more work on errors

src/name/choi/joshua/fnparse.clj

@@ -6,7 +6,8 @@
 ; - If the token sequence is valid, it returns a (0) vector containing the (1) consumed
 ;   symbols' products and (2) a state data object, usually a map. The state contains the (3)
 ;   sequence of remaining tokens, usually with the key *remainder-accessor*.
-; - If the given token sequence is invalid and the rule fails, it simply returns nil.
+; - If the given token sequence is invalid, then the rule Fails, meaning that it either 
+;   simply returns nil or raises an error.
 
 ; - (0) is called the rule's result.
 ; - (1) is called the rule's product.

src/name/choi/joshua/fnparse/json.clj

@@ -75,7 +75,7 @@
 
 (def hexadecimal-digit
   (failpoint (alt decimal-digit (lit-alt-seq "ABCDEF" nb-char-lit))
-    #(raise parse-error %2 "hexadecimal digit expected where \"%s\" is" [(first %1)])))
+    (expectation-error-fn "hexadecimal digit")))
 
 (def unescaped-char (except json-char (alt escape-indicator string-delimiter)))