On Wed, Jul 27, 2011 at 8:25 PM, Sean Corfield <seancorfi...@gmail.com> wrote:
> On Wed, Jul 27, 2011 at 4:32 PM, Ken Wesson <kwess...@gmail.com> wrote:
>> => (.format (java.util.Formatter.) "%d" (into-array Object [(bigint 2)]))
>> #<Formatter 2>
>>
>> (2N isn't recognized as a BigInteger literal by Clojure 1.2, it seems.)
>>
>> In my copy of Clojure 1.2, format also seems to work:
>>
>> => (format "%d" (bigint 2))
>> "2"
>
> In Clojure 1.2:
>
> (type (bigint 2)) => java.math.BigInteger
>
> In Clojure 1.3:
>
> (type (bigint 2)) => clojure.lang.BigInt
> (type 2N) => clojure.lang.BigInt
What the devil? Why was this done? Seems like wheel reinvention to me.
And format should account for it. A simple change will do it:
(defn format
"Formats a string using java.lang.String.format, see
java.util.Formatter for format
string syntax"
{:added "1.0"
:static true}
^String [fmt & args]
(String/format fmt (to-array (map fixup args))))
where
(defn fixup [o]
(cond
(instance? clojure.lang.BigInt o) (.toBigInteger o)
...
:else o))
Of course, this suggests a generalization of condp:
(defn replace [rmap coll]
(let [s (map #(if-let [[_ v] (find rmap %)] v %) coll)]
(if (seq? coll)
s
(into (empty coll) s))))
(defmacro condx [symb expr & clauses]
(let [default (if (odd? (count clauses)) [:else (last clauses)] [])]
`(cond
~@(mapcat
(fn [[v x]]
[(replace {symb v} expr) x])
(partition 2 clauses))
~@default)))
(defn fixup [o]
(condx class (instance? class o)
clojure.lang.BigInt (.toBigInteger o)
...
o))
Of course, full flexibility might warrant a multimethod for fixup so
that format can be extended to any type. Format tends to occur in I/O
bound code so the runtime overhead of multimethods is probably
acceptable -- indeed, the pprint contrib library already employs them
in a very similar role.
--
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Master: Your father's Lisp REPL. This is the language of a true
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civilized age.
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