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• Example-lexer

Lex-punctuation

Match punctuation characters to create a :punctuation token.

Signature

(lex-punctuation sin) → (mv tok sin)

Arguments

sin — The sin stobj.

Returns

tok — A punctuation token taken from the start of the input stream, or nil if the input stream does not start with some valid punctuation.
    Type (equal (token-p tok) (if tok t nil)).

sin — The remaining input stream, with the leading digits removed.

It's important to put the ++ and -- operators first here. For instance, if + came first, then we'd end up converting ++ into two separate + tokens.

Definitions and Theorems

Function: lex-punctuation

(defun lex-punctuation (sin)
  (declare (xargs :stobjs (sin)))
  (declare (xargs :guard t))
  (let ((__function__ 'lex-punctuation))
    (declare (ignorable __function__))
    (b* (((mv match sin)
          (sin-match-some-lit '("++" "--" ";" "+" "-" "*" "/")
                              sin))
         ((unless match) (mv nil sin)))
      (mv (make-token :type :punctuation
                      :text match)
          sin))))

Theorem: return-type-of-lex-punctuation.tok

(defthm return-type-of-lex-punctuation.tok
  (b* (((mv ?tok ?sin) (lex-punctuation sin)))
    (equal (token-p tok) (if tok t nil)))
  :rule-classes :rewrite)

Theorem: lex-punctuation-progress-weak

(defthm lex-punctuation-progress-weak
  (mv-let (tok new-sin)
          (lex-punctuation sin)
    (declare (ignorable tok new-sin))
    (<= (len (strin-left new-sin))
        (len (strin-left sin))))
  :rule-classes ((:rewrite) (:linear)))

Theorem: lex-punctuation-progress-strong

(defthm lex-punctuation-progress-strong
  (mv-let (tok new-sin)
          (lex-punctuation sin)
    (declare (ignorable tok new-sin))
    (implies tok
             (< (len (strin-left new-sin))
                (len (strin-left sin)))))
  :rule-classes ((:rewrite) (:linear)))

Theorem: lex-punctuation-reconstruction

(defthm lex-punctuation-reconstruction
  (b* (((mv tok new-sin)
        (lex-punctuation sin)))
    (implies tok
             (equal (append (explode (token->text tok))
                            (strin-left new-sin))
                    (strin-left sin)))))