Path: utzoo!attcan!uunet!samsung!zaphod.mps.ohio-state.edu!usc!bbn!jr@bbn.com
From: jr@bbn.com (John Robinson)
Newsgroups: comp.emacs
Subject: Re: Need read-number function
Message-ID: <51906@bbn.COM>
Date: 8 Feb 90 15:41:55 GMT
References: <4300068@m.cs.uiuc.edu> <13690@phoenix.Princeton.EDU>
Sender: news@bbn.COM
Reply-To: jr@bbn.com (John Robinson)
Organization: BBN Systems and Technologies Corporation, Cambridge MA
Lines: 41
In-reply-to: eliot@phoenix.Princeton.EDU (Eliot Handelman)

In article <4300068@m.cs.uiuc.edu>, reingold@m.cs writes:
>
>I need a function read-number that would behave like (interactive "n");
>that is, it would keep trying until a numeric value was typed.

In article <1990Feb8.132524.1694@talos.uu.net>, kjones@talos (Kyle Jones) writes:
>Yah, I had to code this one myself.  I don't know if a function like
>this should be standard in the distribution or not.  Common Lisp's
>elephantiasis is largely due to adopting functions from everyone's
>toolbox.

[defun omited].  It occurred to me that you could generalize Kyle's
function into somthing like:

  (read-thing prompt checker-function &optional initial-contents)

which asks for a lisp object until it gets one with the right type, as
passed by the checker-function.  Maybe ought to be a macro, or should
accept symbols like 'integer, 'string instead of a function name and
dispatch on them.

In article <13690@phoenix.Princeton.EDU>, eliot@phoenix (Eliot Handelman) writes:
>How's about this:
>
>(defun read-number (number)
>   (interactive "nNumber: ")
>   number)

Yeah, my initial reaction too.  This requires the additional
observation that, to call it from inside lisp code, you need to say:

  (call-interactively 'read-number)

... and there is no easy way to pass it a prompt at run time.  For
that, you would probably want to replace the defined function in the
call-interactively with a lambda-expression, but I'm not sure it is
possible to get the (interactive) part right if you do.  Or (ugh)
evaluate the defun inside the caller...
--
/jr, nee John Robinson     Life did not take over the globe by combat,
jr@bbn.com or bbn!jr          but by networking -- Lynn Margulis