handle EOF correctly in parser and lexer

* module/language/elisp/lexer.scm (lex, get-lexer/1): Return a valid
  token at EOF.
* module/language/elisp/parser.scm (get-expression): Raise an error if
  EOF is reached.
  (read-elisp): If at EOF, return the EOF object instead of attempting
  to read an expression.

module/language/elisp/lexer.scm

@@ -270,7 +270,7 @@
         (c (read-char port)))
     (cond
      ;; End of input must be specially marked to the parser.
-     ((eof-object? c) '*eoi*)
+     ((eof-object? c) (return 'eof c))
      ;; Whitespace, just skip it.
      ((char-whitespace? c) (lex port))
      ;; The dot is only the one for dotted lists if followed by
@@ -390,7 +390,7 @@
         (paren-level 0))
     (lambda ()
       (if finished
-          '*eoi*
+          (cons 'eof ((@ (rnrs io ports) eof-object)))
           (let ((next (lex))
                 (quotation #f))
             (case (car next)

module/language/elisp/parser.scm

@@ -178,6 +178,8 @@
                         (source-properties token)))
                    result)))
     (case type
+      ((eof)
+       (parse-error token "end of file during parsing"))
       ((integer float symbol character string)
        (return (cdr token)))
       ((quote backquote unquote unquote-splicing)
@@ -207,6 +209,9 @@
   (with-fluids ((circular-definitions (make-circular-definitions)))
     (let* ((lexer (get-lexer port))
            (lexbuf (make-lexer-buffer lexer))
-           (result (get-expression lexbuf)))
+           (next (lexbuf 'peek)))
+      (if (eq? (car next) 'eof)
+          (cdr next)
+          (let ((result (get-expression lexbuf)))
             (lexbuf 'finish)
-      result)))
+            result)))))