There it is, corrected:
(in-ns 'clojure.core)
(defmacro with-open
"bindings => [name init ...]
Evaluates body in a try expression with names bound to the values
of the inits, and a finally clause that calls (.close name) on each
name in reverse order."
{:added "1.0"}
[bindings & body]
(assert-args with-open
(vector? bindings) "a vector for its binding"
(even? (count bindings)) "an even number of forms in binding vector")
(cond
(= (count bindings) 0) `(do ~@body)
(symbol? (bindings 0)) `(let ~(subvec bindings 0 2)
(let [res# (try
(with-open ~(subvec
bindings 2) ~@body)
(catch Throwable t#
(try (. ~(bindings 0)
close) (catch Throwable _)) ; eat close exception
(throw t#)))] ; and
rethrow body exception
(. ~(bindings 0) close)
res#))
:else (throw (IllegalArgumentException.
"with-open only allows Symbols in bindings"))))
2011/1/25 Laurent PETIT <laurent.pe...@gmail.com>:
> of course I missed something :-(
>
> 2011/1/25 Laurent PETIT <laurent.pe...@gmail.com>:
>> 2011/1/25 Ken Wesson <kwess...@gmail.com>:
>>> On Mon, Jan 24, 2011 at 7:32 PM, Laurent PETIT <laurent.pe...@gmail.com>
>>> wrote:
>>>> 2011/1/25 Ken Wesson <kwess...@gmail.com>:
>>>>> Are we generally agreed that we want to preserve the body exception,
>>>>> if any, else the close exception, if any, else the body return value?
>>>>>
>>>>> Then, without further ado:
>>>>>
>>>>> (defmacro with-open2 [binding-exprs & body]
>>>>> (if (> (count binding-exprs) 2)
>>>>> `(with-open2 ~(vec (take 2 binding-exprs))
>>>>> (with-open2 ~(vec (drop 2 binding-exprs))
>>>>> ~@body))
>>>>> (let [[sym expr] binding-exprs]
>>>>> `(let [~sym ~expr
>>>>> res# (try
>>>>> [(do ~@body)]
>>>>> (catch Throwable t# t#))]
>>>>> (if (vector? res#) ; body didn't throw
>>>>> (do
>>>>> (.close ~sym) ; so let close throw
>>>>> (res# 0))
>>>>> (do ; body threw
>>>>> (try (.close ~sym) (catch Throwable _#)) ; eat close exception
>>>>> (throw res#))))))) ; and rethrow body exception
>>>>>
>>>>> user=> (with-open [x (Foo.)] (doit x))
>>>>> #<CompilerException java.lang.Exception: close exception
>>>>> (NO_SOURCE_FILE:242)>
>>>>> user=> (with-open2 [x (Foo.)] (doit x))
>>>>> #<CompilerException java.lang.Exception: doit exception
>>>>> (NO_SOURCE_FILE:40)>
>>>>
>>>> What about starting from the current definition of with-open in
>>>> clojure.core, improving upon it (and at the same time, not building
>>>> intermediate wrapper vector) :
>>>>
>>>> (in-ns 'clojure.core)
>>>> (defmacro with-open
>>>> "bindings => [name init ...]
>>>>
>>>> Evaluates body in a try expression with names bound to the values
>>>> of the inits, and a finally clause that calls (.close name) on each
>>>> name in reverse order."
>>>> {:added "1.0"}
>>>> [bindings & body]
>>>> (assert-args with-open
>>>> (vector? bindings) "a vector for its binding"
>>>> (even? (count bindings)) "an even number of forms in binding vector")
>>>> (cond
>>>> (= (count bindings) 0) `(do ~@body)
>>>> (symbol? (bindings 0)) `(let ~(subvec bindings 0 2)
>>>> (try
>>>> (let [res# (with-open ~(subvec
>>>> bindings 2) ~@body)]
>>>> ;body didn't throw
>>>> (. ~(bindings 0) close)
>>>> res#)
>>>> (catch Throwable t#
>>>> (try (. ~(bindings 0) close) (catch
>>>> Throwable _)) ; eat close exception
>>>> (throw t#)))) ; and rethrow body exception
>>>> :else (throw (IllegalArgumentException.
>>>> "with-open only allows Symbols in bindings"))))
>>>
>>> Ah, I guess it may be a bit cleaner to just eschew "finally"
>>> altogether and close in the try and in the catch. The one thing that's
>>> a bit icky about that is that if the body close throws, the catch
>>> clause tries to close the stream again. On the other hand, my
>>> version's vector wrap is a bit icky, perhaps. :)
>>>
>>> Yours works if the binding vector is empty, too; I suppose that's a
>>> good idea. You've also incorporated the core version's error reporting
>>> code. If this makes it into core in any form it should probably
>>> include those features. :)
>>
>> What about this version which gets rid of the double call to close ?
>> Did I miss something (it's getting late here) ?
>>
>> (in-ns 'clojure.core)
>> (defmacro with-open
>> "bindings => [name init ...]
>>
>> Evaluates body in a try expression with names bound to the values
>> of the inits, and a finally clause that calls (.close name) on each
>> name in reverse order."
>> {:added "1.0"}
>> [bindings & body]
>> (assert-args with-open
>> (vector? bindings) "a vector for its binding"
>> (even? (count bindings)) "an even number of forms in binding vector")
>> (cond
>> (= (count bindings) 0) `(do ~@body)
>> (symbol? (bindings 0)) `(let ~(subvec bindings 0 2)
>> (try
>> (with-open ~(subvec bindings 2) ~@body)
>> (catch Throwable t#
>> (try (. ~(bindings 0) close) (catch
>> Throwable _)) ; eat close exception
>> (throw t#))) ; and rethrow body exception
>> (. ~(bindings 0) close))
>> :else (throw (IllegalArgumentException.
>> "with-open only allows Symbols in bindings"))))
>>
>
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