;;; -*-scheme-*-

;;; Mes --- Maxwell Equations of Software
;;; Copyright © 2016 Jan Nieuwenhuizen <janneke@gnu.org>
;;;
;;; mes.mes: This file is part of Mes.
;;;
;;; Mes 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.
;;;
;;; Mes 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 Mes.  If not, see <http://www.gnu.org/licenses/>.

;; The Maxwell Equations of Software -- John McCarthy page 13
;; http://www.softwarepreservation.org/projects/LISP/book/LISP%201.5%20Programmers%20Manual.pdf

;; (define (caar x) (car (car x)))
;; (define (cadr x) (car (cdr x)))
;; (define (cdar x) (cdr (car x)))
;; (define (cddr x) (cdr (cdr x)))
;; (define (caadr x) (car (car (cdr x))))
;; (define (caddr x) (car (cdr (cdr x))))
;; (define (cddar x) (cdr (cdr (car x))))
;; (define (cdadr x) (cdr (car (cdr x))))
;; (define (cadar x) (car (cdr (car x))))
;; (define (cdddr x) (cdr (cdr (cdr x))))

;; ;; Page 12
;; (define (pairlis x y a)
;;   ;;(debug "pairlis x=~a y=~a a=~a\n" x y a)
;;   (cond
;;    ((null? x) a)
;;    ((atom? x) (cons (cons x y) a))
;;    (#t (cons (cons (car x) (car y))
;;              (pairlis (cdr x) (cdr y) a)))))

;; (define (assq x a)
;;   ;;(stderr "assq x=~a\n" x)
;;   ;;(debug "assq x=~a a=~a\n" x a)
;;   (cond
;;    ((null? a) #f)
;;    ((eq? (caar a) x) (car a))
;;    (#t (assq x (cdr a)))))

;; ;; Page 13
;; (define (eval-quote fn x)
;;   ;(debug "eval-quote fn=~a x=~a" fn x)
;;   (apply-env fn x '()))

(define (evcon c a)
  ;;(debug "evcon c=~a a=~a\n" c a)
  (cond
   ((null? c) *unspecified*)
   ;; single-statement cond
   ;; ((eval (caar c) a) (eval (cadar c) a))
   ((eval (caar c) a)
    (cond ((null? (cddar c)) (eval (cadar c) a))
          (#t (eval (cadar c) a)
              (evcon
               (cons (cons #t (cddar c)) '())
               a))))
   (#t (evcon (cdr c) a))))

(define (evlis m a)
  ;;(debug "evlis m=~a a=~a\n" m a)
  ;; (display 'mes-evlis:)
  ;; (display m)
  ;; (newline)
  (cond
   ((null? m) '())
   (#t (cons (eval (car m) a) (evlis (cdr m) a)))))


(define (apply-env fn x a) 
  ;; (display 'mes-apply-env:)
  ;; (newline)
  ;; (display 'fn:)
  ;; (display fn)
  ;; (newline)
  ;; (display 'builtin:)
  ;; (display (builtin? fn))
  ;; (newline)
  ;; (display 'x:)
  ;; (display x)
  ;; (newline)
  (cond
   ((atom? fn)
    (cond
     ((eq? fn 'current-module)
      (c:apply-env current-module '() a))
     ((eq? fn 'call-with-values)
      (c:apply-env 'call-with-values x a))
     ((builtin? fn)
      (call fn x))
     (#t (apply-env (eval fn a) x a))))
   ((eq? (car fn) 'lambda)
    (begin-env (cddr fn) (pairlis (cadr fn) x a)))
   ((eq? (car fn) 'label) (apply-env (caddr fn) x (cons (cons (cadr fn)
                                                         (caddr fn)) a)))))

(define (begin-env body a)
  (cond ((null? body) *unspecified*)
        ((null? (cdr body)) (eval (car body) a))
        (#t (eval (car body) a)
            (begin-env (cdr body) a))))

(define (set-env! x e a)
  (set-cdr! (assq x a) e))

(define (eval e a)
  ;;(debug "eval e=~a a=~a\n" e a)
  ;;(debug "eval (atom? ~a)=~a\n" e (atom? e))
  ;; (display 'mes-eval:)
  ;; (display e)
  ;; (newline)
  ;; (display 'a:)
  ;; (display a)
  ;; (newline)
  (cond
   ((eq? e #t) #t)
   ((eq? e #f) #f)
   ((char? e) e)
   ((number? e) e)
   ((string? e) e)
   ((vector? e) e)
   ((atom? e) (cdr (assq e a)))
   ((builtin? e) e)
   ((atom? (car e))
    (cond
     ((eq? (car e) 'quote) (cadr e))
     ((eq? (car e) 'lambda) e)
     ((eq? (car e) 'set!) (set-env! (cadr e) (caddr e) a))
     ((eq? (car e) 'unquote) (eval (cadr e) a))
     ((eq? (car e) 'quasiquote) (eval-quasiquote (cadr e) a))
     ((eq? (car e) 'cond) (evcon (cdr e) a))
     ((pair? (assq (car e) (cdr (assq '*macro* a))))
      (c:eval
       (c:apply-env
        (cdr (assq (car e) (cdr (assq '*macro* a))))
        (cdr e)
        a)
       a))
     (#t (apply-env (car e) (evlis (cdr e) a) a))))
   (#t (apply-env (car e) (evlis (cdr e) a) a))))

(define (eval-quasiquote e a)
  ;; (display 'mes-eval-quasiquote:)
  ;; (display e)
  ;; (newline)
  (cond ((null? e) e)
        ((atom? e) e)
        ((atom? (car e)) (cons (car e) (eval-quasiquote (cdr e) a)))
        ((eq? (caar e) 'unquote) (cons (eval (cadar e) a) '()))
        ((eq? (caar e) 'quote) (cons (cadar e) '()))
        ((eq? (caar e) 'quasiquote) (cons (cadar e) '()))
        (#t (cons (car e) (eval-quasiquote (cdr e) a)))))

;; readenv et al works, but slows down dramatically
(define (DISABLED-readenv a)
  (readword (getchar) '() a))

(define (readword c w a)
  ;; (display 'mes-readword:)
  ;; (display c)
  ;; (newline)
  (cond ((eq? c -1) ;; eof
         (cond ((eq? w '()) '())
               (#t (lookup w a))))
        ((eq? c 10) ;; \n
         (cond ((eq? w '()) (readword (getchar) w a))
               ;; DOT ((eq? w '(*dot*)) (car (readword (getchar) '() a)))
               (#t (lookup w a))))
        ((eq? c 32) ;; \space
         (readword 10 w a))
        ((eq? c 40) ;; (
         (cond ((eq? w '()) (readlist a))
               (#t (ungetchar c) (lookup w a))))
        ((eq? c 41) ;; )
         (cond ((eq? w '()) (ungetchar c) w)
               (#t (ungetchar c) (lookup w a))))
        ((eq? c 39) ;; '
         (cond ((eq? w '())
                (cons (lookup (cons c '()) a)
                      (cons (readword (getchar) w a) '())))
               (#t (ungetchar c) (lookup w a))))
        ((eq? c 59) ;; ;
         (readcomment c)
         (readword 10 w a))
        ((eq? c 35) ;; #
         (cond ((eq? (peekchar) 33) ;; !
                (getchar)
                (readblock (getchar))
                (readword 10 w a))
               ;; TODO: char, vector
               (#t (readword (getchar) (append w (cons c '())) a))))
        (#t (readword (getchar) (append w (cons c '())) a))))

(define (readblock c)
  ;; (display 'mes-readblock:)
  ;; (display c)
  ;; (newline)
  (cond ((eq? c 33) (cond ((eq? (peekchar) 35) (getchar))
                         (#t (readblock (getchar)))))
        (#t (readblock (getchar)))))

(define (eat-whitespace)
  (cond ((eq? (peekchar) 10) (getchar) (eat-whitespace))
        ((eq? (peekchar) 32) (getchar) (eat-whitespace))
        ((eq? (peekchar) 35) (getchar) (eat-whitespace))
        (#t #t)))

(define (readlist a)
  ;; (display 'mes-readlist:)
  ;; (newline)
  (eat-whitespace)
  (cond ((eq? (peekchar) 41) ;; )
         (getchar)
         '())
        ;; TODO *dot*
        (#t (cons (readword (getchar) '() a) (readlist a)))))

(define (readcomment c)
  (cond ((eq? c 10) ;; \n
         c)
        (#t (readcomment (getchar)))))