINTER_DECL, since there is no actual object,
only a placeholder address for something else, so I use an
ARRAY_DECL or something to internally represent var$ as
a C string.

Where to from here?  I need to grow strings automagically
within the compiler, and handle IF var$ = foo$ THEN... by
calling strcmp() or something like that, within the runtime
library.  How do I implement these operators?  How do I
get the assembler that is generated to hook into the
runtime code needed?

Sorry for all this, but I am not sure who to ask or where
to look or anything like that.

Kind regards,
James

Re: New front end, help needed

[Daniel Jacobowitz]

On Wed, Jan 01, 2003 at 03:14:47AM +1100, James Buchanan wrote:
> Hi everyone,
> 
> I suppose the thing that stumps me is the trees.  I have
> looked in tree.def, tree.h, coretypes.h and many other places
> without much success.  Sometimes it appears to be a union
> (coretypes.h - but just a nothing typedef saying tree is a
> pointer to union treenode) but sometimes it appears to be a
> struct.  I can't see what it is supposed to be.  If I could make
> these trees for arithmetic expressions, assignment
> statements, functions, and so on, then I could compile a
> new language by writing a front end.  But I don't even know
> where to start.

> Suppose I need a string, use an ARRAY_DECL (as in an array
> of chars or unicode wchar's) or a POINTER_DECL?  I suppose
> I don't use POINTER_DECL, since there is no actual object,
> only a placeholder address for something else, so I use an
> ARRAY_DECL or something to internally represent var$ as
> a C string.
> 
> Where to from here?  I need to grow strings automagically
> within the compiler, and handle IF var$ = foo$ THEN... by
> calling strcmp() or something like that, within the runtime
> library.  How do I implement these operators?  How do I
> get the assembler that is generated to hook into the
> runtime code needed?
> 
> Sorry for all this, but I am not sure who to ask or where
> to look or anything like that.

You should take a good look at "treelang", which is the sample
frontend, and also a good look at the GCC Internals manual (gccint.info
in gcc/doc/ in a built tree).

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer

Re: New front end, help needed

[James Buchanan]

At 11:22 AM 12/31/2002 -0500, Daniel Jacobowitz wrote:
>You should take a good look at "treelang", which is the sample
>frontend, and also a good look at the GCC Internals manual (gccint.info
>in gcc/doc/ in a built tree).

Thanks for this.  I can get the gccint manual on the website,
I just went and had a look.

I've already seen treelang, but it wasn't very helpful for me.  I was
looking for more of something that starts from the very beginning.
It already requires a good knowledge of GCC internals because
I can't fully understand it.  I suppose I need to fill in the gaps myself
and keep going back for another look until it falls into place. :-)

Cheers
James