;; -*- mode: emacs-lisp -*-

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; This program is free software; you can redistribute it and/or         ;;
;; modify it under the terms of the GNU General Public License as        ;;
;; published by the Free Software Foundation; either version 3, or (at   ;;
;; your option) any later version.                                       ;;
;;                                                                       ;;
;; This program is distributed in the hope that it will be useful, but   ;;
;; WITHOUT ANY WARRANTY; without even the implied warranty of            ;;
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU      ;;
;; General Public License for more details.                              ;;
;;                                                                       ;;
;; You should have received a copy of the GNU General Public License     ;;
;; along with this program. If not, see <http://www.gnu.org/licenses/>.  ;;
;;                                                                       ;;
;; Written by and Copyright (C) Francois Fleuret                         ;;
;; Contact <francois@fleuret.org> for comments & bug reports             ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;; This short scripts performs arithmetic computations in a latex
;; file. It collects variables defined by \fflet{VARNAME}{VALUE}
;; expressions in the latex file, and updates the VALUE in the
;; expressions of the form \ffeval{EXPRESSION}{VALUE}

;; Note that you have to add
;;
;; \newcommand{\fflet}[2]{}
;; \newcommand{\ffeval}[2]{#2}
;;
;; Somewhere in your latex file.
;;
;; EXAMPLE
;; \fflet{X}{12} \fflet{Y}{19 + X * (X + 3)} \ffeval{18 * Y}{}


(defun arithmlatex/eval (expression var-table)
  (let ((nb-loops 0))
    (while (string-match "\\([A-Za-z][A-Za-z0-9_]*\\)" expression)
      (setq nb-loops (1+ nb-loops)
            expression
            (replace-match
             (concat "(" (gethash (sxhash (match-string 1 expression)) var-table) ")")
             t t expression))
      (when (> nb-loops 100) (error "Too many evaluation levels"))
      ))
    (calc-eval expression))

(defun arithmlatex (&optional universal) (interactive "P")
  (let ((var-table (make-hash-table))
        (nb-changes 0))

    (save-excursion

      ;; First we collect the variable definitions
      (goto-char (point-min))
      (while (re-search-forward
              "\\fflet{\\([^}]*\\)}{\\([^}]*\\)}"
              nil t)
        (let ((a (match-string-no-properties 1))
              (b (match-string-no-properties 2)))
          (if (gethash (sxhash a) var-table)
              (error "%s is multiply defined" a))
          (puthash (sxhash a) b var-table)
          ))

      ;; Then we evaluate the expressions
      (goto-char (point-min))
      (while (re-search-forward
              "\\ffeval{\\([^}]*\\)}{\\([^}]*\\)}"
              nil t)
        (let* ((a (match-string-no-properties 1))
               (b (match-string-no-properties 2))
               (start (match-beginning 2))
               (end (match-end 2))
               (v (condition-case nil (arithmlatex/eval a var-table) (error "???"))))
          (if (not (stringp v)) (setq v "???"))

          ;; Do the change only if necessary
          (unless (string= v b)
            (setq nb-changes (1+ nb-changes))
            (unless universal
              (kill-region start end)
              (backward-char)
              (insert v)))
          ))
      )

    (if universal
        (message "There would be %s substitutions" nb-changes)
      (message "There have been %s substitutions" nb-changes))
    )
  )