Re: Mechanism to generate annotated "error codes"

From	Lowell Gilbert <lgusenet@be-well.ilk.org>
Newsgroups	comp.lang.c
Subject	Re: Mechanism to generate annotated "error codes"
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> <jitq0d$2fq$1@speranza.aioe.org>
Date	2012-03-03 15:06 -0500
Message-ID	<44obsd8n5d.fsf@lowell-desk.lan> (permalink)

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Don Y <this@isnotme.com> writes:

> 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".

The distinction you're making here is about providing appropriate
abstraction. Your technique of ginning up an error value from the file
name and line number doesn't help with this, because the agreement on
symantic returns is between caller and callee -- going further back the
call chain isn't helpful (in fact, it's actively harmful) to maintaining
usable abstrations.

Now that you're thinking in terms of abstractions, it also becomes less
important to worry about exactly what the "identifier" is, and you can
just focus on what it means. It's not a number, it's an object, which
represents everything the caller needs to know about the error. It can
attach additional information, or translate into a different convention
for representing errors, before it reports back to *its* caller.

You'd like a system for adding more information about the error, so each
level can use the specificity of the lower level, and add on the
abstraction that it was hiding from the higher level. This is a
fundamentally different (and vastly more interesting) topic than what
the bottom-level caller reports to its immediate caller.

Be well.
-- 
Lowell Gilbert, embedded/networking software engineer
	 http://be-well.ilk.org/~lowell/

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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