Re: [proto] Manipulating an expression tree
On Wed, Apr 6, 2011 at 10:29 PM, Karsten Ahnert
karsten.ahn...@ambrosys.de wrote:
Is there a direct way to transform an expression tree into another one?
For example, is it possible that every proto::plus node is
transformed to it left child? I tried to solve this problem via protos
build-in transforms without success. It seems that they are suited for
evaluation of an existing tree, but I might be wrong.
Hi Karsten,
I'm pretty sure they can do both. For your example, I think something
along the lines of this might work (untested):
struct LeftPlus :
boost::proto::or_
boost::proto::terminalboost::proto::_,
boost::proto::when
boost::proto::plusboost::proto::_, boost::proto::_,
LeftPlus(boost::proto::_left)
,
boost::proto::nary_expr boost::proto::_, boost::proto::varargLeftPlus
{};
This should recurse through expressions and replace sequences of
pluses with the left-most terminal. You may need some other criteria
to end the recursion depending on your use case.
Disclaimer: I'm relatively new to proto myself, so the experts might
have better solutions!
Cheers,
--
Bart
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Re: [proto] Manipulating an expression tree
Great! It works perfectly, alltough I don't understand the code
completely yet.
Another question is: can a node have a state. In my algorithm it would
be nice, if every proto::multiplies node stores some intermediate
values which are used during later evaluations of the tree.
Thanks,
Karsten
On 04/06/2011 10:53 PM, Bart Janssens wrote:
On Wed, Apr 6, 2011 at 10:29 PM, Karsten Ahnert
karsten.ahn...@ambrosys.de wrote:
Is there a direct way to transform an expression tree into another one?
For example, is it possible that every proto::plus node is
transformed to it left child? I tried to solve this problem via protos
build-in transforms without success. It seems that they are suited for
evaluation of an existing tree, but I might be wrong.
Hi Karsten,
I'm pretty sure they can do both. For your example, I think something
along the lines of this might work (untested):
struct LeftPlus :
boost::proto::or_
boost::proto::terminalboost::proto::_,
boost::proto::when
boost::proto::plusboost::proto::_, boost::proto::_,
LeftPlus(boost::proto::_left)
,
boost::proto::nary_expr boost::proto::_, boost::proto::varargLeftPlus
{};
This should recurse through expressions and replace sequences of
pluses with the left-most terminal. You may need some other criteria
to end the recursion depending on your use case.
Disclaimer: I'm relatively new to proto myself, so the experts might
have better solutions!
Cheers,
--
Dr. Karsten Ahnert
Ambrosys GmbH - Gesellschaft für Management komplexer Systeme
Geschwister-Scholl-Str. 63a
D-14471 Potsdam
Tel: +4917682001688
Fax: +493319791300
Ambrosys GmbH - Gesellschaft für Management komplexer Systems
Gesellschaft mit beschränkter Haftung
Sitz der Gesellschaft: Geschwister-Scholl-Str. 63a, 14471 Potsdam
Registergericht: Amtsgericht Potsdam, HRB 21228 P
Geschäftsführer: Dr. Karsten Ahnert, Dr. Markus Abel
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Re: [proto] Manipulating an expression tree
(Please don't top-post. Rearranging...)
On 4/7/2011 5:45 AM, Karsten Ahnert wrote:
On 04/06/2011 10:53 PM, Bart Janssens wrote:
On Wed, Apr 6, 2011 at 10:29 PM, Karsten Ahnert
karsten.ahn...@ambrosys.de wrote:
Is there a direct way to transform an expression tree into another one?
For example, is it possible that every proto::plus node is
transformed to it left child? I tried to solve this problem via protos
build-in transforms without success. It seems that they are suited for
evaluation of an existing tree, but I might be wrong.
Hi Karsten,
I'm pretty sure they can do both. For your example, I think something
along the lines of this might work (untested):
struct LeftPlus :
boost::proto::or_
boost::proto::terminalboost::proto::_,
boost::proto::when
boost::proto::plusboost::proto::_, boost::proto::_,
LeftPlus(boost::proto::_left)
,
boost::proto::nary_expr boost::proto::_, boost::proto::varargLeftPlus
{};
This should recurse through expressions and replace sequences of
pluses with the left-most terminal. You may need some other criteria
to end the recursion depending on your use case.
Disclaimer: I'm relatively new to proto myself, so the experts might
have better solutions!
Cheers,
Great! It works perfectly, alltough I don't understand the code
completely yet.
It takes time, but it'll be worth it. You can't do much with Proto with
grokking grammars and transforms.
Another question is: can a node have a state. In my algorithm it would
be nice, if every proto::multiplies node stores some intermediate
values which are used during later evaluations of the tree.
No. Intermediate expression nodes carry no run-time state in their
nodes. They only carry compile-time information in the form of the tag.
That's how a plus node is distinguished from a minus node, for instance.
If you need to compute intermediate values, you can use a transform to
build a parallel structure.
--
Eric Niebler
BoostPro Computing
http://www.boostpro.com
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