> Of course you have to "evaluate" to know that, but you also have to
evaluate "2" in the same way to know what it means.
I think you're missing the point. 2 is literal because you read it, eval
it, print it, and 2 (the result of evaluation) as printed is the same as
the original input. A function is read, eval'd, printed and is *not* the
same as what was read in. E.g {:a +} => {:a #function[clojure.core/+]}
Literals can be persisted to strings and read back in with no problem,
whereas non-literals can't.
On Wed, Jul 18, 2018 at 12:19 PM Gregg Reynolds <d...@mobileink.com> wrote:
>
>
> On Wed, Jul 18, 2018, 1:55 PM James Reeves <ja...@booleanknot.com> wrote:
>
>> On Wed, 18 Jul 2018 at 19:38, Gregg Reynolds <d...@mobileink.com> wrote:
>>
>>>
>>> On Tue, Jul 17, 2018, 4:11 PM James Reeves <ja...@booleanknot.com>
>>> wrote:
>>>
>>>>
>>>> A data literal evaluates to itself. So for example, `2` is a literal,
>>>> because we only need to read it to know its value, whereas `(+ 1 1)`
>>>> isn't a literal, because we also need to evaluate it to work out the value.
>>>>
>>>
>>> Fair enough. But by that definition function expressions are also
>>> literals.
>>>
>>
>> Not at all:
>>
>> user=> (defn literal? [s] (let [e (read-string s)] (= e (eval e))))
>> #'user/literal?
>> user=> (literal? "2")
>> true
>> user=> (literal? "(fn [x] x)")
>> false
>> user=> (literal? "#(%)")
>> false
>> user=> (literal? "+")
>> false
>>
>> Function expressions don't evaluate to themselves.
>>
>
> To me that means either the definition is wrong or your literal? is
> rigged. Probably the latter; "literal" is meta, it can't be in the language.
>
> Look at it this way: the meaning ("value") of "lambda x.x+1" is just the
> function that increments its arg. Of course you have to "evaluate" to know
> that, but you also have to evaluate "2" in the same way to know what it
> means. Meaning "reduce", and neither form can be further reduced.
>
> Anyway my point is that clojure, like lisp, is a form of the lambda
> calculus, where everything is a function, even the Nats like 2. To me at
> least that is one of the most important lessons of functional programming.
> Ymmv.
>
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