;;; ob-calc.el --- Babel Functions for Calc

;; Copyright (C) 2010-2015 Free Software Foundation, Inc.

;; Author: Eric Schulte
;; Keywords: literate programming, reproducible research
;; Homepage: http://orgmode.org

;; This file is part of GNU Emacs.

;; GNU Emacs 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 of the License, or
;; (at your option) any later version.

;; GNU Emacs 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 GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.

;;; Commentary:

;; Org-Babel and Org-Table support for evaluating calc code.
;; See `org-babel-calc-eval' for documentation.

;;; Code:
(require 'ob)
(require 'calc)
(unless (featurep 'xemacs)
  (require 'calc-trail)
  (require 'calc-store))

(declare-function calc-store-into    "calc-store" (&optional var))
(declare-function calc-recall        "calc-store" (&optional var))
(declare-function math-evaluate-expr "calc-ext"   (x))

(defvar org-babel-default-header-args:calc nil
  "Default arguments for evaluating an calc source block.")

(defun org-babel-expand-body:calc (body _params)
  "Expand BODY according to PARAMS, return the expanded body." body)

(defun org-babel-execute:calc (body params)
  "Execute a block of calc code with Babel."
  (org-babel-calc-eval (org-babel-expand-body:calc body params)
		       (org-babel--get-vars params)))

(defvar org--ob-calc-env-symbol nil) ; For org-babel-calc-eval
(defvar org--ob-calc-var-names nil)

(defun org-babel-calc-eval (text &optional environment env-symbol setup env-setup)
  "Evaluate TEXT as set of calc expressions (one per line) and return the top of the stack.

Optional argument ENVIRONMENT is a user-defined variables
environment which is an alist of (SYMBOL . VALUE).

Optional argument ENV-SYMBOL is a symbol of a user-defined
variables environment which is an alist of (SYMBOL . VALUE).

Setting your environment using either of ENVIRONMENT or
ENV-SYMBOL has the same effect. The difference is that this
function caches the value of ENV-SYMBOL internally between
succesive evaluations with ENV-SYMBOL arguments of equal symbol
names and reevaluates the value of ENV-SYMBOL only when the
symbol name of ENV-SYMBOL changes.

Additionally, setting ENV-SYMBOL to nil will forget any
internal environment before applying ENVIRONMENT, i.e. with
ENV-SYMBOL set to nil this function is pure.

You can also use `org-babel-calc-set-env',
`org-babel-calc-reset-env' and `org-babel-calc-store-env' to set,
reset and update the internal environment between evaluations.

Optional argument SETUP allows additional calc setup on every
evaluation.

Optional argument ENV-SETUP allows additional calc setup on every
ENV-SYMBOL change.

This function is useful if you want to evaluate complicated
formulas in a table, e.g. after evaluating

  (setq an-env '((foo . \"2 day\")
                 (bar . \"6 hr\")))

you can use this in the following table

  | Expr      | Result       |
  |-----------+--------------|
  | foo + bar | 2 day + 6 hr |
  | foo - bar | 2 day - 6 hr |
  |-----------+--------------|
  #+TBLFM: $2='(org-babel-calc-eval $1 an-env)

which would become slow to recompute with a lot of rows, but then
you can change the TBLFM line to

  #+TBLFM: $2='(org-babel-calc-eval $1 nil 'an-env)

and it would become fast again.

SETUP argument can be used like this:

  | Expr      | Result   |
  |-----------+----------|
  | foo + bar | 2.25 day |
  | foo - bar | 1.75 day |
  |-----------+----------|
  #+TBLFM: $2='(org-babel-calc-eval $1 nil 'an-env nil (lambda () (calc-units-simplify-mode t)))

In case that is not fast or complicated enough, you can combine
this with `org-babel-calc-store-env' to produce some clever stuff
like, e.g. computing environment on the fly (an-env variable is
not actually used here, it is being generated just in case you
want to use it elsewhere):

  (setq an-env nil)
  (defun compute-and-remember (name expr)
    (let* ((v (org-babel-calc-eval expr nil 'an-env nil (lambda () (calc-units-simplify-mode t))))
           (c `(,(intern name) . ,v)))
        (org-babel-calc-store-env (list c))
        (push c an-env)
        v))

and then

  | Name | Expr       | Value    |
  |------+------------+----------|
  | foo  | 2 day      | 2 day    |
  | bar  | foo + 6 hr | 2.25 day |
  |------+------------+----------|
  #+TBLFM: $3='(compute-and-remember $1 $2)

Note that you can set ENV-SYMBOL to 'nil to get ENV-SETUP
without.

The subsequent results might become somewhat surprising in case
ENVIRONMENT overrides variables set with ENV-SYMBOL."
  (org-babel-calc-init)
  (cond
    ((equal env-symbol nil) (org-babel-calc-reset-env))
    ((not (equal (symbol-name env-symbol) org--ob-calc-env-symbol))
	(org-babel-calc-set-env env-symbol)
	(unless (null env-setup)
	  (funcall env-setup))))
  (org-babel-calc-store-env environment)
  (unless (null setup)
    (funcall setup))
  (org-babel-calc-eval-string text))

(defun org-babel-calc-init ()
  "Initialize calc.

You probably don't want to call this function explicitly."
  (unless (get-buffer "*Calculator*")
    (save-window-excursion (calc) (calc-quit))))

(defun org-babel-calc-set-env (env-symbol)
  "Force update current environment with the value of ENV-SYMBOL.

See `org-babel-calc-eval' for more info."
  (org-babel-calc-reset-env)
  (org-babel-calc-store-env (eval env-symbol))
  (setq org--ob-calc-env-symbol (symbol-name env-symbol)))

(defun org-babel-calc-reset-env ()
  "Forget current environment and the value of the last
ENV-SYMBOL.

See `org-babel-calc-eval' for more info."
  (setq org--ob-calc-var-names nil
	org--ob-calc-env-symbol nil))

(defun org-babel-calc-store-env (vars)
  "Store an environment (alist of (SYMBOL . VALUE) pairs) into calc.

See `org-babel-calc-eval' for more info."
  (mapc
    (lambda (pair)
	(let ((name (symbol-name (car pair)))
	    (value (cdr pair)))
	;; Using symbol-name and then intern here may seem a little
	;; crazy, but without it calc may not recall some of variables
	;; that got non-canonical symbols, which will be very surprising
	;; for users that produce their environments with '(...) syntax.
	;; Better safe than sorry.
	  (calc-store-value (intern name) value "" 0)
	  (push name org--ob-calc-var-names)))
    vars))

(defun org-babel-calc-eval-string (text)
  (mapc #'org-babel-calc-eval-line (split-string text "[\n\r]"))
  (save-excursion
    (with-current-buffer (get-buffer "*Calculator*")
      (calc-eval (calc-top 1)))))

(defun org-babel-calc-eval-line (line)
  (let ((line (org-babel-trim line)))
    (when (> (length line) 0)
	(cond
	 ;; simple variable name
	 ((member line org--ob-calc-var-names) (calc-recall (intern line)))
	 ;; stack operation
	 ((string= "'" (substring line 0 1))
	(funcall (lookup-key calc-mode-map (substring line 1)) nil))
	 ;; complex expression
	 (t (calc-push-list
	 (list (let ((res (calc-eval line)))
		 (cond
		   ((numberp res) res)
		   ((math-read-number res) (math-read-number res))
		   ((listp res) (error "Calc error \"%s\" on input \"%s\""
					 (cadr res) line))
		   (t (replace-regexp-in-string "'" ""
			(calc-eval
			  (math-evaluate-expr
				;; resolve user variables, calc built in
				;; variables are handled automatically
				;; upstream by calc
				(mapcar #'org-babel-calc-maybe-resolve-var
				;; parse line into calc objects
				(car (math-read-exprs line))))))))))))))))

(defun org-babel-calc-maybe-resolve-var (el)
  (if (consp el)
	(if (and (equal 'var (car el))
		 (member (symbol-name (cadr el)) org--ob-calc-var-names))
	  (progn
	    (calc-recall (cadr el))
	    (prog1
	      (calc-top 1)
	      (calc-pop 1)))
	  (mapcar #'org-babel-calc-maybe-resolve-var el))
    el))

(provide 'ob-calc)

;;; ob-calc.el ends here