Subj : Re: The root of the syntax tree
To   : netscape.public.mozilla.jseng
From : joao
Date : Wed Jul 07 2004 10:29 pm

Brendan Eich wrote:
> Actually, I recall my design decision now.  PN_NULLARY is accurate, 
> there are no JSParseNode kids of a TOK_STRING (or of a TOK_OBJECT). 
> PN_NAME, on the other hand, denotes a TOK_NAME or TOK_DOT node, which 
> may or must (respectively) have a non-null pn_expr "child".  Because 
> this pn_expr link may be null, and because of the other distinct members 
> of the pn_u.name variant such as atom, I made another "arity" than 
> PN_UNARY to distinguish TOK_NAME, TOK_DOT, and any similar future types.

Yes, I get it.

> So you should not take PN_NULLARY to mean "not a literal".  Arity has to 
> do with tree node child count, and a literal string or object is always 
> a leaf node: zero kids.  That does not mean it can't have ad-hoc leaf 
> data, e.g., pn_atom.

Well, looking at the source code (jsparse.h), the question is how do I 
access the sub-fields inside the union... actually, *which* sub-fields 
do I access is a better question. Looking at the definition of 
JSParseNodeArity, just before the definition of JSParseNode, there seems 
to be a mapping between those enum values and the sub-fields, so the 
reader is led to believe that if it's a PN_NAME, then you can access 
pn_atom, otherwise you can't. And if it's PN_NULLARY, then there's 
nothing else (dval maybe ?).

But you were right, it *is* described in the comment, if you read it 
carefully. I'll be using that.

> /be

Joao

-- 
joao at teaser dot fr

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