support backslashes in patterns

brag/examples/quotation-marks-and-backslashes.rkt

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

brag/examples/quotation-marks.rkt

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

brag/rules/lexer.rkt

@@ -36,7 +36,7 @@
 
 (define (unescape-lexeme lexeme quote-char)
   ;; convert the literal string representation back into an escape char with lookup table
-  (define unescapes (hash "a" 7 "b" 8 "t" 9 "n" 10 "v" 11 "f" 12 "r" 13 "e" 27 "\"" 34 "'" 39))
+  (define unescapes (hash "a" 7 "b" 8 "t" 9 "n" 10 "v" 11 "f" 12 "r" 13 "e" 27 "\"" 34 "'" 39 "\\" 92))
   (define pat (regexp (format "(?<=^~a\\\\).(?=~a$)" quote-char quote-char)))
   (cond
     [(regexp-match pat lexeme)
@@ -49,11 +49,11 @@
    ;; handle whitespace & escape chars within quotes as literal tokens: "\n" "\t" '\n' '\t'
    ;; match the escaped version, and then unescape them before they become token-LITs
    [(:: "'"
-        (:* (:or "\\'" esc-chars (:~ "'" "\\")))
+        (:or (:* (:or "\\'" esc-chars (:~ "'" "\\"))) "\\\\")
         "'")
     (token-LIT (unescape-lexeme lexeme #\'))]
    [(:: "\""
-        (:* (:or "\\\"" esc-chars (:~ "\"" "\\")))
+        (:or (:* (:or "\\\"" esc-chars (:~ "\"" "\\"))) "\\\\")
         "\"")
     (token-LIT (unescape-lexeme lexeme #\"))]
    ["("

brag/test/test-quotation-marks-and-backslashes.rkt

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

brag/test/test-quotation-marks.rkt

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