Debra Cameron - Learning GNU Emacs, 3rd Edition

Here's an example of a macro that puts a business letter template on the screen and uses recursive edits to let you type your return address, the recipient's name and address, and the date. Because the brackets on the mode line are a pretty subtle clue to what you are going to type, we'll give the user of this macro explicit instructions about what to type. Table 6-3provides these instructions.

Table 6-3. Steps for creating a business letter macro

The following screens show what the macro defined in Table 6-3looks like when you run it.

Type: F4

The macro pauses so that you can type your address.

Type your address and press: C-M-c

The macro pauses so you can type the recipient's name and address.

Type the recipient's name and address and press: C-M-c

The macro pauses so you can type the date.

Type the date and press: C-M-c

The macro finishes by typing the opening for the letter.

Now the macro has finished editing; you can type the recipient's name and then the body of the letter, and of course you can go back and edit any of the information you've already filled in.

The more complex the task your macro performs, the more difficult it is to make the macro general enough to work in every case. Although macros can do a lot of things, they aren't programs: you can't have ifstatements, loops, and the other things you associate with a program. In particular, a macro can't get input from the user and then take some action on the basis of that input.

However, one feature lets a macro get input, in a limited way, from the user. You can create a macro that queries the user while it is running; it works much like a query-replace. To create this kind of a macro, type C-x qwhen you reach the point in the macro definition where you want the macro to query the user. Nothing happens immediately; go on defining the macro as you normally would.

Things get interesting later, when you execute the macro. When it gets to the point in the macro where you typed C-x q, Emacs prints a query in the minibuffer:

Proceed with macro? (y, n, RET, C-l, C-r)

The responses listed here are analogous to those in query-replace:

• Pressing ymeans to continue and go on to the next repetition, if any.

• Pressing nmeans to stop executing the macro but go on to the next repetition, if any.

• Pressing Entermeans to stop executing the macro and cancel any repetitions.

• Pressing C-rstarts a recursive edit, which lets you do any editing or moving around you may want to and then resume the macro when you exit the recursive edit. To exit a recursive edit, press C-M-c. Emacs again asks if you want to proceed with the macro, and you type yfor yes or nor Enterfor no.

• Pressing C-lputs the line the cursor is on in the middle of the screen (this is good for getting a feel for the context). Similar to C-r, Emacs again asks if you want to proceed with the macro, and you have to answer y, n, or Enter.

• Pressing C-g(although not listed as an option) cancels the query and the macro; it is similar to pressing Enter.

Let's say that you write a macro that copies comments from a program to another buffer. The comments in our program are preceded by a slash, so you start the macro with a search for a slash. However, not all comments are worth copying. Following the search with a query lets you decide case by case whether the search has found a comment you want to copy. Table 6-4shows a macro to copy comments to another buffer.

Table 6-4. Comment-copying macro with a query