Một biểu thức, tất nhiên, có thể là một biểu tượng riêng của mình hoặc một danh sách. Trong Emacs Lisp mã, một biểu hiện tiết kiệm-tham quan thường xảy ra trong cơ thể của một biểu thức cho phép. Nó trông như thế này: (chúng ta hãy varlist (.)) cơ thể tiết kiệm-tham quan | 46 Chapter 3 How To Write Function Definitions In more detail the template for a save-excursion expression looks like this save-excursion hrst-expression-in-body second-expression-in-body third-expression-in-body . last-expression-in-body An expression of course may be a symbol on its own or a list. In Emacs Lisp code a save-excursion expression often occurs within the body of a let expression. It looks like this let varlist save-excursion body. Review In the last few chapters we have introduced a fair number of functions and special forms. Here they are described in brief along with a few similar functions that have not been mentioned yet. eval-last-sexp Evaluate the last symbolic expression before the current location of point. The value is printed in the echo area unless the function is invoked with an argument in that case the output is printed in the current buffer. This command is normally bound to C-x C-e. defun Define function. This special form has up to five parts the name a template for the arguments that will be passed to the function documentation an optional interactive declaration and the body of the definition. For example defun back-to-indentation Move point to first visible character on line. interactive beginning-of-line 1 skip-chars-forward t interactive Declare to the interpreter that the function can be used interactively. This special form may be followed by a string with one or more parts that pass the information to the arguments of the function in sequence. These parts may also tell the interpreter to prompt for information. Parts of the string are separated by newlines n . Review 47 Common code characters are b The name of an existing buffer. f The name of an existing file. p The numeric prefix argument. Note that this p is lower case. r Point and the mark as two numeric arguments smallest first. This is the only code letter that specifies two successive arguments rather than one. See section Code Characters for interactive in The .
