stricter about line breaks, less finicky about blank statements

beautiful-racket-demo/basic-demo/expander.rkt

@@ -23,7 +23,7 @@
       (define (LINE-NUMBER-ID #:srcloc? [srcloc #f])
         (if srcloc
             (syntax-srcloc #'ORIG-LOC)
-            (begin STATEMENT ...))))))
+            (begin (void) STATEMENT ...))))))
 
 (define b-rem void)
 (define (b-print [val ""]) (displayln val))

beautiful-racket-demo/basic-demo/lexer.rkt

@@ -6,8 +6,9 @@
 (define basic-lexer
   (lexer-srcloc
    [(eof) (return-without-srcloc eof)]
+   [(from/stop-before "rem" "\n") (token 'REM lexeme)]
+   [(:seq "\n" digits) (token 'LINE-NUMBER (string->number (string-trim lexeme)))] 
    [whitespace (token lexeme #:skip? #t)]
-   [(from/to "rem" "\n") (token 'REM lexeme)]
    [(:or "print" "goto" "end" "+" ":") lexeme]
    [digits (token 'INTEGER (string->number lexeme))]
    [(:or (:seq (:? digits) "." digits)

beautiful-racket-demo/basic-demo/parser.rkt

@@ -1,7 +1,7 @@
 #lang brag
 b-program : b-line*
-b-line : @b-line-number b-statement (/":" b-statement)*
-b-line-number : INTEGER
+b-line : @b-line-number [b-statement] (/":" [b-statement])*
+b-line-number : LINE-NUMBER
 @b-statement : b-rem
              | b-print
              | b-goto

beautiful-racket-demo/basic-demo/sample.rkt

@@ -1,5 +1,6 @@
 #lang basic-demo
 30 rem print "ignored"
+35
 50 print "never gets here"
 40 end
 60 print 'three' : print 1.0 + 3