eof in Common Lisp

[wan...@exploited.barmy.army]

Hi,

From what I read, to detect eof in lisp when using read, one
uses the keyword parameters like eof-error-p and eof-value.
Thing is, I can't get these to work. I'm using CMUCL and
tried Harlequin FreeLisp and I get errors like the following:

(read t :eof-error-p nil) => EOF is treated as an error anyway

(read t :eof-error-p nil :eof-value 'done) => get an error about
too many params.

Would someone be kind enough to provide me with an example
of how to use this feature properly?

Thanks.

--
Ahmed

My email address is invalid. To reply, mail to punkrock at
cs dot uh dot edu.

[Erik Naggum]

* wan...@exploited.barmy.army

| From what I read, to detect eof in lisp when using read, one uses the
| keyword parameters like eof-error-p and eof-value.

^^^^^^^
where did you read that?

| Would someone be kind enough to provide me with an example of how to use
| this feature properly?

try (KERNEL:%FUNCTION-ARGLIST #'READ) in CMUCL, check the HyperSpec or
look more close in whatever textbook you're using.

note that even if EOF-ERROR-P is false, an error is caused if RECURSIVE-P
is true, i.e., the EOF-VALUE argument is returned only if the end of file
occurs at top-level.

if you want to be certain that you do not detect end of file prematurely,
pass a guaranteed unique value as EOF-VALUE, such as a fresh, uninterned
symbol, a fresh cons cell, or somesuch.

#:Erik
--
God grant me serenity to accept the code I cannot change,
courage to change the code I can, and wisdom to know the difference.

[Rainer Joswig]

In article <6dsg64$mg8$1...@Masala.CC.UH.EDU>, wan...@exploited.barmy.army wrote:

> Hi,

>
> From what I read, to detect eof in lisp when using read, one
> uses the keyword parameters like eof-error-p and eof-value.

> Thing is, I can't get these to work. I'm using CMUCL and
> tried Harlequin FreeLisp and I get errors like the following:
>
> (read t :eof-error-p nil) => EOF is treated as an error anyway
>
> (read t :eof-error-p nil :eof-value 'done) => get an error about
> too many params.
>

These are not keyword parameters - but optional parameters.

READ &optional input-stream eof-error-p eof-value recursivep
[Function]
reads the printed representation of a single object from input-stream,
builds a corresponding object, and returns the object.

Use:

(read t nil 'done)

--
http://www.lavielle.com/~joswig/

[wan...@exploited.barmy.army]

Thanks for the assistance, and sorry for my silly blunder.

I saw references to parameter names in CLTL2 and I just assumed
that the parameters were being explicitly mentioned for a reason,
and one logical blunder led to another and the next thing I knew
I was trying to use them as keywords.

I apologize for wasting bandwidth, when I should have been
paying more attention to the document.

Thank you,
Ahmed

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