On Oct 15, 2012, at 2:42 PM, Ben Smith-Mannschott wrote:
>
> I think you're confusing:
>
> (eval (list '(fn [x] x) 1))
>
> with:
>
> (eval (list (fn [x] x) 1))
>
> In both cases, eval is being passed a list of two items. The first
> element of the list differs, however:
>
> In the first case, it is a list beginning with the special form fn: a
> function literal that has not yet been evaluated. Eval will have no
> trouble with this.
>
> In the second case it is a reference to an object implementing the
> clojure.lang.IFn interface. That's not a function literal, it's the
> result of evaluating one. This, as you've discovered, may or may not
> work with eval.
>
> If the distinction I'm trying to make is not clear to you, I'd suggest
> having a look at http://www.infoq.com/presentations/Clojure-Macros (It
> does a good job exploring these kinds of distinctions as it's vital to
> have an accurate mental model of how Clojure is evaluated if one
> intends to write macros.)
Ah -- thanks Ben. You are right -- I was confused. FWIW the stuff that I
sometimes do is:
(let [value-function (eval (list 'fn '[x] individual))]
.... bunch of stuff including a call to value-function on an input ...)
Yes, that's your first case, which the OPs example was not.
-Lee
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