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Re: Favourite Pattern for Processing Zero, Once, Multiple

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"Shao Miller" <sha0.miller@gmail.com> wrote in message
news:kco8gq$mao$1@dont-email.me...
> On 1/10/2013 22:20, Ben Bacarisse wrote:

>> Does this crop up for real?  I'd try to find a cleaner way to write the
>> whole bar() + foo() interaction.

That's the key I think (see below).

> Thanks, BartC, for your response (I sent you an e-mail, but "no such
> user").

It was a valid email at one time (Try using bcas instead of bc)

> Sometimes 'bar' will have multiple characters to emit, and the caller
> needs to call it multiple times to get all of the characters.  ("Here's
> one translated character, but call me again because I have more.")
>
> Could be useful for escape sequences: "123${special}ABC" where the '$'
> through until the 'l' wouldn't emit anything, but then the subsequent '}'
> would cause some special sequence to be emitted, where 'bar' would know
> what to emit, but would have to be queried repeatedly until it finished
> emitting the special sequence.

At first glance this seems perfectly straightforward: bar is just called
repeatedly until the 'EOF' marker you mention is returned. In this case,
bar() returns the next character in the sequence, rather than some code. If
the "123" in your example was consumed with no output, then bar wouldn't
return until there was something to return, in this case the first character
of whatever replaces "${special}".

But it gets more complicated when you have to consider where this input
string comes from. There might be some global state containing the input
stream, the current position in that stream, and the current position in any
translation string. Or that state might be contained inside bar().

Or perhaps the caller might supply bar() with the next input character (and
bar() needs some look-ahead to operate properly). Or a pointer to a struct
containing the state (so that bar() can be called from different places, all
with their own strings to translate).

> So I thought it was a bit of an interesting challenge and I wonder what
> strategies folks might've or might come up with, as a general pattern.

It's not clear what the roles of bar() and foo() are. Maybe one of those 
returns the next translated character, but some more information is needed. 
The whole thing seems a bit like a tokeniser, or at least has some of the 
same problems to be solved.

-- 
Bartc
 

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Favourite Pattern for Processing Zero, Once, Multiple Shao Miller <sha0.miller@gmail.com> - 2013-01-10 17:53 -0500
  Re: Favourite Pattern for Processing Zero, Once, Multiple "BartC" <bc@freeuk.com> - 2013-01-10 23:26 +0000
    Re: Favourite Pattern for Processing Zero, Once, Multiple Shao Miller <sha0.miller@gmail.com> - 2013-01-10 18:49 -0500
      Re: Favourite Pattern for Processing Zero, Once, Multiple "BartC" <bc@freeuk.com> - 2013-01-11 00:23 +0000
  Re: Favourite Pattern for Processing Zero, Once, Multiple Ben Bacarisse <ben.usenet@bsb.me.uk> - 2013-01-11 03:20 +0000
    Re: Favourite Pattern for Processing Zero, Once, Multiple Shao Miller <sha0.miller@gmail.com> - 2013-01-11 00:38 -0500
      Re: Favourite Pattern for Processing Zero, Once, Multiple Bart van Ingen Schenau <bart@ingen.ddns.info.invalid> - 2013-01-11 12:10 +0000
        Re: Favourite Pattern for Processing Zero, Once, Multiple Shao Miller <sha0.miller@gmail.com> - 2013-01-11 13:37 -0500
      Re: Favourite Pattern for Processing Zero, Once, Multiple "BartC" <bc@freeuk.com> - 2013-01-11 12:15 +0000
        Re: Favourite Pattern for Processing Zero, Once, Multiple Shao Miller <sha0.miller@gmail.com> - 2013-01-11 13:56 -0500
          Re: Favourite Pattern for Processing Zero, Once, Multiple Fred K <fred.l.kleinschmidt@gmail.com> - 2013-01-11 11:15 -0800
            Re: Favourite Pattern for Processing Zero, Once, Multiple Shao Miller <sha0.miller@gmail.com> - 2013-01-11 14:28 -0500
          Re: Favourite Pattern for Processing Zero, Once, Multiple Greg Martin <greg@softsprocket.com> - 2013-01-11 11:22 -0800
            Re: Favourite Pattern for Processing Zero, Once, Multiple Shao Miller <sha0.miller@gmail.com> - 2013-01-11 15:23 -0500
              Re: Favourite Pattern for Processing Zero, Once, Multiple Greg Martin <greg@softsprocket.com> - 2013-01-11 13:09 -0800
          Re: Favourite Pattern for Processing Zero, Once, Multiple "BartC" <bc@freeuk.com> - 2013-01-11 22:09 +0000
          Re: Favourite Pattern for Processing Zero, Once, Multiple Paul N <gw7rib@aol.com> - 2013-01-12 04:49 -0800
            Re: Favourite Pattern for Processing Zero, Once, Multiple Shao Miller <sha0.miller@gmail.com> - 2013-01-13 20:30 -0500
  Re: Favourite Pattern for Processing Zero, Once, Multiple glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2013-01-11 21:02 +0000
  Re: Favourite Pattern for Processing Zero, Once, Multiple Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2013-01-13 20:28 +0200
    Re: Favourite Pattern for Processing Zero, Once, Multiple Shao Miller <sha0.miller@gmail.com> - 2013-01-13 16:12 -0500

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