Re: Calling a function with undefined symbol

[Heime <heimeborgia@protonmail.com>]

------- Original Message -------
On Monday, October 31st, 2022 at 9:58 AM, Jean Abou Samra <jean@abou-samra.fr> wrote:


> > Le 31 oct. 2022 à 10:45, Heime heimeborgia@protonmail.com a écrit :
> > 
> > ------- Original Message -------
> > On Monday, October 31st, 2022 at 9:24 AM, Jean Abou Samra jean@abou-samra.fr wrote:
> > 
> > > > > Le 31 oct. 2022 à 09:59, Heime heimeborgia@protonmail.com a écrit :
> > > > 
> > > > Yes, I have got really confused about what symbols are exactly. Even
> > > > after reading several times. I have never seen anybody make a symbol,
> > > > only variables. So, what is a symbol?
> > > 
> > > Imagine parents who are planning to have a child and decide they will call it, say Deborah. They will say things like “I like the name Deborah better than Mary”. Those are sentences about the names themselves, not some children. The names don’t need children in order to exist as words. Then, the child is born and sentences like “Deborah weighs 3kg” (referring to the child named Deborah) start to make sense.
> > > 
> > > When you do 'symbol in Lisp, this gives you a bare name, or a “symbol”. With symbol-value, you get what value is associated with this symbol, if any (the child with that name). But you don’t need a value bound to the symbol (a child called Deborah) before you start using the symbol itself (the name “Deborah”).
> > 
> > The Lisp manual says that a symbol is an object with a name.
> 
> 
> 
> This can be interpreted as the correct definition, but also as a wrong definition where a symbol is necessarily associated with a defined variable. Better said: a symbol is an object that represents a name.
> 
> > Then a variable (setq thevar 4) has an associated symbol 'thevar.
> > And the function "(defun thefun ()" also has an associated symbol "'thefun". Furthermore one can make just a symbol, let us say 'go,
> > which can be passed as an argument to a function "(defun mbcomplt (arg)" using (mbcomplt 'go).
> 
> 
> 
> Yes. The symbol is an object like any other (5, "foo", whatever), so what you can do with an object, you can do with a symbol, including passing it as an argument to a function.
> 
> > Then inside the function on can test
> > whether the symbol exists with (eq arg 'go).
> 
> 
> 
> That is not testing whether the symbol “exists”. It is testing whether arg is the symbol 'go.

Thank you for the clarification.  I now understand it.
 
> > Even though we only have a name without a values. Is this a good basic understanding
> > of a symbol?
> 
> 
> 
> Apart from the last part, yes.
 
Great, thank you.