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Programming in Emacs Lisp

1.7.1 Error Message for a Symbol Without a Function

When we evaluated fill-column to find its value as a variable, we did not place parentheses around the word. This is because we did not intend to use it as a function name.

If fill-column were the first or only element of a list, the Lisp interpreter would attempt to find the function definition attached to it. But fill-column has no function definition. Try evaluating this:

(fill-column)

In GNU Emacs version 21, you will create a `*Backtrace*' buffer that says:

---------- Buffer: *Backtrace* ---------- Debugger entered--Lisp error: (void-function fill-column) (fill-column) eval((fill-column)) eval-last-sexp-1(nil) eval-last-sexp(nil) call-interactively(eval-last-sexp) ---------- Buffer: *Backtrace* ----------

(Remember, to quit the debugger and make the debugger window go away, type q in the `*Backtrace*' buffer.)

In GNU Emacs 20 and before, you will produce an error message that says:

Symbol's function definition is void: fill-column

(The message will go away away as soon as you move the cursor or type another key.)