Re: [Pharo-project] Hints and clues for a Pharo newb
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Re: [Pharo-project] Hints and clues for a Pharo newb
 
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On Wed, Apr 21, 2010 at 4:34 PM, Hernán Morales Durand <[hidden email]> wrote: 2010/4/21 Lukas Renggli <[hidden email]>: Right. In other Smalltalks aBlockContext is the resulting context of a block and it is now with the closure compiler. Or rather a new context is created when a BlockClosure is sent the value message. The context is an instance of methodContext though.
In Squeak (or the old compiler) block contexts were created using Yes. But MethodContext behaves differently depending on whether its closureOrNil inst var is nil (a normal method) or a BlockClosure (an activation of a block). If nil, ^-returns return to the context's sender. If not nil ^-returns return from the home context, found by following the outerContext chain through the closureOrNil inst var. So we no longer need BlockContext.
This also means we only need one context class, and some time I'd like to merge the two ContextPart and MethodContext classes into a single Context class. Possibly the name should be ExecutionContext or MethodOrBlockContext or? Suggestions?
It depends on whether the expression is executed at method level or at block level. As a test this should be: testIsExecutingBlock self assert: ([: arg | arg perform: #isExecutingBlock ] value: thisContext) == false. [self assert: ([: arg | arg perform: #isExecutingBlock ] value: thisContext) == true] value
Can somebody justify the result? isExecutingBlock answers if the receiver is executing a block or not. It does not answer whether the context in which isExecutingBlock is sent is executing a block or not. Remember that
[:arg| arg == thisContext] value: thisContext is false. thisContext is rebound within every actual method or block scope. HTH Eliot
But its not a property of Pharo. It is a property of the VM. In Cog contexts are not actual objects all the time, only when needed. And Cog runs Pharo images just as it runs Squeak images. So it would be incorrect to say "in Pharo" and better to say "in the standard Squeak VM".
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Re: [Pharo-project] Hints and clues for a Pharo newb
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On 2010-04-21, at 5:04 PM, Eliot Miranda <[hidden email]> wrote: > This also means we only need one context class, and some time I'd like to merge the two ContextPart and MethodContext classes into a single Context class. Possibly the name should be ExecutionContext or MethodOrBlockContext or? Suggestions? I suggest ActivationContext. Colin |
Re: [Pharo-project] Hints and clues for a Pharo newb
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In reply to this post by Eliot Miranda-2
> Yes. But MethodContext behaves differently depending on whether its closureOrNil inst var is nil (a normal method) or a BlockClosure (an activation of a block). If nil, ^-returns return to the context's sender. If not nil ^-returns return from the home context, found by following the outerContext chain through the closureOrNil inst var. So we no longer need BlockContext. Hi Elliot I was wondering why you do not use two classes and you do the nil check? > This also means we only need one context class, and some time I'd like to merge the two ContextPart and MethodContext classes into a single Context class. Possibly the name should be ExecutionContext or MethodOrBlockContext or? Suggestions? > > > Now, test yourself before evaluating :) what should be the result of > this expression? > > [: arg | arg perform: #isExecutingBlock ] value: thisContext > > It depends on whether the expression is executed at method level or at block level. As a test this should be: > > testIsExecutingBlock > self assert: ([: arg | arg perform: #isExecutingBlock ] value: thisContext) == false. > [self assert: ([: arg | arg perform: #isExecutingBlock ] value: thisContext) == true] value > > Can somebody justify the result? > > isExecutingBlock answers if the receiver is executing a block or not. It does not answer whether the context in which isExecutingBlock is sent is executing a block or not. Remember that > > [:arg| arg == thisContext] value: thisContext > > is false. thisContext is rebound within every actual method or block scope. > > HTH > > Eliot > > > >> Context creation is optimized in the VM in most Smalltalks, so it's > >> only really created as an object in the environment (reified) when > >> it's specifically needed through "thisContext". > > > > In Pharo contexts are not reified like that. Stack-frames are actual > > objects at all times. However, for speed reasons, their creation and > > garbage-collection is optimized by the VM. Stack frames get > > automatically recycled if nobody refers to them. > > > > I think is what I said :) > > But its not a property of Pharo. It is a property of the VM. In Cog contexts are not actual objects all the time, only when needed. And Cog runs Pharo images just as it runs Squeak images. So it would be incorrect to say "in Pharo" and better to say "in the standard Squeak VM". > > > >> There are several applications related with computational reflection > >> (Reflective Programming, Meta-Programming, MOP, etc) which makes use > >> of the current context. > > > > Also: exception handling, generators, continuations, co-routines, ... > > > > For another fun use of "thisContext" check this Stack-Overflow question: > > > > http://stackoverflow.com/questions/2500483/is-there-a-way-in-a-message-only-language-to-define-a-whiletrue-message-without-r > > > > Lukas > > > > -- > > Lukas Renggli > > www.lukas-renggli.ch > > > > _______________________________________________ > > Pharo-project mailing list > > [hidden email] > > http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project > > > > _______________________________________________ > Pharo-project mailing list > [hidden email] > http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project > |
Re: [Pharo-project] Hints and clues for a Pharo newb
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In reply to this post by Colin Putney
Yes this is a nice name On Apr 22, 2010, at 6:06 AM, Colin Putney wrote: > > > On 2010-04-21, at 5:04 PM, Eliot Miranda <[hidden email]> wrote: > >> This also means we only need one context class, and some time I'd like to merge the two ContextPart and MethodContext classes into a single Context class. Possibly the name should be ExecutionContext or MethodOrBlockContext or? Suggestions? > > I suggest ActivationContext. > > Colin > |
Re: [Pharo-project] Hints and clues for a Pharo newb
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In reply to this post by stephane ducasse-2
On Thu, Apr 22, 2010 at 12:49 AM, stephane ducasse <[hidden email]> wrote:
One reason is backward compatibility. The existing VM ensures that closureOrNil (which used to be called receiverMap) is nil. The other is the internal workings of the VM. The nil test is done by the VM on every ^-return. The VM isn't going to waste time sending a message. It is going to do a nil test.
In fact in Cog the VM doesn't even do a nil test since in machine code the JIT knows at compile time whether an ^-return is within a block or not, and in the stack interpreter whether a frame is a block activation is indicated by a status bit in the method field of a frame.
So don't think Smalltalk code, think optimized VM internals. We're not going to waste time instantiating some object just to tag a structure as not being a block activation. HTH Eliot
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Re: [Pharo-project] Hints and clues for a Pharo newb
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thanks for the explanation I see the intention. I was curious. Stef On Apr 22, 2010, at 6:55 PM, Eliot Miranda wrote: > > > On Thu, Apr 22, 2010 at 12:49 AM, stephane ducasse <[hidden email]> wrote: > > > Yes. But MethodContext behaves differently depending on whether its closureOrNil inst var is nil (a normal method) or a BlockClosure (an activation of a block). If nil, ^-returns return to the context's sender. If not nil ^-returns return from the home context, found by following the outerContext chain through the closureOrNil inst var. So we no longer need BlockContext. > > > Hi Elliot > > I was wondering why you do not use two classes and you do the nil check? > > One reason is backward compatibility. The existing VM ensures that closureOrNil (which used to be called receiverMap) is nil. The other is the internal workings of the VM. The nil test is done by the VM on every ^-return. The VM isn't going to waste time sending a message. It is going to do a nil test. > > In fact in Cog the VM doesn't even do a nil test since in machine code the JIT knows at compile time whether an ^-return is within a block or not, and in the stack interpreter whether a frame is a block activation is indicated by a status bit in the method field of a frame. > > So don't think Smalltalk code, think optimized VM internals. We're not going to waste time instantiating some object just to tag a structure as not being a block activation. > > HTH > Eliot > > > > This also means we only need one context class, and some time I'd like to merge the two ContextPart and MethodContext classes into a single Context class. Possibly the name should be ExecutionContext or MethodOrBlockContext or? Suggestions? > > > > > > Now, test yourself before evaluating :) what should be the result of > > this expression? > > > > [: arg | arg perform: #isExecutingBlock ] value: thisContext > > > > It depends on whether the expression is executed at method level or at block level. As a test this should be: > > > > testIsExecutingBlock > > self assert: ([: arg | arg perform: #isExecutingBlock ] value: thisContext) == false. > > [self assert: ([: arg | arg perform: #isExecutingBlock ] value: thisContext) == true] value > > > > Can somebody justify the result? > > > > isExecutingBlock answers if the receiver is executing a block or not. It does not answer whether the context in which isExecutingBlock is sent is executing a block or not. Remember that > > > > [:arg| arg == thisContext] value: thisContext > > > > is false. thisContext is rebound within every actual method or block scope. > > > > HTH > > > > Eliot > > > > > > >> Context creation is optimized in the VM in most Smalltalks, so it's > > >> only really created as an object in the environment (reified) when > > >> it's specifically needed through "thisContext". > > > > > > In Pharo contexts are not reified like that. Stack-frames are actual > > > objects at all times. However, for speed reasons, their creation and > > > garbage-collection is optimized by the VM. Stack frames get > > > automatically recycled if nobody refers to them. > > > > > > > I think is what I said :) > > > > But its not a property of Pharo. It is a property of the VM. In Cog contexts are not actual objects all the time, only when needed. And Cog runs Pharo images just as it runs Squeak images. So it would be incorrect to say "in Pharo" and better to say "in the standard Squeak VM". > > > > > > >> There are several applications related with computational reflection > > >> (Reflective Programming, Meta-Programming, MOP, etc) which makes use > > >> of the current context. > > > > > > Also: exception handling, generators, continuations, co-routines, ... > > > > > > For another fun use of "thisContext" check this Stack-Overflow question: > > > > > > http://stackoverflow.com/questions/2500483/is-there-a-way-in-a-message-only-language-to-define-a-whiletrue-message-without-r > > > > > > Lukas > > > > > > -- > > > Lukas Renggli > > > www.lukas-renggli.ch > > > > > > _______________________________________________ > > > Pharo-project mailing list > > > [hidden email] > > > http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project > > > > > > > _______________________________________________ > > Pharo-project mailing list > > [hidden email] > > http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project > > > > |
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