The usual Emacs comment commands assume that a comment can follow a line of code. In Fortran 77, 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 the Fortran 90 comment syntax where
comments start with ‘!’ and can follow other text. Because only
some Fortran 77 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
fortran-comment-line-start to ‘"!"’.
If you use an unusual value, you may need to change
M-; in Fortran mode runs the standard
This recognizes any kind of existing comment and aligns its text
appropriately; if there is no existing comment, a comment is inserted
and aligned. Inserting and aligning comments are not the same in
Fortran mode as in other modes.
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 indentation is
fortran-minimum-statement-indent-tab for tab format
continuation line style and
for fixed form 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
Compiler directive lines, or preprocessor lines, have much the same
appearance as comment lines. It is important, though, that such lines
never be indented at all, no matter what the value of
fortran-comment-indent-style. The variable
fortran-directive-re is a regular expression that specifies which
lines are directives. Matching lines are never indented, and receive
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.