Re: [racket-users] Case and eof

[Jay McCarthy]

You would want (== eof), because 'eof' is just an identifier, so
you're binding x to eof.

Jay

On Wed, Apr 6, 2016 at 12:05 PM, rom cgb  wrote:
> On Monday, April 4, 2016 at 10:44:46 PM UTC+2, Alex Knauth wrote:
>> I'm convinced that implicit quotes are the root of almost all evil in lisp 
>> programming languages. That's a big reason why I like the teaching languages 
>> better in terms of things making sense.
>>
>> It's also why I normally use `match` instead of `case` even when I *am* 
>> dealing with integers or symbols.
>
> How to use eof with match ?
>
> For example, with
>
> (define (test x)
> (match x [1   "one"]
>  [2   "two"]
>  [eof "eof"]
>  [3   "three"]))
>
> Why (test 3) evaluates to "eof", not "three" ?
>



-- 
Jay McCarthy
Associate Professor
PLT @ CS @ UMass Lowell
http://jeapostrophe.github.io

   "Wherefore, be not weary in well-doing,
  for ye are laying the foundation of a great work.
And out of small things proceedeth that which is great."
  - D 64:33

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Re: [racket-users] Case and eof

[rom cgb]

On Monday, April 4, 2016 at 10:44:46 PM UTC+2, Alex Knauth wrote:
> I'm convinced that implicit quotes are the root of almost all evil in lisp 
> programming languages. That's a big reason why I like the teaching languages 
> better in terms of things making sense.
> 
> It's also why I normally use `match` instead of `case` even when I *am* 
> dealing with integers or symbols.

How to use eof with match ?

For example, with

(define (test x) 
(match x [1   "one"] 
 [2   "two"] 
 [eof "eof"] 
 [3   "three"]))

Why (test 3) evaluates to "eof", not "three" ?

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Re: [racket-users] Case and eof

[Jon Zeppieri]

On Mon, Apr 4, 2016 at 3:40 PM, Jay McCarthy  wrote:

> case is just for integers and symbols.
>


I'm not sure if you meant this as a claim about how you think `case` should
be used, but it certainly does work for more than just integers and
symbols. It will work for any data with a literal reader syntax. -J

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Re: [racket-users] Case and eof

[Alex Knauth]

> On Apr 4, 2016, at 3:40 PM, Jay McCarthy  wrote:

> (member eof '(eof)) is #f
> 
> Because '(eof) is the same as (list 'eof) NOT (list eof)
> 
> Jay

I'm convinced that implicit quotes are the root of almost all evil in lisp 
programming languages. That's a big reason why I like the teaching languages 
better in terms of things making sense.

It's also why I normally use `match` instead of `case` even when I *am* dealing 
with integers or symbols.

Alex Knauth

> On Mon, Apr 4, 2016 at 3:34 PM, rom cgb  wrote:
>> Hi,
>> 
>> Trying to use eof in a case expression but it doesn't work.
>> 
>> For example
>> 
>>(define (test x)
>>  (case x
>>[(eof) eof]
>>[else  "else"]))
>> 
>> 
>> (test eof) will then evaluate to "else" despite (equal? eof eof) evaluating 
>> to #t.
>> 
>> Why ?

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Re: [racket-users] Case and eof

[Jens Axel Søgaard]

2016-04-04 21:34 GMT+02:00 rom cgb :

> Hi,
>
> Trying to use eof in a case expression but it doesn't work.
>
> For example
>
> (define (test x)
>   (case x
> [(eof) eof]
> [else  "else"]))
>
>
> (test eof) will then evaluate to "else" despite (equal? eof eof)
> evaluating to #t.
>
> Why ?


The (eof) clause in case is a list of datums. That means case
will taste for the symbol eof and not the end of file object.

(case 'eof
  [(eof) 42])   ; 42

(case eof
  [(eof) 42]
  [else  #f])  ; #f

Instead use cond
  (cond
[(eof-object? x) ...]
[else  #f])

/Jens Axel





>
>
>
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Re: [racket-users] Case and eof

[Jay McCarthy]

case is just for integers and symbols.

(case x [(eof) eof] [else "else"])

is equivalent to

(cond [(member x '(eof)) eof] [else "else"])

and

(member eof '(eof)) is #f

Because '(eof) is the same as (list 'eof) NOT (list eof)

Jay


On Mon, Apr 4, 2016 at 3:34 PM, rom cgb  wrote:
> Hi,
>
> Trying to use eof in a case expression but it doesn't work.
>
> For example
>
> (define (test x)
>   (case x
> [(eof) eof]
> [else  "else"]))
>
>
> (test eof) will then evaluate to "else" despite (equal? eof eof) evaluating 
> to #t.
>
> Why ?
>
>
>
> --
> You received this message because you are subscribed to the Google Groups 
> "Racket Users" group.
> To unsubscribe from this group and stop receiving emails from it, send an 
> email to racket-users+unsubscr...@googlegroups.com.
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-- 
Jay McCarthy
Associate Professor
PLT @ CS @ UMass Lowell
http://jeapostrophe.github.io

   "Wherefore, be not weary in well-doing,
  for ye are laying the foundation of a great work.
And out of small things proceedeth that which is great."
  - D 64:33

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[racket-users] Case and eof

[rom cgb]

Hi,

Trying to use eof in a case expression but it doesn't work.

For example

(define (test x)
  (case x
[(eof) eof]
[else  "else"]))


(test eof) will then evaluate to "else" despite (equal? eof eof) evaluating to 
#t. 

Why ?



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