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From: David Abrahams (david.abrahams_at_[hidden])
Date: 2002-01-15 11:51:07

----- Original Message -----
From: "Vladimir Prus" <ghost_at_[hidden]>
> Them, why you say:
> "In other words, we
> choose the shortest path from sources to targets"
> Do you implicitly assume that the transformation chain will contain only
> source, one target) rules?

No, I just shouldn't have said it.

> > Take the example where we don't have DLP->CPP, but DLP->LEX->CPP, so we
> > have a path-length mismatch. I claim we want the search graph to look
> > a straight line for each source file, so we need to use sets of target
> > types (I don't mean to suggest this must be a BFS):
> >
> > WD -> {DLP,WHL} -> {LEX,CPP} -> {CPP,OBJ} -> {OBJ,OBJ}
> >
> > We need sets of source files because something has to know that they are
> > kept together
> Looks so, indeed.
> > This would be easy if we searched from source to target. I am reluctant
> > do that, however, because even though there are many generators of OBJ
> > products, I fear that many more might be able to match a source type,
> > TEXT.
> A! Actually, I was always considereing search from sources! I though
> in the opposite direction was an idea you only recently got.

I don't remember how it happened. I do think starting with sources is more
natural in many ways.

> > Ah! I remember what I thought about this: it might not be so bad to ask
> > people to write something like this for these cases:
> >
> > exe foo : @asm ;
> > wd asm : asm.wd ;
> >
> > This is an easy way out.
> This is an easy way out, but... wouldn't it require wd rule to be ad-hoc
> i.e. wouldn't it simple create conversion sequence explicitly, again
> bypassing the general scheme?

No, sorry, I wasn't clear. The product of wd is .cpp files. Not ad-hoc at
in fact, if you wanted just the lexer .cpp product from wd, you might write:

exe foo : @asm.lex

> > In other words, not everything needs to use the fancy search mechanism.
> Okay, I'm guilty of overgeneralization :-)

A deadly sin ;-)

> > Let me know what you think about taking the easy way out. Please also
> > consider the bottom-up BFS. For most source types, there are only a few
> > transformations.
> Okay, I'll post futher opinions as soon as they're ready. Meanwhile, it
> that we've agreed on all the other matters.



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