'alter' expects your anonymous function to take at least one argument (the
current value of the ref being altered), whereas you've passed a 0-arg
function - there's no mention of a '%' so Clojure expands it to:
(fn []
(update-in @v (fnil conj [])))
Indeed, I suspect you want a 2-arg function here - one for the current
value of the ref and one for the number to conj on - if you were writing it
in expanded form you'd write:
(fn [v x]
(update-in v (fnil conj []) x))
Or, in compact form:
#(update-in %1 (fnil conj []) %2)
HTH,
James
On Tuesday, 17 June 2014 19:05:10 UTC+1, Hussein B. wrote:
>
> Thanks, it works.
>
> In case, my initial map is a ref type
>
> (def m (ref { } ))
>
> Why this isn't working?
>
> (dosync
>
> (alter m #(update-in @v [1] (fnil conj [ ])) 11))
>
> On Tuesday, June 17, 2014 7:55:14 PM UTC+2, Mauricio Aldazosa wrote:
>>
>> For updating the value of a map given a key you can use update-in:
>>
>> user> (update-in {1 [11]} [1] conj 22)
>> {1 [11 22]}
>>
>> Now, to handle the case when the key is not present, you can use fnil:
>>
>> user> (update-in {} [1] (fnil conj []) 22)
>> {1 [22]}
>>
>> Cheers,
>> Mauricio
>>
>
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