except.clj: simplify implementation

1 files changed, 24 insertions, 18 deletions

diff --git a/except.clj b/except.clj
index 1fd9c232..e89246cb 100644
--- a/except.clj
+++ b/except.clj
@@ -1,10 +1,10 @@
-;;  Copyright (c) Stephen C. Gilardi. All rights reserved.
-;;  The use and distribution terms for this software are covered by the
-;;  Common Public License 1.0 (http://opensource.org/licenses/cpl.php)
-;;  which can be found in the file CPL.TXT at the root of this distribution.
-;;  By using this software in any fashion, you are agreeing to be bound by
-;;  the terms of this license.
-;;  You must not remove this notice, or any other, from this software.
+;;  Copyright (c) Stephen C. Gilardi. All rights reserved. The use and
+;;  distribution terms for this software are covered by the Common Public
+;;  License 1.0 (http://opensource.org/licenses/cpl.php) which can be found
+;;  in the file CPL.TXT at the root of this distribution. By using this
+;;  software in any fashion, you are agreeing to be bound by the terms of
+;;  this license. You must not remove this notice, or any other, from this
+;;  software.
 ;;
 ;;  except.clj
 ;;
@@ -17,22 +17,28 @@
 (lib/use string)
 
 (defn throw-if
-  "Throws an exception with a message if pred is true.  Arguments are:
-    pred class? format format-args*
-  where class is optional and defaults to Exception, format is a string
-  as documented for java.util.Formatter, and format-args are objects
-  corresponding to format specifiers in format."
+  "Throws an exception with a message if pred is true. Arguments are:
+
+      pred class? format format-args*
+
+  class is optional and defaults to Exception. If present, it must be a
+  Class in the tree under Throwable with a constructor that takes a single
+  String.
+
+  format is a string as documented for java.util.Formatter.
+
+  format-args are zero or more objects that correspond to the format
+  specifiers in format."
   [pred & args]
   (if pred
-    (let [[arg0 arg1 & more] args
-          [class fmt fmt-args] (if (instance? Class arg0)
-                                 [arg0 arg1 more]
-                                 [Exception arg0 (cons arg1 more)])
+    (let [class-present (instance? Class (first args))
+          args (if class-present args (cons Exception args))
+          [class fmt & fmt-args] args
           ctor (.getConstructor (identity class) (into-array [String]))
           message (apply format fmt fmt-args)
           exception (.newInstance ctor (into-array [message]))
           raw-trace (.getStackTrace exception)
           boring? #(not= (.getMethodName %) "doInvoke")
-          trace (drop 2 (drop-while boring? raw-trace))]
-      (.setStackTrace exception (into-array trace))
+          trace (into-array (drop 2 (drop-while boring? raw-trace)))]
+      (.setStackTrace exception trace)
       (throw exception))))