Am Mittwoch, 4. Mai 2016 23:47:07 UTC+2 schrieb Ben Kovitz:
>
> On May 4, 2016, at 5:28 PM, Johannes <bra...@nordakademie.de <javascript:>>
> wrote:
>
> Maybe you are right. But I've deliberately given function objects to eval
> often without any problems until I used functions of some special kind. I
> do not understand why the behavior for the 2 versions of the function f-
> I've shown is different.
>
>
> Oops, I think I missed the main problem: you were passing a pre-evaluated
> map object directly to eval. What eval really wants is the kind of thing
> that the reader returns after it reads a string. The reader doesn’t
> evaluate symbols, like f-. That’s eval’s job. When the reader sees the
> string f-, it returns the symbol f-. You passed eval the actual function
> object, not the symbol f-. Eval wants to see the symbol; it will replace
> it with the object that it evaluates to.
>
> In other words, I think you just forgot to quote the expressions that you
> were passing to eval. Adding the quote, here’s what I get:
>
> user=> (def f- (let [v 1
> #_=> f (fn [x] v)] f))
> #'user/f-
>
> user=> (eval '{:d f-})
> {:d #function[user/fn--10235/f--10236]}
>
> user=> (def f- (let [v 1
> #_=> f (fn [x] x)] f))
> #'user/f-
>
> user=> (eval '{:d f-})
> {:d #function[user/fn--10243/f--10244]}
>
> okay, but why does the following work without quotation?
user> (def f- (let [v 1
f (fn [x] x)] f))
;; => #'user/f-
user> (eval {:d f-})
;; => {:d #function[user/fn--14679/f--14680]}
user>
The problem is that the place in my program where I give the map containing
the function object to eval, the map cannot be quoted.
Johannes
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