On Saturday, 7 July 2012 at 18:55:57 UTC, Chad J wrote:
I was thinking the same thing.
My intent is to create a kind of regular-expression-of-nodes
with push/pop operators to recognize ascent and descent on the
tree. Such a regular expression would allow one to capture
subtrees out of generalized patterns and then place them into
new trees that then become the input for the next pattern or
set of patterns. I think this is much closer to how I
conceptualize semantic analysis than how semantic analysis is
done in front ends like DMD: it should to be done with pattern
recognition and substitution, not with myriad nested
if-statements and while-loops.
Funny, we've discussed an idea to introduce some hybrid of regex
and xpath for querying, searching and traversing AST with Dmitry
a few weeks ago. A custom NDepend-like Code Query Language was
the major alternative we considered. Discussion started on this
forum and continued via email.
In this vision I do not use classes and inheritance for my AST.
Instead I use structs that contain some kind of nodeType
member that would be one of the tokens/symbols in the grammar,
like TOK_WHILE_NODE in the above code. Dynamic dispatch is
instead performed by (very fast) DFAs recognizing parts of the
AST.
Exactly. This idea first came to me in April after I implemented
the first top-down recursive descent custom parser for a D
subset. I tried Visitor pattern before that and wasn't happy.
There are some subtle difficulties which I believe will be
possible to overcome, most important being the need to introduce
a mechanism for hierarchical classification (like a pow
expression being an assign expression at the same time).
