More reasonable..
On Oct 27, 7:15 am, Stuart Halloway <stuart.hallo...@gmail.com> wrote:
> > checking out the "Try Clojure":
>
> > if you type the following, you get output that matches what you typed
> > in every case except for lists.
>
> > Vectors: --> [1 2 3 4]
> > [1 2 3 4]
>
> > Maps: --> {:foo "bar" 3 4}
> > {:foo "bar" 3 4}
>
> > Lists: --> '(1 2 3 4)
> > (1 2 3 4) <----- *INCONSISTENT* why not render this as '(1 2 3 4) ...
> > this would make much more sense to newbies.
>
> > Sets: --> #{1 2 3 4}
> > #{1 2 3 4}
>
> This is an interesting question. Consistency is important, but consistency
> with what? Your mental model for what happens at the REPL needs to keep the
> R, E, and P steps clearly separate.
>
> Working backward: the P (Print) prints things in a way that they can be read
> back, where possible:
>
> (read-string "[1 2 3 4]")
> => [1 2 3 4]
>
> (read-string "(1 2 3 4)")
> => (1 2 3 4)
>
> (read-string "#{1 2 3 4}")
> => #{1 2 3 4}
>
> (read-string "{1 2 3 4}")
> => {1 2, 3 4}
>
> If the P part of the REPL put a tick in front of lists, they would not read
> back correctly:
>
> (read-string "'(1 2 3 4)")
> => (quote (1 2 3 4)) <---- INCONSISTENT
>
> Now to the R (Reader) part. If, as you suggest, the tick were part of the
> reader syntax for lists, you could "fix" the inconsistency above:
>
> ;; hypothetical Clojure with '(...) list literals
> (read-string "' '(1 2 3 4)")
> => (1 2 3 4)
>
> Finally, consider the poor E (Evaluator) in this scenario. The evaluator
> must (1) evaluate lists except (2) *not* evaluate lists that are protected by
> quote. But now that the tick is part of the syntax you have two challenges:
>
> (1) Since the tick no longer prevents evaluation, you have to spell out the
> quote (and still use the tick!)
>
> ;; hypothetical literal list
> (quote '(1 2 3))
>
> (2) Since the tick is required as part of list syntax, your programs have to
> be written with ticks everywhere like this:
>
> '(defn hello-world
> []
> '(println "hello")
>
> You have to understand R, E and P as separate steps to understand the REPL.
>
> As a side note, it is worth mentioning that the REPL is composed of three
> simple parts, and that interactive shells that do not have this factoring are
> much less useful. Imagine if your language didn't separate reading and
> evaluating. You would need JSON or something to serialize data...
>
> Stu
>
> Stuart Halloway
> Clojure/corehttp://clojure.com
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