eintr: Names & Definitions
1.4 Symbol Names and Function Definitions
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We can articulate another characteristic of Lisp based on what we have
discussed so far—an important characteristic: a symbol, like ‘+’, is not
itself the set of instructions for the computer to carry out. Instead,
the symbol is used, perhaps temporarily, as a way of locating the
definition or set of instructions. What we see is the name through
which the instructions can be found. Names of people work the same way.
I can be referred to as ‘Bob’; however, I am not the letters ‘B’, ‘o’,
‘b’ but am, or was, the consciousness consistently associated with a
particular life-form. The name is not me, but it can be used to refer
to me.
In Lisp, one set of instructions can be attached to several names.
For example, the computer instructions for adding numbers can be linked
to the symbol ‘plus’ as well as to the symbol ‘+’ (and are in some
dialects of Lisp). Among humans, I can be referred to as ‘Robert’ as
well as ‘Bob’ and by other words as well.
On the other hand, a symbol can have only one function definition
attached to it at a time. Otherwise, the computer would be confused as
to which definition to use. If this were the case among people, only
one person in the world could be named ‘Bob’. However, the function
definition to which the name refers can be changed readily. (
Install a Function Definition Install.)
Since Emacs Lisp is large, it is customary to name symbols in a way
that identifies the part of Emacs to which the function belongs. Thus,
all the names for functions that deal with Texinfo start with ‘texinfo-’
and those for functions that deal with reading mail start with ‘rmail-’.
Info Catalog
eintr: Making Errors
eintr: List Processing
eintr: Lisp Interpreter