Re: Mechanism to generate annotated "error codes"

From	Don Y <this@isnotme.com>
Newsgroups	comp.lang.c
Subject	Re: Mechanism to generate annotated "error codes"
Date	2012-03-03 12:04 -0700
Organization	Aioe.org NNTP Server
Message-ID	<jitq0d$2fq$1@speranza.aioe.org> (permalink)
References	<jiojq3$3cm$1@speranza.aioe.org> <ea871b51-f766-4da3-ab1a-169434004f0d@p7g2000yqk.googlegroups.com> <jisie1$1qf$1@speranza.aioe.org> <c58608b7-d3cf-4b1b-afb6-30f5fab77bcc@gr6g2000vbb.googlegroups.com>

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Hi Malcolm,

On 3/3/2012 4:32 AM, Malcolm McLean wrote:
> On Mar 3, 7:49 am, Don Y<t...@isnotme.com>  wrote:
>> On 3/2/2012 11:13 PM, Malcolm McLean wrote:

>>> The first thing to do is to divide your code into "pure functions" and
>>> "procedures". A pure function shuffles bits, a prodeucre shuffles bits
>>> and does IO.
>>
>> So, your classification treats a parser as a "pure function" -- if
>> the I/O has been handled outside of the scope of the parser.
>
> A parser is a pure function (assuming IO is not handled by the
> function). It takes one sequence of bits - the script - and it returns
> a another sequence of bits - the result. So all it's doing is
> shuffling bits about in memory. If a pure function calls a procedure,
> it's no longer a pure function.

Understood.

> However most parsers will do IO. That leads to a question. If a pure
> function takes a function pointer as a parameter, and that parameter
> is to a procedure, is it still a pure function? The answer is no, but
> here the classification is beginning to lose its usefulness.
>
> Parsers are an obvious case of invalid input not being reasonably
> caught by caller. You could require that caller pass only correct
> scripts to the parser, but that means caller has to do almost as much
> work as the parser itself to verify that the script is correct. So you

That was the point I was trying to bring out.  Do you call the
"parameter" passed to it a "programming error"?  That would imply
the caller had the responsibility of checking it for correctness
(eliminating the need for the parser's functionality).

> have to treat malformed scripts as part of the normal flow control of
> the parser. The caler's then got the problem. If the script was typed
> into the source byt he programer, it's an internal error. If the
> script was provided by outside, it should usually be treated as normal
> flow control - you expect complex user-provided scripts to be
> malformed.

I think "expect" is overly cynical.  I would say "you PREPARE FOR
<any input> to be 'malformed'" -- since you can't control the
outside world.

Returning to my original example (scanning a string of chars to
extract the numeric value expected to be represented therein),
that function (pure function using your terminology) can report
the nature of any "incompatible input" to any degree of detail
that it considers appropriate.  Not just "hey, I couldn't find
a valid 'number' in this mess..."

Those reports make sense in the context of a function that
is responsible for extracting the numeric value represented by a
string of characters.  REGARDLESS OF WHAT THAT NUMBER IS BEING
USED FOR.  And, regardless of the actual value!

E.g., if that routine also had the responsibility of testing that
the value was within a particular set of bounds, it could add
"Value specified exceeds the maximum allowed.", etc. to its
lexicon of errors.

None of these reports need to know whether the "value" is being
used as a representation of AGE, azimuth/elevation, speed,
stock market index, etc.  You are dealing with a *value* -- just
like when you complain that the first letter of a sentence is
not capitalized (you don't even look at the CONTENT of the
sentence to understand the nature of that "report").

But, you obviously don't want that "pure function" to become
a "procedure" by virtue of informing the user directly of
this error (this would also badly contort the design of
your code).

Nor do you need to return the text of the message to the caller!
(how do you decide whether you should return the en_US version
of the message or the es version?)

Instead, return an identifier that allows the caller to fetch
a version of the error that *it* considers appropriate.

It, in turn, can embellish -- or replace -- that message with
something appropriate to its understanding of the application.
E.g., perhaps the caller is responsible for obtaining the
coordinates of a point in 2D space.  It *uses* the called routine
to parse the string (that is provided to *it* by ITS caller!)
for the X coordinate, then the Y coordinate.  An error reported
during the first parse might cause it to report an error to
*it's* caller like:  "Bad value for X coordinate." AUGMENTED
by the report returned by the function that had actually
detected the lower level error "Non-numeric character encountered
in value."

Or not (depends on the range of errors that you document
get_point() as reporting).  You could, instead, ignore the
detail presented to you by any of your "underlings" and
just report:  "Bad point".

Thread

Mechanism to generate annotated "error codes" Don Y <this@isnotme.com> - 2012-03-01 12:48 -0700
  Re: Mechanism to generate annotated "error codes" Willem <willem@toad.stack.nl> - 2012-03-01 21:29 +0000
    Re: Mechanism to generate annotated "error codes" Don Y <this@isnotme.com> - 2012-03-01 16:53 -0700
  Re: Mechanism to generate annotated "error codes" William Ahern <william@wilbur.25thandClement.com> - 2012-03-01 14:13 -0800
    Re: Mechanism to generate annotated "error codes" Don Y <this@isnotme.com> - 2012-03-01 22:07 -0700
  Re: Mechanism to generate annotated "error codes" Shao Miller <sha0.miller@gmail.com> - 2012-03-01 17:53 -0500
    Re: Mechanism to generate annotated "error codes" Don Y <this@isnotme.com> - 2012-03-01 23:05 -0700
      Re: Mechanism to generate annotated "error codes" Shao Miller <sha0.miller@gmail.com> - 2012-03-02 01:50 -0500
        Re: Mechanism to generate annotated "error codes" Don Y <this@isnotme.com> - 2012-03-02 00:43 -0700
          Re: Mechanism to generate annotated "error codes" Shao Miller <sha0.miller@gmail.com> - 2012-03-03 17:58 -0500
            Re: Mechanism to generate annotated "error codes" Shao Miller <sha0.miller@gmail.com> - 2012-03-04 03:16 -0500
              Re: Mechanism to generate annotated "error codes" Don Y <this@isnotme.com> - 2012-03-04 13:47 -0700
            Re: Mechanism to generate annotated "error codes" Don Y <this@isnotme.com> - 2012-03-04 13:45 -0700
              Re: Mechanism to generate annotated "error codes" Shao Miller <sha0.miller@gmail.com> - 2012-03-04 18:37 -0500
                Re: Mechanism to generate annotated "error codes" Don Y <this@isnotme.com> - 2012-03-04 22:12 -0700
                Re: Mechanism to generate annotated "error codes" Shao Miller <sha0.miller@gmail.com> - 2012-03-08 01:41 -0500
                Re: Mechanism to generate annotated "error codes" Don Y <this@isnotme.com> - 2012-03-09 14:34 -0700
  Re: Mechanism to generate annotated "error codes" Don Y <this@isnotme.com> - 2012-03-02 00:30 -0700
    Re: Mechanism to generate annotated "error codes" Keith Thompson <kst-u@mib.org> - 2012-03-02 02:05 -0800
      Re: Mechanism to generate annotated "error codes" Kaz Kylheku <kaz@kylheku.com> - 2012-03-02 10:47 +0000
      Re: Mechanism to generate annotated "error codes" gazelle@shell.xmission.com (Kenny McCormack) - 2012-03-02 14:18 +0000
      Re: Mechanism to generate annotated "error codes" Don Y <this@isnotme.com> - 2012-03-02 10:46 -0700
        Re: Mechanism to generate annotated "error codes" James Kuyper <jameskuyper@verizon.net> - 2012-03-02 14:08 -0500
          Re: Mechanism to generate annotated "error codes" Don Y <this@isnotme.com> - 2012-03-02 12:38 -0700
        Re: Mechanism to generate annotated "error codes" Kaz Kylheku <kaz@kylheku.com> - 2012-03-02 22:57 +0000
          Re: Mechanism to generate annotated "error codes" Don Y <this@isnotme.com> - 2012-03-02 17:14 -0700
            Re: Mechanism to generate annotated "error codes" Kaz Kylheku <kaz@kylheku.com> - 2012-03-03 02:25 +0000
            Re: Mechanism to generate annotated "error codes" James Kuyper <jameskuyper@verizon.net> - 2012-03-03 06:10 -0500
              Re: Mechanism to generate annotated "error codes" Shao Miller <sha0.miller@gmail.com> - 2012-03-03 16:12 -0500
        Re: Mechanism to generate annotated "error codes" Keith Thompson <kst-u@mib.org> - 2012-03-03 04:04 -0800
          Re: Mechanism to generate annotated "error codes" Kaz Kylheku <kaz@kylheku.com> - 2012-03-03 15:05 +0000
            Re: Mechanism to generate annotated "error codes" Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-03-03 16:25 +0000
          Re: Mechanism to generate annotated "error codes" Shao Miller <sha0.miller@gmail.com> - 2012-03-03 16:26 -0500
            Re: Mechanism to generate annotated "error codes" Keith Thompson <kst-u@mib.org> - 2012-03-03 13:40 -0800
      Re: Mechanism to generate annotated "error codes" Ian Collins <ian-news@hotmail.com> - 2012-03-03 12:03 +1300
        Re: Mechanism to generate annotated "error codes" Keith Thompson <kst-u@mib.org> - 2012-03-02 15:45 -0800
        Re: Mechanism to generate annotated "error codes" Don Y <this@isnotme.com> - 2012-03-02 17:18 -0700
      Re: Mechanism to generate annotated "error codes" blp@cs.stanford.edu (Ben Pfaff) - 2012-03-02 15:08 -0800
      Re: Mechanism to generate annotated "error codes" "BartC" <bc@freeuk.com> - 2012-03-03 10:30 +0000
        Re: Mechanism to generate annotated "error codes" James Kuyper <jameskuyper@verizon.net> - 2012-03-03 06:19 -0500
        Re: Mechanism to generate annotated "error codes" Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-03-03 15:15 +0200
        Re: Mechanism to generate annotated "error codes" Kaz Kylheku <kaz@kylheku.com> - 2012-03-03 14:52 +0000
          Re: Mechanism to generate annotated "error codes" Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-03-03 07:39 -0800
            Re: Mechanism to generate annotated "error codes" Jonathan Leffler <jleffler@earthlink.net> - 2012-03-03 23:56 -0800
              Re: Mechanism to generate annotated "error codes" Ian Collins <ian-news@hotmail.com> - 2012-03-05 09:20 +1300
                Re: Mechanism to generate annotated "error codes" Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-03-04 13:28 -0800
                Re: Mechanism to generate annotated "error codes" Ian Collins <ian-news@hotmail.com> - 2012-03-05 10:56 +1300
          Re: Mechanism to generate annotated "error codes" "BartC" <bc@freeuk.com> - 2012-03-03 17:02 +0000
        Re: Mechanism to generate annotated "error codes" Keith Thompson <kst-u@mib.org> - 2012-03-03 12:30 -0800
    Re: Mechanism to generate annotated "error codes" Don Y <this@isnotme.com> - 2012-03-03 19:15 -0700
      Re: Mechanism to generate annotated "error codes" Kaz Kylheku <kaz@kylheku.com> - 2012-03-04 03:20 +0000
        Re: Mechanism to generate annotated "error codes" Don Y <this@isnotme.com> - 2012-03-04 11:03 -0700
      Re: Mechanism to generate annotated "error codes" Don Y <this@isnotme.com> - 2012-03-04 16:31 -0700
        Re: Mechanism to generate annotated "error codes" Don Y <this@isnotme.com> - 2012-03-04 23:04 -0700
  Re: Mechanism to generate annotated "error codes" Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-03-02 22:13 -0800
    Re: Mechanism to generate annotated "error codes" Don Y <this@isnotme.com> - 2012-03-03 00:49 -0700
      Re: Mechanism to generate annotated "error codes" Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-03-03 03:32 -0800
        Re: Mechanism to generate annotated "error codes" Don Y <this@isnotme.com> - 2012-03-03 12:04 -0700
          Re: Mechanism to generate annotated "error codes" Lowell Gilbert <lgusenet@be-well.ilk.org> - 2012-03-03 15:06 -0500
            Re: Mechanism to generate annotated "error codes" Don Y <this@isnotme.com> - 2012-03-03 14:38 -0700
          Re: Mechanism to generate annotated "error codes" Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-03-03 12:15 -0800
            Re: Mechanism to generate annotated "error codes" Don Y <this@isnotme.com> - 2012-03-03 16:51 -0700
              Re: Mechanism to generate annotated "error codes" Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-03-04 14:08 -0800
                Re: Mechanism to generate annotated "error codes" Don Y <this@isnotme.com> - 2012-03-04 15:56 -0700
      Re: Mechanism to generate annotated "error codes" Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-03-03 03:45 -0800
        Re: Mechanism to generate annotated "error codes" Lowell Gilbert <lgusenet@be-well.ilk.org> - 2012-03-03 14:11 -0500
          Re: Mechanism to generate annotated "error codes" Don Y <this@isnotme.com> - 2012-03-03 13:03 -0700
        Re: Mechanism to generate annotated "error codes" Don Y <this@isnotme.com> - 2012-03-03 12:32 -0700
      Re: Mechanism to generate annotated "error codes" Don Y <this@isnotme.com> - 2012-03-03 15:04 -0700
        Re: Mechanism to generate annotated "error codes" Ian Collins <ian-news@hotmail.com> - 2012-03-04 11:09 +1300
          Re: Mechanism to generate annotated "error codes" Don Y <this@isnotme.com> - 2012-03-03 16:55 -0700
            Re: Mechanism to generate annotated "error codes" Ian Collins <ian-news@hotmail.com> - 2012-03-04 13:04 +1300
              Re: Mechanism to generate annotated "error codes" Don Y <this@isnotme.com> - 2012-03-03 18:24 -0700
        Re: Mechanism to generate annotated "error codes" Malcolm McLean <malcolm.mclean5@btinternet.com> - 2012-03-03 14:30 -0800
          Re: Mechanism to generate annotated "error codes" Don Y <this@isnotme.com> - 2012-03-03 17:06 -0700
  Re: Mechanism to generate annotated "error codes" Ian Collins <ian-news@hotmail.com> - 2012-03-05 10:09 +1300
    Re: Mechanism to generate annotated "error codes" Don Y <this@isnotme.com> - 2012-03-04 16:03 -0700
      Re: Mechanism to generate annotated "error codes" Ian Collins <ian-news@hotmail.com> - 2012-03-05 13:26 +1300
        Re: Mechanism to generate annotated "error codes" Don Y <this@isnotme.com> - 2012-03-04 22:21 -0700
          Re: Mechanism to generate annotated "error codes" Ian Collins <ian-news@hotmail.com> - 2012-03-05 20:46 +1300
            Re: Mechanism to generate annotated "error codes" Don Y <this@isnotme.com> - 2012-03-05 10:54 -0700
              Re: Mechanism to generate annotated "error codes" Ian Collins <ian-news@hotmail.com> - 2012-03-06 10:02 +1300
                Re: Mechanism to generate annotated "error codes" Don Y <this@isnotme.com> - 2012-03-05 16:09 -0700
            Re: Mechanism to generate annotated "error codes" "BartC" <bc@freeuk.com> - 2012-03-06 10:54 +0000
              Re: Mechanism to generate annotated "error codes" Ian Collins <ian-news@hotmail.com> - 2012-03-07 07:22 +1300
  Re: Mechanism to generate annotated "error codes" gordonb.8sa24@burditt.org (Gordon Burditt) - 2012-03-06 08:51 -0600
    Re: Mechanism to generate annotated "error codes" Don Y <this@isnotme.com> - 2012-03-06 11:21 -0700

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