Execute Brain****/Common Lisp: Difference between revisions
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{{implementation|Brainf***}}{{collection|RCBF}}
This is an implementation of [[Brainf***]] written in [[Common Lisp]].
<syntaxhighlight lang="lisp">(defstruct bf-state
(program)
(program-counter 0)
(memory (make-array 1 :initial-element 0 :adjustable t))
(memory-pointer 0
(stack))
(defmacro with-bf-slots ((program-sym program-counter-sym
memory-sym memory-pointer-sym
stack-sym)
obj-expr &body body)
"Macro to replace cumbersome structure slot references with
local lexical macros resembling local variables."
`(
(
(
(,stack-sym
,@body))
(defun adjust-memory (state)
"Modifies memory and memory-pointer such that memory-pointer is
a valid index to the memory array. If it is too large, the array
is extended; if it is negative, the array is extended, its
contents are shifted forward and the memory-pointer is incremented,
by an amount to make the memory ."
(with-bf-slots (program pc mem ptr stack) state
(cond ((>= ptr (length mem))
(adjust-array mem (1+ ptr) :initial-element 0))
((minusp ptr)
(let ((extent (- ptr)))
(incf ptr extent)
(let ((old-memory (copy-seq mem)))
(setf mem (make-array (+ (length old-memory) extent)))
(setf (subseq mem extent) old-memory)))))))
(defun matching-bracket-for (program bracket-index)
(loop with depth
for index
when (>= index (length program))
do (error "unmatched [ bracket")
until (zerop depth)
finally (return index)))
(defun
(with-bf-slots (program pc mem ptr stack) state
(loop while (< pc (length program)) do
(case (aref program pc)
(#\+ (incf (aref mem ptr)))
(#\- (decf (aref mem ptr)))
(#\> (incf ptr) (adjust-memory state))
(#\< (decf ptr) (adjust-memory state))
(#\[ (if (/= 0 (aref mem ptr))
(push (1- pc) stack)
(setf pc (matching-bracket-for program pc))))
(#\] (setf pc (pop stack)))
(#\. (write-char (code-char (aref mem ptr)) stream)))
(incf pc))))
(defun brainfuck-compile-guts (program &optional (start 0) (until-bracket nil))
(loop for insn from start below (length program)
appending (case (aref program insn)
(#\+ `((incf (aref mem ptr))))
(#\- `((decf (aref mem ptr))))
(#\> `((incf ptr) (adjust-memory state)))
(#\< `((decf ptr) (adjust-memory state)))
(#\[ (let ((end (matching-bracket-for program insn)))
(prog1
`((do () ((= 0 (aref mem ptr)))
,@(brainfuck-compile-guts program (1+ insn) end)))
(setf insn end))))
(#\] (if until-bracket
(if (= until-bracket insn)
(loop-finish)
(error "internal problem matching brackets"))
(error "extra ] bracket")))
(#\. `((write-char (code-char (aref mem ptr)) stream))))))
(defun brainfuck-compile (program)
(compile nil `(lambda (&optional (stream *standard-output*))
(let ((state (make-bf-state :program ,program)))
(with-bf-slots (program pc mem ptr stack) state
,@(brainfuck-compile-guts program))
(values)))))
(defun bf (program)
(if (and (not (zerop (length program)))
(char= #\! (aref program 0)))
(funcall (brainfuck-compile program))
(brainfuck-eval (make-bf-state :program program))))
(defun bf-repl ()
"read-eval-print loop for bf. Code prefixed with ! is compiled, otherwise interpreted"
(loop do (fresh-line)
(princ "BRAINFUCK> ")
(bf (read-line))))</
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