Hi Eliot, this sounds like a reasonable piece of work. I'll need to reverse-engineer all the relevant stuff first, but it will put it onto my list with a priority above average :)


One question in general, both index and code appear to be referenced by LeafNode itself mainly for accessing and initialization purposes. Why can't we define these inst vars per subclass and use an abstract getter in LeafNode (if necessary at all)? I have the feeling that this could simplify explanation and understanding of the several meanings of index.

Best,
Christoph
________________________________
Von: Squeak-dev <squeak-dev-bounces at lists.squeakfoundation.org> im Auftrag von Eliot Miranda <eliot.miranda at gmail.com>
Gesendet: Sonntag, 29. März 2020 19:49:33
An: The general-purpose Squeak developers list
Betreff: Re: [squeak-dev] Decompiler buggy (was: AW: [Etoys, Compiler] Help wanted: Trying to embed SyntaxMorphs into other tiles)

Hi Christoph,

    please read what I'm about to say carefully.  This message is aimed at you :-)

On Sat, Mar 28, 2020 at 6:09 AM Nicolas Cellier <nicolas.cellier.aka.nice at gmail.com<mailto:nicolas.cellier.aka.nice at gmail.com>> wrote:
Hi Christoph,

Le sam. 28 mars 2020 à 01:12, Thiede, Christoph <Christoph.Thiede at student.hpi.uni-potsdam.de<mailto:Christoph.Thiede at student.hpi.uni-potsdam.de>> a écrit :

Hi Eliot, hi all,


ah, I finally found the bug, but this was a really hard hunt! :D


The solution is absolutely simple, again:


codeAnySelector: selector


^SelectorNode new

key: selector

+ index: nil

- index: 0

type: SendType

Good find!

Seriously, did the Decompiler ever reliably produce re-generatable parse trees in the past? But it should do so, shouldn't it? :-)

Maybe it did (see below). But I'm not sure that is was a feature...
Isn't it mostly used for replacing absent source code... that will eventually be repasrsed ? (!)

Before the above patch, the following example was broken, too:

class := Object newSubclass.
class compile: 'foo ^ 1 + 1'.
(class >> #foo) decompile generate valueWithReceiver: class new arguments: #(). "SmallInteger does not understand #foo"

Now I'm wondering what are the actual semantics of the index variable. Its method comment about "various uses depending on the class of the receiver" is quite generic - do you know some more details about this?
Should we also use nil instead of 0 in DecompilerConstructor >> #codeAnyLiteral:? At first glance, senders of #encodeLiteral: do not appear to set it to zero manually (so they leave it nil), but unless there is any documentation of the index meaning, this is speculation only, as I could not find any other example where decompilation + regeneration produce a method that cannot be executed properly.

It's very low level, some kind of reflexion of byteCode encoding.
Once upon a time (< Squeak4.0), the code was even more horrible to follow!

LeafNode>>key: object index: i type: type
    self key: object code: (self code: i type: type)

LeafNode>>code: index type: type
    index isNil
         ifTrue: [^type negated].
     (CodeLimits at: type) > index
         ifTrue: [^(CodeBases at: type) + index].
     ^type * 256 + index

Exactly.  This is actually obsolete genius by Dan Ingalls.  If you have a look at the original Smalltalk-80 bytecode compiler you'll see that the parse tree nodes both represent the parse tree *and* generate the output bytecodes,  This was really important on 16-bit Smalltalk-80 since it meant that the bytecode compiler was extremely compact and concise.  Objects were in extremely short supply, 32k objects in a normal implementation (with 15-bit SmallIntegers), and 48k objects in a "stretch" implementation that had 14-bit SmallIntegers.

Now we have 32-bit and 64-bit implementations this concision is obsolete and what we need is flexibility and clarity.

I had done some reimplementation work on the bytecode compiler in 2009 to add the closure bytecodes, and to add a proper code generation back end in the BytecodeEncoder framework, but I never finished the cleanup. The index and code inst vars in the LeafNode hierarchy are vestiges of the old implementation.  It would be really good to get rid of the code inst var altogether and to be left only with index, and index being the literal index for literal nodes (perhaps negative indices being used for special selectors), index being the inst var index for inst var nodes, and index being the temp var offset for temp var nodes, etc.

But this really needs someone with fresh eyes and energy.  My plate is full.  When I did think of doing this I realized that it is probably wise to clone the compiler altogether and do the development and testing work in the clone before moving it back to LeafNode et al for the first functional commit.  This to avoid breaking the compiler while trying to fix it.

So Christoph, do you accept my challenge and will you try and eliminate the code inst var from LeafNode?



As you see, index i passed as argument to #code: keyword (? it's because it's documenting the output, not the input);
then code: parameter shadowing the index instance variable...
And the index instance variable was not set... Kind of brainfuck.

We still have code:type: and index variable shadowing in current trunk...

By the way, here is another interesting one-liner:

(Object newSubclass environment: self environment; compile: 'foo ^(ObjectTracer on: nil) class'; >> #foo) decompile generate valueWithReceiver: nil arguments: #()

Interestingly, it opens a debugger - in other words, #class is sent as a regular selector. The decompiler does not know anything about special selectors at the moment. Is this desired behavior? I wonder whether it should be the parse tree's responsibility to install such kind of optimizations, rather than the responsibility of the Compiler.
Because in reality, Compiler is not the only client that requests code generation from parse trees. Etoys is a good example for a client from another domain that uses this service, too. Should all these other clients be withheld these important optimizations of Smalltalk expressions?

After parsing, there are other compilation phases, for analyzing variable scope, clean blocks, etc...
It's possible to scatter the implementation of various phases in the nodes themselves, but the trend is rather to use a visitor pattern;
it gather the handling in some specialized classes that hold all the states (rather than pass them as message arguments).
Pharo team did a complete re-engineering of compiler (OpalCompiler) that you culd study.

Best,
Christoph

________________________________
Von: Thiede, Christoph
Gesendet: Freitag, 27. März 2020 23:16 Uhr
An: The general-purpose Squeak developers list
Betreff: AW: [squeak-dev] [Etoys, Compiler] Help wanted: Trying to embed SyntaxMorphs into other tiles


Hi Eliot,


> It looks correct.  Can you check it against the old bytecode set too?  We don’t want it to break old-style blocks.

Good point. I ran

(Object >> #asOrderedCollection) decompile generate valueWithReceiver: 42 arguments: #().

for both bytecode sets, and both were fine.

But:

(Collection >> #asArray) decompile generate valueWithReceiver: {42} asOrderedCollection arguments: #().

breaks - in both bytecode sets. This is weird.
I will have a look into it, maybe I can discover what's wrong.

In addition, I propose to write tests for this. But it's not the goal of the decompiler to yield exactly the same parse tree or source code as the original method consisted of? In this case, we will need to write a lot of fixtures for the tests.

Best,
Christoph


________________________________
Von: Squeak-dev <squeak-dev-bounces at lists.squeakfoundation.org<mailto:squeak-dev-bounces at lists.squeakfoundation.org>> im Auftrag von Eliot Miranda <eliot.miranda at gmail.com<mailto:eliot.miranda at gmail.com>>
Gesendet: Freitag, 27. März 2020 21:33 Uhr
An: The general-purpose Squeak developers list
Betreff: Re: [squeak-dev] [Etoys, Compiler] Help wanted: Trying to embed SyntaxMorphs into other tiles

Hi Christoph,

On Mar 27, 2020, at 12:45 PM, Thiede, Christoph <Christoph.Thiede at student.hpi.uni-potsdam.de<mailto:Christoph.Thiede at student.hpi.uni-potsdam.de>> wrote:



Hi all! :-)

Just an update of the decompilation question:
Christoph Thiede wrote
I don't know how to use #generate: exactly, but other senders usually appear to recompile a method before passing it to #generate:.
For comparison:

[ (Collection >> #asArray) decompile generate: CompiledMethodTrailer empty ] fails, but

[ m := (Collection >> #asArray) decompile.

  m := Compiler new compile: m in: Collection notifying: nil ifFail: #foo.
  m generate: CompiledMethodTrailer empty ] works.
Why is that recompilation required but decompilation is insufficient? Is this some bug, or is it expected behavior?
The general approach seems to be correct, but I think I found an error in the decompilation of literal variables such as Array. I sent Compiler-ct.425 to the inbox which should fix this issue.

I moved this to inbox.  It looks correct.  Can you check it against the old bytecode set too?  We don’t want it to break old-style blocks.

<http://www.hpi.de/>

I am going to complete the implementation of SyntaxMorph >> #parseNode :-)

Best,
Christoph
________________________________
Von: Squeak-dev <squeak-dev-bounces at lists.squeakfoundation.org<mailto:squeak-dev-bounces at lists.squeakfoundation.org>> im Auftrag von Thiede, Christoph
Gesendet: Dienstag, 15. Oktober 2019 21:08:24
An: squeak-dev at lists.squeakfoundation.org<mailto:squeak-dev at lists.squeakfoundation.org>
Betreff: [squeak-dev] [Etoys, Compiler] Help wanted: Trying to embed SyntaxMorphs into other tiles


Hi all,


I'm currently trying to implement #parseNodeWith: on SyntaxMorph, in order to embed SyntaxMorphs into regular tiles. (Did this ever work in past?)

I'm afraid the attempt in the commit below does not work yet; you can create a script editor, but parsing is erroneous, so you cannot execute the script.


To reproduce:

Compile the following:

MyPlayer >> examplePlayerCode

self forward: 6 * 7.

self turn: (11 raisedTo: 13 modulo: 97)

and evaluate:

| e p |
p := Morph new openInWorld assuredPlayer.
e := (MyPlayer >> #examplePlayerCode) decompile asScriptEditorFor: p.
e openInHand.


In Player>>#acceptScript:for:, #generate: is called on node, and when I decompile the result, I get a strange result:


examplePlayerCodeTest

self forward: 6 * 7.

self

forward: (#forward: forward: #forward:).


I don't know how to use #generate: exactly, but other senders usually appear to recompile a method before passing it to #generate:.

For comparison:

[ (Collection >> #asArray) decompile generate: CompiledMethodTrailer empty ] fails, but

[ m := (Collection >> #asArray) decompile.

  m := Compiler new compile: m in: Collection notifying: nil ifFail: #foo.
  m generate: CompiledMethodTrailer empty ] works.

Why is that recompilation required but decompilation is insufficient? Is this some bug, or is it expected behavior?


However, in the case of SyntaxMorph, I don't know how to recompile the node before, as a SyntaxMorph should be able to represent a node of an arbitrary type that must not be constrained to a MessageNode. So how could I solve the problem to generate code from SyntaxMorphs?


tl;dr: What is the full story of #generate: and how can it be made to work in this example?

Many thanks in advance! :-)


Best,

Christoph

________________________________
Von: Squeak-dev <squeak-dev-bounces at lists.squeakfoundation.org<mailto:squeak-dev-bounces at lists.squeakfoundation.org>> im Auftrag von commits at source.squeak.org<mailto:commits at source.squeak.org> <commits at source.squeak.org<mailto:commits at source.squeak.org>>
Gesendet: Dienstag, 15. Oktober 2019 14:46 Uhr
An: squeak-dev at lists.squeakfoundation.org<mailto:squeak-dev at lists.squeakfoundation.org>
Betreff: [squeak-dev] The Inbox: EToys-ct.367.mcz

A new version of EToys was added to project The Inbox:
http://source.squeak.org/inbox/EToys-ct.367.mcz

==================== Summary ====================

Name: EToys-ct.367
Author: ct
Time: 15 October 2019, 2:46:24.862129 pm
UUID: 1394344f-b1e3-5640-a13a-70c5dffd51f4
Ancestors: EToys-mt.361

Allow for embedding SyntaxMorphs into test tiles.

=============== Diff against EToys-mt.361 ===============

Item was added:
+ ----- Method: SyntaxMorph>>parseNodeWith:asStatement: (in category '*Etoys-Squeakland-code generation') -----
+ parseNodeWith: encoder asStatement: aBoolean
+
+        ^ self parseNode!







--
_,,,^..^,,,_
best, Eliot
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