Distinguishing between Atoms and Symbols in LISP

Upon closer examination, it seems that public documentation about LISP cites Atoms as an especially simple example of Symbols, that just have an empty Property List (NIL). It is written that they are first created that way by default.

Otherwise, Symbols are capable of carrying Values, which could just be another Atom, or which could be represented by a List in turn, whose first element is a type-atom.

It seems that in my writings, I have just reversed this use of the terms ‘Symbol’ and ‘Atom’. My main reason for not correcting this, is the fact that it would be too complicated to go back and edit so much.

I apologize for this apparent error, but will stick to it for the sake of consistency.

When Function definitions are written, Atoms and Keywords are given that bear no initial value, and which therefore, according to popular documentation, are not fully Symbols yet. These Atoms would be of no usefulness, if during the Evaluation of LISP expressions, they could not be bound to Values with local scope at least. So any Atom can trivially be promoted to a Symbol.

The other Atoms need to state Functions or Macros.

And in cases where they are type-atoms, their value can be a parent type, again leading to an Atom. So those examples should not have NIL as their Property, because the parent-type for all types, is supposed to be T and not NIL. If a type-atom was to have NIL as its ultimate parent, it would just refer to some unrecognized type, outside the LISP Interpreter scope for how to Evaluate.

Dirk

 

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