;;; -*-scheme-*-

;;; Mes --- Maxwell Equations of Software
;;; Copyright © 2016 Jan Nieuwenhuizen <janneke@gnu.org>
;;;
;;; scm.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-macro (if expr then . else)
  `(cond
    (,expr ,then)
    (#t (cond (,(pair? else) ((lambda () ,@else)))))))

(define-macro (when expr . body)
  `(if ,expr
       ((lambda () ,@body))))

(define (list . rest) rest)

(define (split-params bindings params)
  (cond ((null? bindings) params)
        (#t (split-params (cdr bindings)
                          (append params (cons (caar bindings) '()))))))

(define (split-values bindings values)
  (cond ((null? bindings) values)
        (#t (split-values (cdr bindings)
                          (append values (cdar bindings) '())))))

(define-macro (simple-let bindings rest)
  `((lambda ,(split-params bindings '()) ,@rest)
    ,@(split-values bindings '())))

(define-macro (let-loop label bindings . rest)
  `(let ((,label *unspecified*))
     (let ((,label (lambda ,(split-params bindings '()) ,@rest)))
       (,label ,@(split-values bindings '())))))

(define-macro (let-loop label bindings rest)
  `((lambda (,label)
      (set! ,label (lambda ,(split-params bindings '()) ,@rest))
      (,label ,@(split-values bindings '())))
    *unspecified*))

(define-macro (let bindings-or-label . rest)
  `(cond (,(symbol? bindings-or-label)
          (let-loop ,bindings-or-label ,(car rest) ,(cdr rest)))
         (#t (simple-let ,bindings-or-label ,rest))))

(define-macro (or2 x y)
  `(cond (,x ,x) (#t ,y)))

(define-macro (and2 x y)
  `(cond (,x ,y) (#t #f)))

(define-macro (or . x)
  (cond
   ((null? x) #f)
   ((null? (cdr x)) (car x))
   (#t `(cond (,(car x))
              (#t (or ,@(cdr x)))))))

(define-macro (and . x)
  (cond ((null? x) #t)
        ((null? (cdr x)) (car x))
        (#t `(cond (,(car x) (and ,@(cdr x)))
                   (#t #f)))))

(define (expand-let* bindings body)
  (cond ((null? bindings)
         `((lambda () ,@body)))
        (#t `((lambda (,(caar bindings))
                ,(expand-let* (cdr bindings) body))
              ,@(cdar bindings)))))

(define-macro (let* bindings . body)
  (expand-let* bindings body))

(define (equal? a b) ;; FIXME: only 2 arg
  (cond ((and (null? a) (null? b)) #t)
        ((and (pair? a) (pair? b))
         (and (equal? (car a) (car b))
              (equal? (cdr a) (cdr b))))
        ((and (string? a) (string? b))
         (eq? (string->symbol a) (string->symbol b)))
        ((and (vector? a) (vector? b))
         (equal? (vector->list a) (vector->list b)))
        (#t (eq? a b))))

(define (vector . rest) (list->vector rest))
(define (make-vector n . x)
  (let ((fill (if (pair? x) (cdr x) *unspecified*)))
    (list->vector (let loop ((n n))
                    (if (= 0 n) '()
                        (cons fill (loop (- n 1))))))))

(define (apply f args)
  (eval (cons f args) (current-module)))

(define-macro (defined? x)
  `(assq ,x (cddr (current-module))))

(define (procedure? p)
  (cond ((builtin? p) #t)
        ((and (pair? p) (eq? (car p) 'lambda)))
        ((and (pair? p) (eq? (car p) '*closure*)))
        (#t #f)))

(define (assq-set! alist key val)
  (let ((entry (assq key alist)))
    (cond (entry (set-cdr! entry val)
                 alist)
          (#t (cons (cons key val) alist)))))

(define (assq-ref alist key)
  (let ((entry (assq key alist)))
    (if entry (cdr entry)
        #f)))

(define assv assq)

(define (memq x lst)
  (cond ((null? lst) #f)
        ((eq? x (car lst)) lst)
        (#t (memq x (cdr lst)))))
(define memv memq)

(define (member x lst)
  (cond ((null? lst) #f)
        ((equal? x (car lst)) lst)
        (#t (member x (cdr lst)))))

(define (map f l . r)
  (cond ((null? l) '())
        ((null? r) (cons (f (car l)) (map f (cdr l))))
        ((null? (cdr r))
         (cons (f (car l) (caar r)) (map f (cdr l) (cdar r))))))

(define (identity x) x)
(define (for-each f l . r)
  (apply map (cons f (cons l r)))
  *unspecified*)

(define (not x)
  (cond (x #f)
        (#t #t)))

(define (<= a b) ;; FIXME: only 2 arg
  (or (< a b)
      (= a b)))

(define (>= a b) ;; FIXME: only 2 arg
  (or (> a b)
      (= a b)))

(define (list? x)
  (or (null? x)
      (and (pair? x) (list? (cdr x)))))

(define (unspecified-bindings bindings params)
  (cond ((null? bindings) params)
        (#t (unspecified-bindings
             (cdr bindings)
             (append params (cons (cons (caar bindings) '(*unspecified*)) '()))))))

(define (letrec-setters bindings setters)
  (cond ((null? bindings) setters)
        (#t (letrec-setters (cdr bindings)
                            (append setters
                                    (cons (cons 'set! (car bindings)) '()))))))

(define-macro (letrec bindings . body)
  `(let ,(unspecified-bindings bindings '())
     ,@(letrec-setters bindings '())
     ,@body))

(define gensym
  (let ((counter 0))
    (lambda (. rest)
      (let ((value (number->string counter)))
        (set! counter (+ counter 1))
        (string->symbol (string-append "g" value))))))

;; srfi-1
(define (last-pair lst)
  (let loop ((lst lst))
    (if (or (null? lst) (null? (cdr lst))) lst
        (loop (cdr lst)))))

(define else #t)
(define (unspecific) (if #f #f))