The usual Emacs comment commands assume that a comment can follow a line of code. In Fortran, the standard comment syntax requires an entire line to be just a comment. Therefore, Fortran mode replaces the standard Emacs comment commands and defines some new variables.
Fortran mode can also handle a nonstandard comment syntax where comments
start with `!' and can follow other text. Because only some Fortran
compilers accept this syntax, Fortran mode will not insert such comments
unless you have said in advance to do so. To do this, set the variable
comment-start to `"!"' (see section Variables).
M-; in Fortran mode is redefined as the command
fortran-comment-indent. Like the usual M-; command, this
recognizes any kind of existing comment and aligns its text appropriately;
if there is no existing comment, a comment is inserted and aligned. But
inserting and aligning comments are not the same in Fortran mode as in
When a new comment must be inserted, if the current line is blank, a full-line comment is inserted. On a non-blank line, a nonstandard `!' comment is inserted if you have said you want to use them. Otherwise a full-line comment is inserted on a new line before the current line.
Nonstandard `!' comments are aligned like comments in other
languages, but full-line comments are different. In a standard full-line
comment, the comment delimiter itself must always appear in column zero.
What can be aligned is the text within the comment. You can choose from
three styles of alignment by setting the variable
fortran-comment-indent-style to one of these values:
fortran-comment-line-extra-indentand the minimum statement indentation. This is the default. The minimum statement indentation is
fortran-minimum-statement-indent-fixedfor fixed format continuation line style and
fortran-minimum-statement-indent-tabfor tab format style.
fortran-comment-line-extra-indentcolumns of indentation.
In addition, you can specify the character to be used to indent within
full-line comments by setting the variable
fortran-comment-indent-char to the single-character string you want
Fortran mode introduces two variables
comment-line-start-skip which play for full-line comments the same
roles played by
ordinary text-following comments. Normally these are set properly by
Fortran mode so you do not need to change them.
The normal Emacs comment command C-x ; has not been redefined. If you use `!' comments, this command can be used with them. Otherwise it is useless in Fortran mode.
The command C-c ; (
fortran-comment-region) turns all the
lines of the region into comments by inserting the string `C$$$' at
the front of each one. With a numeric argument, it turns the region
back into live code by deleting `C$$$' from the front of each line
in it. The string used for these comments can be controlled by setting
fortran-comment-region. Note that here we have an
example of a command and a variable with the same name; these two uses
of the name never conflict because in Lisp and in Emacs it is always
clear from the context which one is meant.