lex quotation marks correctly

brag/examples/quotation-marks.rkt

@@ -0,0 +1,2 @@
+#lang brag
+start: "a" "\"" "'" 'a' '"' '\''

brag/rules/lexer.rkt

@@ -40,6 +40,7 @@
         (:* (:or "\\'" "\\n" "\\t" (:~ "'" "\\")))
         "'")
     (token-LIT (case lexeme
+                 [("'\\''") "\"'\""]
                  [("'\\n'") "'\n'"]
                  [("'\\t'") "'\t'"]
                  [else lexeme]))]
@@ -47,6 +48,7 @@
         (:* (:or "\\\"" "\\n" "\\t" (:~ "\"" "\\")))
         "\"")
     (token-LIT (case lexeme
+                 [("\"\\\"\"") "\"\"\""]
                  [("\"\\n\"") "\"\n\""]
                  [("\"\\t\"") "\"\t\""]
                  [else lexeme]))]

brag/test/test-all.rkt

@@ -13,6 +13,7 @@
          "test-lexer.rkt"
          "test-old-token.rkt"
          "test-parser.rkt"
+         "test-quotation-marks.rkt"
          "test-simple-arithmetic-grammar.rkt"
          "test-simple-line-drawing.rkt"
          "test-weird-grammar.rkt"

brag/test/test-quotation-marks.rkt

@@ -0,0 +1,6 @@
+#lang racket/base
+(require brag/examples/quotation-marks
+         brag/support
+         rackunit)
+
+(check-equal? (parse-tree "a\"'a\"'") '(start "a" "\"" "'" "a" "\"" "'"))