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(in-package #:lex)
(define-condition lexer-error (error)
((message :initarg :message
:initform nil
:reader message))
(:report (lambda (condition stream)
(format stream "~A" (message condition))))
(:documentation "Dedicated error for an invalid lex."))
(defun file->tokens (file)
"Opens FILE and parses returns a list of tokens, or
NIL if the file could not be opened."
(defun read-instr (lst tokens-so-far)
"Collects tokens in FILE into TOKENS-SO-FAR, splitting on a newline."
(let ((token (read-token)))
(cond ((null token) (reverse tokens-so-far))
((eq token 'nl)
(cons (reverse tokens-so-far) (read-instr nil nil)))
(t (read-instr lst (cons token tokens-so-far))))))
(and (probe-file file)
(with-open-file (*standard-input* file :direction :input)
(remove nil (read-instr '() '())))))
(defun read-token ()
"Reads *STANDARD-INPUT* and returns a token, or nil if the end
of file has been reached.
Whitespace, commas, colons, and parentheses are token delimiters.
Comments start with a semi-colon ';' and all tokens after are ignored."
(let ((chr (read-char *standard-input* nil)))
(cond
((null chr) chr)
((char= chr #\linefeed) 'nl)
((whitespace-char-p chr)
(read-token))
((char= chr #\;)
(progn (read-line *standard-input* nil)
'nl))
((char= chr #\() 'left-paren)
((char= chr #\)) 'right-paren)
((char= chr #\:) 'colon)
((char= chr #\$) 'dollar)
((char= chr #\+) 'plus)
((char= chr #\-) 'minus)
((digit-char-p chr)
(read-immediate chr))
((alpha-char-p chr)
(read-keyword chr))
(t (error 'lexer-error
:message
(format nil "LEX failled--~a is not a valid lexical symbol.~%" chr))))))
(defun read-immediate (chr)
"Reads a sequence of digits, in base 2, 8, 10, or 16.. Throws
`invalid-immediate-or-keyword' error if an alphabetic character is encountered."
;; may be combined with read-keyword-helper
(defun read-immediate-helper (chrs-so-far)
(let ((chr (peek-char nil *standard-input* nil)))
(cond ((and (not (null chr)) (digit-char-p chr))
(read-immediate-helper (cons (read-char *standard-input* nil) chrs-so-far)))
((and (not (null chr)) (alpha-char-p chr))
(error 'lexer-error
:message
(format nil "LEX failed--encountered ~a while reading immediate.~%" chr)))
(t (reverse chrs-so-far)))))
(let* ((next (peek-char nil *standard-input* nil))
(radix (cond ((null next) 10)
((char= next #\b) 2)
((char= next #\o) 8)
((char= next #\x) 16)
((alpha-char-p next) nil)
(t 10)))
(arg (list chr)))
(when (and (char= chr #\0) radix (not (= radix 10)))
(read-char *standard-input* nil)
(setq arg '()))
(parse-integer (coerce (read-immediate-helper arg) 'string) :radix radix)))
(defun read-keyword (chr)
"Reads a sequence of alphabetic characters. Throws `invalid-immediate-or-keyword'
error if a digit is encountered."
;; may be combined with read-immediate-helper
(defun read-keyword-helper (chrs-so-far)
(let ((chr (peek-char nil *standard-input* nil)))
(cond ((and (not (null chr)) (alpha-char-p chr))
(read-keyword-helper (cons (read-char *standard-input* nil) chrs-so-far)))
((and (not (null chr)) (digit-char-p chr))
(error 'lexer-error
:message
(format nil "LEX failed--encountered ~a while reading keyword.~%" chr)))
(t (reverse chrs-so-far)))))
(coerce (read-keyword-helper (list chr)) 'string))
(defun whitespace-char-p (x)
(or (char= #\space x)
(not (graphic-char-p x))))
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