Re: Calling a function with undefined symbol

[Heime]

------- 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.