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Re: Forth on spoj.com

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Julian Fondren <julian.fondren@gmail.com> writes:
>The challenges also seemed tricky in a bad way: the
>first challenge has you write a program that "stops processing input"
>when it reads in 42 on a line, this somehow meaning that it must still
>exhaust its input source after reading that number, which is a
>ludicrous thing to do.

It actually turns out that this helps make the solution shorter, see
below.

I took quite a while (and resorting to Google) to find that problem
(It seems they have ~20000 problems), it's

http://www.spoj.com/problems/TEST/

>  [undefined] stdin [if] 0 constant stdin [then]

If the system does not have STDIN, isn't it better if the program
fails complaining about that rather than failing later at the
READ-FILE?  If a system treats 0 as STDIN, one could test for that
system rather than for the absence of STDIN.

>  1024 8 * constant /buffer
>  create buffer /buffer allot
>  
>  : ?end ( f x -- f x )  over 0= if bye then ;
>  
>  : flush-line ( -- )
>    begin buffer /buffer stdin read-line throw ?end nip if exit then again ;
>  
>  : ?42 ( n -- )
>    buffer over s" 42" compare if buffer swap type cr exit then
>    drop begin flush-line again ;
>  
>  : go ( -- )
>    begin
>      buffer /buffer stdin read-line ?end throw
>      if ?42 else drop flush-line then
>    again ;
>  
>  go

Gforth-specific (but your program already is, because of STDIN):

stdin slurp-fid 2dup s" 42" search and nip - type bye

[not tested on spoj.com, I would have to make an account there]

Note that the AND NIP - sequence produces the right result in case
there is no 42 in the input; if I did not care about that case, I
would have written

stdin slurp-fid 2dup s" 42" search 2drop nip over - type bye

which is conceptually a little simpler, although the code is longer.

If the requirement was not to read past the 42, we could not use
SLURP-FID, but would have to use READ-LINE in a loop, resulting in a
longer program.

- anton
-- 
M. Anton Ertl  http://www.complang.tuwien.ac.at/anton/home.html
comp.lang.forth FAQs: http://www.complang.tuwien.ac.at/forth/faq/toc.html
     New standard: http://www.forth200x.org/forth200x.html
   EuroForth 2016: http://www.euroforth.org/ef16/

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Forth on spoj.com Julian Fondren <julian.fondren@gmail.com> - 2017-02-17 21:29 -0800
  Re: Forth on spoj.com anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-02-18 07:06 +0000
    Re: Forth on spoj.com Julian Fondren <julian.fondren@gmail.com> - 2017-02-18 05:42 -0800
      Re: Forth on spoj.com anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-02-18 14:56 +0000
        Re: Forth on spoj.com Julian Fondren <julian.fondren@gmail.com> - 2017-02-18 12:58 -0800
          Re: Forth on spoj.com albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2017-02-19 11:35 +0100
    Re: Forth on spoj.com albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2017-04-04 14:58 +0200
      Re: Forth on spoj.com Mark Wills <markwills1970@gmail.com> - 2017-04-04 07:40 -0700
        Re: Forth on spoj.com Julian Fondren <julian.fondren@gmail.com> - 2017-04-04 07:52 -0700
          Re: Forth on spoj.com albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2017-04-04 17:36 +0200
          Re: Forth on spoj.com Mark Wills <markwills1970@gmail.com> - 2017-04-04 09:05 -0700
            Re: Forth on spoj.com NN <november.nihal@gmail.com> - 2017-04-04 11:22 -0700
            Re: Forth on spoj.com Julian Fondren <julian.fondren@gmail.com> - 2017-04-04 11:33 -0700
              Re: Forth on spoj.com albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2017-04-05 02:12 +0200
          Re: Forth on spoj.com rickman <gnuarm@gmail.com> - 2017-04-04 16:12 -0400
  Re: Forth on spoj.com Julian Fondren <julian.fondren@gmail.com> - 2017-02-19 22:59 -0800
  Re: Forth on spoj.com Lars Brinkhoff <lars.spam@nocrew.org> - 2017-04-03 20:06 +0200

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