Re: SMIE: if-elseif-else constructs

[Andreas Matthias <andreas.matthias@gmail.com>]

Stefan Monnier wrote:
>
> >       (assoc "then" "end")
>
> This says that
>
>     a then b then c then d
>
> is acceptable and that `a`, `b`, and `c` should be considered as
> siblings (i.e. at the same depth level).  Same for `end`.

I see. Using assoc seemed to be the easy way but was not reasonable.

I think I've found a better way. I revised the grammar and adjusted
the indentation rules.
The following seems to work.


(require 'smie)

(setq foobar-grammar
  (smie-prec2->grammar
   (smie-bnf->prec2
    `((insts (insts ";" insts)
             (inst))
      (inst (if))
      (exp)
    (if ("if" if-body1 "end"))
    (if-body1 (exp "then" if-body2))
    (if-body2 (insts "elseif" if-body1)
              (insts "else" insts)
              (insts)))

    '((assoc ";")
      ))))

(defun foobar-rules (kind token)
  (message "rule: (%s . %s) at point %d" kind token (point))
  (pcase (cons kind token)
    (`(:elem . basic) foobar-indent-basic)

    (`(:before . "then") 0)
    (`(:after . "then") foobar-indent-basic)

    (`(:before . "else") 0)
    (`(:after . "else") foobar-indent-basic)

    (`(:before . "elseif") 0)
    (`(:after . "elseif") foobar-indent-basic)
    ))

(setq foobar-indent-basic 4)

(define-derived-mode foobar-mode prog-mode "foobar"
  :syntax-table nil
  (modify-syntax-entry ?/ ". 124")
  (modify-syntax-entry ?* ". 23b")
  (modify-syntax-entry ?\n ">")
  (setq comment-start "//")
  (smie-setup foobar-grammar #'foobar-rules)
  (font-lock-add-keywords
   nil
   `((,(regexp-opt '("if" "then" "elseif" "else" "end")) .
font-lock-keyword-face)))
  (font-lock-mode)
  (font-lock-ensure (point-min) (point-max)))