[plt-scheme] A question about external representation

>From the docs of DrScheme, version 3.99.0.9-svn25jan2008 [3m]: "Evaluates 
val-expr and uses the result to select a case-clause. The selected clause is 
the first one with a datum whose quoted form is eqv? to the result of 
val-expr."
And likewise in R6RS: "A case expression is evaluated as follows. <Key> is 
evaluated and its result is compared using eqv? "

Jos Koot

----- Original Message ----- 
From: "Grant Rettke" <grettke at acm.org>
To: "pltscheme" <plt-scheme at list.cs.brown.edu>
Sent: Saturday, January 26, 2008 11:16 PM
Subject: [plt-scheme] A question about external representation


> Today I worked on a problem that involved converting a 'cond'
> expression to 'case.
>
> I was checking for 'value in the cond expression, but in the case I
> should have been checking for unquoted value.
>
> For example:
>
> (define test2
>  (λ (arg)
>    (case arg
>      ([test2] "quote test2")
>      (['test2] "quote quote test2")
>      (else #f))))
>
>> (test2 'test2)
>> (test2 ''test2)
>
> Reading the documentation for case it says that each datum checked for
> equality is "an external representation" of some object.
>
> My question is, when we type (quote value), is the external
> representation whatever shows up in the repl when that is evaluated?
>
> What is external representation?
>


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