Fun with AST evaluation

Hi,

This is fun experiment:

Every RBValueNode subclass evaluates to something. So why not implement a #evaluate method?

This is especially fun to do for a specific context, as this means that you could evaluate every RBVariableNode to see the value.

So lets implement a method in RBValueNode:

evaluateWithContext: aContext

| methodNode |

If we want to compile a method for it, we need to wrap it into a return and a method. Like when evaluating in the debugger, we create a #DoItIn: method that

will get the context as a parameter to read the values from (temps from the context, ivars from context receiver).

This works like this:

methodNode := RBMethodNode 

selector: #DoItIn:

arguments: { RBVariableNode named: 'ThisContext' } 

body: (RBReturnNode value: self) asSequenceNode.

to read temps from the context parameter, we use the rewrite method that is used by doits already:

methodNode rewriteTempsForContext: aContext.

and now we can execute:

^methodNode generate valueWithReceiver: aContext receiver arguments: {aContext}.

For testing, I put a #haltOnce into Rectangle>>#area and then use the inspector on the context to evaluate a AST node that is a temporary variable.

The screenshot shows executing

self method ast assignmentNodes first variable evaluateWithContext: self

and it returns correctly 104:

Of course there are simpler ways to read variables by name from a context (e.g. we added #lookupSymbol: ), but #evaluateWithContext: can be called on other Nodes, too.

E.g. just a #evaluate could be nice for creating Blocks programmatically (instead of calling the compiler on a Pretty-Print result like #createBlockFor: in the ParseTreeSearcher).

A version that does not take context and receiver into account is this:

evaluate

| methodNode |

methodNode := RBMethodNode 

selector: #DoIt

body: (RBReturnNode value: self) asSequenceNode.

^methodNode generate valueWithReceiver: nil arguments: #().

and then you can do things like

blockNode: = RBBlockNode

body: (RBLiteralNode value: 5) asSequenceNode

blockNode evaluate

to create blocks.

Marcus

Now clement what is the difference with a plain AST interpreter?

On Tue, Apr 17, 2018 at 6:57 PM, Clément Bera <[hidden email]> wrote:

Starting from here you can build a full AST interpreter that mutates a context instance that you create by interpreting MessageNode...

On Tue, Apr 17, 2018 at 5:45 PM, Marcus Denker <[hidden email]> wrote:

Hi,

This is fun experiment:

Every RBValueNode subclass evaluates to something. So why not implement a #evaluate method?

This is especially fun to do for a specific context, as this means that you could evaluate every RBVariableNode to see the value.

So lets implement a method in RBValueNode:

evaluateWithContext: aContext

| methodNode |

If we want to compile a method for it, we need to wrap it into a return and a method. Like when evaluating in the debugger, we create a #DoItIn: method that

will get the context as a parameter to read the values from (temps from the context, ivars from context receiver).

This works like this:

methodNode := RBMethodNode 

selector: #DoItIn:

arguments: { RBVariableNode named: 'ThisContext' } 

body: (RBReturnNode value: self) asSequenceNode.

to read temps from the context parameter, we use the rewrite method that is used by doits already:

methodNode rewriteTempsForContext: aContext.

and now we can execute:

^methodNode generate valueWithReceiver: aContext receiver arguments: {aContext}.

For testing, I put a #haltOnce into Rectangle>>#area and then use the inspector on the context to evaluate a AST node that is a temporary variable.

The screenshot shows executing

self method ast assignmentNodes first variable evaluateWithContext: self

and it returns correctly 104:

Of course there are simpler ways to read variables by name from a context (e.g. we added #lookupSymbol: ), but #evaluateWithContext: can be called on other Nodes, too.

E.g. just a #evaluate could be nice for creating Blocks programmatically (instead of calling the compiler on a Pretty-Print result like #createBlockFor: in the ParseTreeSearcher).

A version that does not take context and receiver into account is this:

evaluate

| methodNode |

methodNode := RBMethodNode 

selector: #DoIt

body: (RBReturnNode value: self) asSequenceNode.

^methodNode generate valueWithReceiver: nil arguments: #().

and then you can do things like

blockNode: = RBBlockNode

body: (RBLiteralNode value: 5) asSequenceNode

blockNode evaluate

to create blocks.

Marcus

--

Clément Béra
https://clementbera.github.io/

https://clementbera.wordpress.com/