Create self-modifying Lisp program and introduce a new investigation line.

[izzortsi]

Created a self-modifying Lisp program that demonstrates homoiconicity by reading its own source code, incrementing a generation counter, and rewriting itself. Includes comprehensive documentation explaining the concept, how it works, and how to run it.

[Copilot]

Pull Request Overview

This PR introduces a new investigation line focused on Gödel machines and self-rewriting programs, demonstrating homoiconicity through practical Lisp implementations. The PR includes both minimal and robust versions of self-modifying programs along with comprehensive documentation explaining the theoretical foundations and practical implications.

Key Changes:

• Implements two self-modifying Lisp programs (minimal and robust versions) that demonstrate code-as-data
• Adds theoretical documentation on Gödel machines and recursive self-improvement
• Provides comprehensive README files with examples, comparisons, and educational content

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
self-rewriting.lisp	Minimal self-modifying program using string manipulation to increment a generation counter
self-rewriting-robust.lisp	Advanced version using S-expression parsing for robust code manipulation with evolution capabilities
project-summary.md	Theoretical overview of Gödel machines with academic references and research questions
README_SELF_REWRITING.md	Documentation for the minimal version explaining homoiconicity and basic self-modification
README_ROBUST_SELF_REWRITING.md	Detailed documentation for the robust version with technical comparisons and execution examples
README.md	Main project README providing overview, key concepts, and project structure

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[Copilot]

This direct mutation of a shared data structure can cause unexpected behavior. The gen-form is a reference to an element in sexprs, so modifying it with setf mutates the input list. This violates the principle of least surprise and can lead to bugs if the caller expects sexprs to remain unchanged. Consider creating a modified copy of the list instead or documenting this side effect clearly.

Suggested change

	"Increment the *generation* value in a list of S-expressions"
	(let ((gen-form (find-defparameter-form '*generation* sexprs)))
	(if gen-form
	(progn
	(setf (third gen-form) (1+ (third gen-form)))
	sexprs)
	(error "Could not find *generation* defparameter"))))
	"Increment the *generation* value in a list of S-expressions, returning a modified copy"
	(let ((found nil))
	(let ((new-sexprs
	(mapcar (lambda (form)
	(if (and (listp form)
	(eq (car form) 'defparameter)
	(eq (cadr form) '*generation*))
	(progn
	(setf found t)
	`(defparameter *generation* ,(1+ (third form))))
	form))
	sexprs)))
	(if found
	new-sexprs
	(error "Could not find *generation* defparameter"))))

[Copilot]

Potential nil dereference. If find-defparameter-form returns nil (when *generation* is not found), calling (third nil) will return nil, which will then cause (= new-generation (1+ original-gen)) to fail with a type error since = expects numbers. The function should handle the case where the generation parameter might not be found in the parsed expressions.

Suggested change

	(new-generation (third (find-defparameter-form '*generation* sexprs))))
	(if (= new-generation (1+ original-gen))
	(format t "✓ Self-modification successful!~%")
	(format t "✗ Self-modification failed! Expected ~a, found ~a~%"
	(1+ original-gen) new-generation)))))
	(gen-form (find-defparameter-form '*generation* sexprs)))
	(if gen-form
	(let ((new-generation (third gen-form)))
	(if (= new-generation (1+ original-gen))
	(format t "✓ Self-modification successful!~%")
	(format t "✗ Self-modification failed! Expected ~a, found ~a~%"
	(1+ original-gen) new-generation)))
	(format t "✗ Self-modification failed! Could not find *generation* defparameter in source.~%"))))

[Copilot]

The push operations in lines 59-60 and 73 add new forms to the beginning of the sexprs list (due to push prepending), but this can result in incorrect code structure. Comments and new definitions will appear at the top of the file, before the shebang line and existing definitions. This will likely break the program's executability and structure. Consider using append or inserting at appropriate positions instead.

[Copilot]

Inefficient repeated lookups. The code calls find-defparameter-form '*generation* sexprs twice (lines 53-54), duplicating the same search operation. Consider storing the result in a variable to improve performance and code clarity.

Suggested change

	(let ((gen-form (find-defparameter-form '*generation* sexprs))
	(current-gen (third (find-defparameter-form '*generation* sexprs))))
	(let* ((gen-form (find-defparameter-form '*generation* sexprs))
	(current-gen (third gen-form)))

[Copilot]

Spelling error: "Goedel" should be "Gödel" to match the standard academic spelling used elsewhere in the documentation (e.g., line 1 of README.md and other references).

Suggested change

	**Goedel machines: Self-Referential Universal Problem Solvers Making Provably Optimal Self-Improvements**
	**Gödel machines: Self-Referential Universal Problem Solvers Making Provably Optimal Self-Improvements**

[Copilot]

[nitpick] Inconsistent terminology: The documentation uses "defparameter" without backticks or code formatting in this context, but it refers to a Lisp keyword that should be formatted as code. For consistency with other parts of the documentation (e.g., line 173 in README_ROBUST_SELF_REWRITING.md), consider using backticks: `defparameter`.

[izzortsi]

@copilot open a new pull request to apply changes based on this feedback

[Copilot]

@izzortsi I've opened a new pull request, #105, to work on those changes. Once the pull request is ready, I'll request review from you.

[izzortsi]

@copilot open a new pull request to apply changes based on the comments in this thread

[Copilot]

@izzortsi I've opened a new pull request, #106, to work on those changes. Once the pull request is ready, I'll request review from you.