+
+(defmacro and (&rest forms)
+ (cond
+ ((null forms)
+ t)
+ ((null (cdr forms))
+ (car forms))
+ (t
+ `(if ,(car forms)
+ (and ,@(cdr forms))
+ nil))))
+
+
+(defmacro or (&rest forms)
+ (cond
+ ((null forms)
+ nil)
+ ((null (cdr forms))
+ (car forms))
+ (t
+ `(if ,(car forms)
+ t
+ (or ,@(cdr forms))))))
+
+
+(defmacro prog1 (form &rest body)
+ (let ((value (make-symbol "VALUE")))
+ `(let ((,value ,form))
+ ,@body
+ ,value)))
+
+
+(defun char= (x y) (= x y))
+
+
+;;;; Reader
+
+;;; It is a basic Lisp reader. It does not use advanced stuff
+;;; intentionally, because we want to use it to bootstrap a simple
+;;; Lisp. The main entry point is the function `ls-read', which
+;;; accepts a strings as argument and return the Lisp expression.
+(defun make-string-stream (string)
+ (cons string 0))
+
+(defun %peek-char (stream)
+ (and (< (cdr stream) (length (car stream)))
+ (char (car stream) (cdr stream))))
+
+(defun %read-char (stream)
+ (and (< (cdr stream) (length (car stream)))
+ (prog1 (char (car stream) (cdr stream))
+ (setcdr stream (1+ (cdr stream))))))
+
+(defun whitespacep (ch)
+ (or (char= ch #\space) (char= ch #\newline) (char= ch #\tab)))
+
+(defun skip-whitespaces (stream)
+ (let (ch)
+ (setq ch (%peek-char stream))
+ (while (and ch (whitespacep ch))
+ (%read-char stream)
+ (setq ch (%peek-char stream)))))
+
+(defun terminalp (ch)
+ (or (null ch) (whitespacep ch) (char= #\) ch) (char= #\( ch)))
+
+
+(defun read-until (stream func)
+ (let ((string "")
+ (ch))
+ (setq ch (%peek-char stream))
+ (while (not (funcall func ch))
+ (setq string (concat string (string ch)))
+ (%read-char stream)
+ (setq ch (%peek-char stream)))
+ string))
+
+(defun skip-whitespaces-and-comments (stream)
+ (let (ch)
+ (skip-whitespaces stream)
+ (setq ch (%peek-char stream))
+ (while (and ch (char= ch #\;))
+ (read-until stream (lambda (x) (char= x #\newline)))
+ (skip-whitespaces stream)
+ (setq ch (%peek-char stream)))))
+
+(defun %read-list (stream)
+ (skip-whitespaces-and-comments stream)
+ (let ((ch (%peek-char stream)))
+ (cond
+ ((char= ch #\))
+ (%read-char stream)
+ nil)
+ ((char= ch #\.)
+ (%read-char stream)
+ (skip-whitespaces-and-comments stream)
+ (prog1 (ls-read stream)
+ (unless (char= (%read-char stream) #\))
+ (error "')' was expected."))))
+ (t
+ (cons (ls-read stream) (%read-list stream))))))