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;; —————————————————————————————————————
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;; PACKAGE
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(defpackage :bf-aheago
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(:use :cl :anaphora)
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(:export :interpret)
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(:nicknames :bf-a))
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(in-package :bf-aheago)
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;; —————————————————————————————————————
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;; MACROS
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(defmacro interpret-char (char)
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`(progn
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(when debug-p (format *error-output* "~A" ,char))
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(cond
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((eq ,char #\.) (output-cell tape pointer))
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((eq ,char #\,) (input-cell tape pointer))
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((eq ,char #\<) (bound-decf pointer tape-length))
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((eq ,char #\>) (bound-incf pointer tape-length))
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((eq ,char #\+) (inc-cell tape pointer))
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((eq ,char #\-) (dec-cell tape pointer))
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((eq ,char #\[) (loop-advance tape pointer input-stream))
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((eq ,char #\]) (loop-rewind tape pointer input-stream)))))
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;; VARYING [NUMBER] [NUMBER] → NUMBER
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(defmacro bound-incf (object &optional (max 256) (min 0))
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"Increment (destructive) an object, but bounds-check with #'bound-ensure."
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`(setf ,object (bound-ensure (1+ ,object) ,max ,min)))
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;; VARYING [NUMBER] [NUMBER] → NUMBER
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(defmacro bound-decf (object &optional (max 256) (min 0))
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"Decrement (destructive) an object, but bounds-check with #'bound-ensure."
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`(setf ,object (bound-ensure (1- ,object) ,max ,min)))
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;; —————————————————————————————————————
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;; INTERPRETER
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;; STREAM → ARRAY
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(defmethod interpret ((input-stream stream) &key (tape-length 30000) (debug-p nil))
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"Interpret the brainfuck code within the given stream: returns the tape."
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(let ((tape (make-tape tape-length))
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(pointer 0))
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(loop :if (not (listen input-stream))
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:return tape
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:do (alet (read-char input-stream)
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(interpret-char it)))))
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(defmethod interpret ((string string) &key (tape-length 30000) (debug-p nil))
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(interpret (make-input-string string) :tape-length tape-length :debug-p debug-p))
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(defmethod interpret ((pathname pathname) &key (tape-length 30000) (debug-p nil))
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(with-open-file (stream pathname)
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(interpret stream :tape-length tape-length :debug-p debug-p)))
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;; —————————————————————————————————————
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;; CELLS
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;; ARRAY NUMBER → NUMBER
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(defun inc-cell (tape index)
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"Increment the given cell."
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(bound-incf (aref tape index)))
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; (setf (aref tape index) (bound-ensure (1+ (aref tape index)))))
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;; ARRAY NUMBER → NUMBENR
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(defun dec-cell (tape index)
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"Decrement the given cell."
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(bound-decf (aref tape index)))
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; (setf (aref tape index) (bound-ensure (1- (aref tape index)))))
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;; ARRAY NUMBER → NIL
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(defun output-cell (tape index)
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"Print the given cell in the tape to stdout."
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(format t "~A" (code-char (aref tape index))))
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;; ARRAY NUMBER → CHAR
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(defun input-cell (tape index)
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"Input a char's int into the tape at given index."
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(alet (read-char *standard-input* nil 0)
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(setf (aref tape index) (if (numberp it) it (char-code it)))))
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;; [NUMBER] → ARRAY
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(defun make-tape (&optional (length 30000))
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"Make a clean, 0-initialized BF tape."
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(make-array (list length) :initial-element 0))
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;; —————————————————————————————————————
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;; LOOPING []
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;; ARRAY NUMBER STREAM → NIL
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(defun loop-rewind (tape index stream)
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"Restart the loop (move pointer to last '[') if nonzero cell value."
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(if (not (zerop (aref tape index)))
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(stream-rewind-to stream #\[)))
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;; ARRAY NUMBER STREAM → NIL
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(defun loop-advance (tape index stream)
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"Skip the loop (move to next ']') if cell value is zero."
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(if (zerop (aref tape index))
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(stream-advance-to stream #\])))
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;; —————————————————————————————————————
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;; STREAM MANIP
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;; STREAM → CHAR
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(defun retroread-char (stream)
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"Read the previous character in a file-stream."
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(alet (file-position stream)
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(file-position stream (- it 2)))
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(read-char stream))
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;; STREAM CHAR → NIL
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(defun stream-advance-to (stream char)
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"Advance a stream's pointer until the given character is read."
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(if (not (eq char (read-char stream)))
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(stream-advance-to stream char)))
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;; STREAM CHAR → NIL
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(defun stream-rewind-to (stream char)
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"Reverse a stream's pointer until the given character is read."
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(if (not (eq char (retroread-char stream)))
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(stream-rewind-to stream char)))
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;; —————————————————————————————————————
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;; MISC
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;; NUMBER [NUMBER] [NUMBER]
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(defun bound-ensure (number &optional (max 256) (min 0))
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"Ensure the given number remains within the given bounds (with overflow)."
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(cond ((> min number) (bound-ensure (+ number max) max min))
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((< max number) (bound-ensure (- max number) max min))
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(T number)))
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Jaidyn Levesque