Wow, thanks for the detailed explanation. That is really interesting! Norbert
Am 20.05.2013 um 17:57 schrieb Marcus Denker <marcus.den...@inria.fr>: > > On May 20, 2013, at 4:44 PM, Paul Davidowitz <pdavi...@fastmail.fm> wrote: > >> I just started following this Dev mailing list, and I saw that 'AST >> Everywhere' and 'Reflectivity' were mentioned as very promising (I >> already know about Slots). >> Can someone in a nutshell please describe these developments? Thanks, > > > Right now, the compiler uses it's own AST, Syntax highlighting uses a very > minimal > token stream (and it's own parser), the refactoring engine has one, too. > And then there is Bytecode which is used by the Debugger, for example. > > As a first step we plan to use the Refactoring AST for everything > (Compiler, Refactoring, Syntax highlighting ) > > There is a AST Interpreter useful for experimenting, maybe in the future the > debugger can use this instead of relying on byte code. (but this is for far > later). > > Now with the AST already there, all the tools can rely on it (Gisela Decuzzi > is working on this:) > > Navigation. When selecting code or navigating expressions, the editor can do > better then just using word boundaries: > > http://www.youtube.com/watch?feature=player_embedded&v=pFLyzEI0jmE > > Suggestions. When we want to do an actions on a selection, why not just show > those that make sense? > Why do I need to carefully highlight a selector to browser implementors? The > AST model can do much better! > > http://www.youtube.com/watch?feature=player_embedded&v=WmNKbewOXkE > > Reflectivity > ========= > > Behavioral Reflection is quite interesting.. but there is not that much in > Smalltalk by default to deeply hook > into how code is executed. > > There are MethodWrappers (to be loaded as an additional tool). There is an > in-image Bytecode Interpreter > (hidden in ContextPart). > > People started to want more. "In this class, all Ivar accesses should be > treated differently". Things like that. > > So people tried to improve Smalltalk in the past. E.g. adding a CLOS Style > MOP (Noury did that with MetaClassTalk). > But it is difficult to do it in a way that it does not get very slow (not > introduce an overhead for every operation). > > And in the end, the MetaClass style MOP is quite limiting: All change of > semantic is done *per Class*. Already > quite nice, but limiting... > > So in 2003 Eric Tanter finished his PhD and he invented this: > > Eric Tanter , Jacques Noye , Denis Caromel , Pierre Cointe: > Partial Behavioral Reflection: Spatial and Temporal Selection of Reification > http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.58.8141 > > And as fate wanted, he was visiting in Bern the week before Christmas 2004, > which gave me enough > time to implement a Bytecode Transformation thing in the style of Javassist > that this stuff was using. > But it was cumbersome… so at some point I thought "Bytecode Sucks", and took > the Reflex model but > transported it on the AST Level. > http://scg.unibe.ch/archive/phd/denker-phd.pdf > > So… what this means is that the AST can be annotated with so-called "meta > links". When you set a link, > the system behind the scene makes sure that new code is generated on the next > call. > > One way to think about this is that these links are just extremely > generalized break-points. So you can > set a link that says "before this node, send #halt to Halt". > But they are much more powerful: > -> selector > -> metaObject > -> what to pass as parameters > -> a condition > -> is it #before, #after, #around? > > can be set as wanted. > > So after some thinking one realizes that this subsumes > -> BreakPoints > -> MethodWrappers > -> CLOS style MOP where the class is the meta object > -> AOP style crosscutting. (Aspects is just a pattern on top) > -> …. > > e.g. Code Coverage: > ------------------------------ > > - add a #markExecuted to RBProgramNode. > - install this link an all the nodes that you are interested in: > > link := GPLink new metaObject: #node; selector: #markExecuted. > (markExecuted can even deinstall the link) > > CLOS style MOP > ---------------------- > (for sends:) > > link := GPLink new > metaObject: #class; > selector: #send:to:with:; > arguments: #(selector receiver arguments) > control: #instead. > > Add this link to all send nodes in your class after the compiler compiles > something, and > your class hierarchy has a CLOS style where every send is indirected through > a method > in the class side. > > Javassist (or Bytesurgeon) style "execute this code before this operation" > ------------------------ > > link := GPLink new > metaObject: [:object | object color = Color red ifTrue: [Beeper beep]]; > selector: #value:; >  arguments: #(object). > > The nice thing is that these links are highly dynamic: they can be installed > quickly, remove > themselves, propagate themselves over the AST at runtime even. > > Marcus
