Add checks to tagged-handler.

CHANGELOG.md

@@ -7,7 +7,9 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 
 ## [Unreleased]
 
-...
+### Added
+- Add checks to `printer/tagged-handler` to ensure argumenst are a symbol and
+  function, respectively.
 
 ## [1.0.0] - 2015-10-29
 

src/puget/printer.clj

@@ -222,6 +222,14 @@
   "Generates a print handler function which renders a tagged-literal with the
   given tag and a value produced by calling the function."
   [tag value-fn]
+  (when-not (symbol? tag)
+    (throw (ex-info (str "Cannot create tagged handler with non-symbol tag "
+                         (pr-str tag))
+                    {:tag tag, :value-fn value-fn})))
+  (when-not (ifn? value-fn)
+    (throw (ex-info (str "Cannot create tagged handler for " tag
+                         " with non-function value transform")
+                    {:tag tag, :value-fn value-fn})))
   (fn handler
     [printer value]
     (format-doc printer (tagged-literal tag (value-fn value)))))

test/puget/printer_test.clj

@@ -77,6 +77,10 @@
 
 
 (deftest canonical-extensions
+  (testing "tagged-handler construction"
+    (is (thrown? clojure.lang.ExceptionInfo (tagged-handler "foo" str)))
+    (is (thrown? clojure.lang.ExceptionInfo (tagged-handler 'foo "abcd")))
+    (is (ifn? (tagged-handler 'foo str))))
   (let [handlers {java.util.UUID (tagged-handler 'uuid str)}
         printer (canonical-printer handlers)
         uuid-str "31f7dd72-c7f7-4a15-a98b-0f9248d3aaa6"]