science

ObjVlisp

ObjVlisp is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand ObjVlisp rather than just read about it. In short: ObjVlisp is a 1984 object-oriented extension of Vlisp–Vincennes LISP, a LISP dialect developed since 1971 at the University of Paris VIII – Vincennes. It is noteworthy as one of the earliest implementations of the concept of metaclasses, and in particular explicit (as opposed to implicit) metaclasses.

Key takeaways

ObjVlisp belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect ObjVlisp to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of ObjVlisp from memory before moving on to harder problems.

Reference excerpt

ObjVlisp is a 1984 object-oriented extension of Vlisp–Vincennes LISP, a LISP dialect developed since 1971 at the University of Paris VIII – Vincennes. It is noteworthy as one of the earliest implementations of the concept of metaclasses, and in particular explicit (as opposed to implicit) metaclasses. In the ObjVlisp model, "each entity is an instance of a single class. Classes are instances of other classes, called metaclasses. This model allows for extension of the static part of OOL, i.e. the structural aspects of objects considered as implementation of abstract data types" ObjVlisp provided a far more flexible metaclass model than that provided by earlier object-oriented languages, especially Smalltalk. In Smalltalk-80, whenever a new class is created, a corresponding metaclass is created automatically; it does not have a name independent of that of the metaclass for which it was created–metaclasses are implicit rather than explicit. By contrast, in ObjVlisp, it is possible to define named metaclasses, and when defining a class one must specify which named metaclass it will instantiate. The explicit metaclass support in ObjVlisp influenced the provision of the same capability in the Common Lisp Object System. The ObjVlisp object model was later implemented in Prolog to produce ObjVProlog. Both Python and Converge implement a meta-class system that is equivalent of that of ObjVLisp.

References

Worked examples

Example 1 — a first encounter with ObjVlisp

Start with the simplest possible case. Write down what ObjVlisp claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to ObjVlisp before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about ObjVlisp ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of ObjVlisp

In research: ObjVlisp appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses ObjVlisp in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: ObjVlisp is common in secondary-school and first-year university syllabi. It links to neighbouring topics Lisp programming language family, Object-oriented programming languages, Programming language topic stubs, so understanding it makes those chapters shorter.
In everyday life: Look for ObjVlisp outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study ObjVlisp in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what ObjVlisp means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain ObjVlisp out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is ObjVlisp in simple terms?

Why does ObjVlisp matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study ObjVlisp?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on ObjVlisp.