Here is an example of an indentation function:
(defun sample-smie-rules (kind token) (pcase (cons kind token) (`(:elem . basic) sample-indent-basic) (`(,_ . ",") (smie-rule-separator kind)) (`(:after . ":=") sample-indent-basic) (`(:before . ,(or `"begin" `"(" `"{")) (if (smie-rule-hanging-p) (smie-rule-parent))) (`(:before . "if") (and (not (smie-rule-bolp)) (smie-rule-prev-p "else") (smie-rule-parent)))))
A few things to note:
sample-indent-basic
is nil
, then SMIE uses the global
setting smie-indent-basic
. The major mode could have set
smie-indent-basic
buffer-locally instead, but that
is discouraged.
","
make SMIE try to be more clever when
the comma separator is placed at the beginning of lines. It tries to
outdent the separator so as to align the code after the comma; for
example:
x = longfunctionname ( arg1 , arg2 );
":="
exists because otherwise
SMIE would treat ":="
as an infix operator and would align the
right argument with the left one.
"begin"
is an example of the use
of virtual indentation: This rule is used only when "begin"
is
hanging, which can happen only when "begin"
is not at the
beginning of a line. So this is not used when indenting
"begin"
itself but only when indenting something relative to this
"begin"
. Concretely, this rule changes the indentation from:
if x > 0 then begin dosomething(x); end
to
if x > 0 then begin dosomething(x); end
"if"
is similar to the one for
"begin"
, but where the purpose is to treat "else if"
as a single unit, so as to align a sequence of tests rather than indent
each test further to the right. This function does this only in the
case where the "if"
is not placed on a separate line, hence the
smie-rule-bolp
test.
If we know that the "else"
is always aligned with its "if"
and is always at the beginning of a line, we can use a more efficient
rule:
((equal token "if") (and (not (smie-rule-bolp)) (smie-rule-prev-p "else") (save-excursion (sample-smie-backward-token) (cons 'column (current-column)))))
The advantage of this formulation is that it reuses the indentation of
the previous "else"
, rather than going all the way back to the
first "if"
of the sequence.