On Sun, May 22, 2011 at 6:09 PM, Jason Wolfe <[email protected]> wrote:
> Looks really awesome -- I've been waiting for this since I switched to
> Clojure from CL!
>
> I played around with it a bit, and there are a couple issues that
> prevent it from being usable out of the box for me.
>
> 1. The usual repl entry point is not used, and so, e.g., (set! *warn-
> on-reflection* true) fails.
>
> 2. I could not figure out a way to browse exception chains.
> Typically the "real" stack trace for an exception is reached by
> repeatedly calling .getCause on the exception until the innermost
> exception is reached, but right now I can't see how to access causes
> in the swank-clj debugger. For example try:
>
> (defn foo [x] (map - x))
> (foo (for [x (range 10)] (if (= x 8) "foo" x)))
>
> to see a useless stack trace (in 1.2). I see a couple places in the
> code that deal with causes, so maybe I'm just missing how to access
> them?
Well, if the exception gets bound to *e, you can use this:
(defn pcause
([]
(pcause *e))
([e]
(if-let [c (.getCause e)]
(recur c)
e)))
...
=> (do-something quux mumble 42)
#<Boom!>
=> (pcause)
Exception java.lang.ArithmeticException: divide by zero
at clojure.lang.Numbers.divide (Numbers.java:138)
at com.mycompany.myproject.foo$hairy_calc.invoke (foo.clj:192)
at ... etc.
or something like it.
If it's not getting bound to *e, the above pcause can still be useful with
(defmacro pe [& body]
`(try
~@body
(catch Throwable t (pcause t))))
...
=> (testing-somefn foo 3.141 xyzzy)
#<Kablooey!>
=> (pe (testing-somefn foo 3.141 xyzzy))
Exception java.io.IOException: stream closed
at java.io.FileInputStream.read (FileInputStream.java:177)
at com.mycompany.myproject.bar$some-func.invoke (bar.clj:211)
at ... etc.
=> (defn some-func ... (doall ... ))
#'com.mycompany.myproject.bar/some-func
=> (pe (testing-somefn foo 3.141 xyzzy))
42
=>
Of course, if the exception is being thrown in some other thread, such
as in the evaluation of a pmap or future, all bets are off. Try
temporarily not using the parallelizing construct. In case of failed
Agents, obviously try (pcause (agent-error agnt)).
--
Protege: What is this seething mass of parentheses?!
Master: Your father's Lisp REPL. This is the language of a true
hacker. Not as clumsy or random as C++; a language for a more
civilized age.
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