On 15.02.2009, at 06:26, Chouser wrote:
>
> On Sat, Feb 14, 2009 at 11:32 PM, GS <gsincl...@gmail.com> wrote:
>>
>> On Feb 14, 12:21 pm, Chouser <chou...@gmail.com> wrote:
>>>
>>> (defn count-instances [obj lsts]
>>> (let [instances-in (fn thisfn [lst]
>>> (if (seq lst)
>>> (+ (if (= (first lst) obj) 1 0)
>>> (thisfn (rest lst)))
>>> 0))]
>>> (map instances-in lsts)))
>>
>> Notwithstanding your more idiomatic implementation (snipped),
>> wouldn't
>> "recur" be better than "thisfn"?
>>
>> (defn count-instances [obj lsts]
>> (let [instances-in (fn [lst]
>> (if (seq lst)
>> (+ (if (= (first lst) obj) 1 0)
>> (recur (rest lst)))
>> 0))]
>> (map instances-in lsts)))
>
> Yes, you're absolutely right.
however, the recur isn't in tail position, so it doesn't work:
user=> (defn count-instances [obj lsts]
(let [instances-in (fn [lst]
(if (seq lst)
(+ (if (= (first lst) obj) 1 0)
(recur (rest lst)))
0))]
(map instances-in lsts)))
java.lang.UnsupportedOperationException: Can only recur from tail
position (NO_SOURCE_FILE:12)
all the best,
--Chris
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