Sum-partial-def gets the original + definition because it is evaluated
first, if you want late binding, try (partial reduce (var +)).

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On Dec 1, 2016 4:05 PM, "Matthew Hamrick" <matthewjhamr...@gmail.com> wrote:
> I'm confused by the following code.
> Could someone explain to me why the def-ed partial has different behavior
> to the letted one?
> This is especially confusing to me since the #() special form one works as
> I expect.
>
> (def sum-partial-def (partial reduce +))
>
> (let [sum-partial (partial reduce +)
> sum-# #(reduce + %1)
> nums [1 2 3 4]]
> [(sum-partial-def nums)
> (reduce + nums)
> (sum-# nums)
> (sum-partial nums)]) ;; => [10 10 10 10]
>
> (with-redefs [+ (fn [a b]
> (.add (.add (BigInteger. (str a))
> (BigInteger. (str b)))
> (BigInteger/ONE)))]
> (let [sum-partial (partial reduce +)
> sum-# #(reduce + %1)
> nums [1 2 3 4]]
> [(sum-partial-def nums)
> (reduce + nums)
> (sum-# nums)
> (sum-partial nums)])) ;; => [10 13 13 13]
>
> Thanks,
> Matt
>
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