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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Why is your second alternative (viz., “f(X) -> Y | exit(..)”) not the default preferred option for all Erlang code?  It seems to express your meaning and intent better than a tuple return code.  You can always wrap it in a try if you want to catch the error.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Me, I always have trouble deciding between exit(…) and error(…).<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Cheers,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>DBM<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><div style='border:none;border-left:solid blue 1.5pt;padding:0in 0in 0in 4.0pt'><div><div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> erlang-questions-bounces@erlang.org [mailto:erlang-questions-bounces@erlang.org] <b>On Behalf Of </b>Joe Armstrong<br><b>Sent:</b> Monday, November 14, 2011 5:25 AM<br><b>To:</b> Steve Davis<br><b>Cc:</b> erlang-questions@erlang.org<br><b>Subject:</b> Re: [erlang-questions] When to return {ok, Value} or just the Value<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal style='margin-bottom:12.0pt'>You have several alternatives<br><br>      f(X) -> Y                  uses if you know computing f(X) always returns Y for all X<br><br>      f(X) -> Y | exit(..)     if "most" values of f(X) are valid and you could not take care of the<br>                                     error case in the caller<br><br>      f(X) -> {ok, Y} | {error, Z}   if some values of X cause f(X) to fail and you want to take care<br>                                                of the error in the caller.<br><br>      returning {ok, Y} | {error,Z} is a strong signal to the person reading the code that the caller will<br>      do something with *both* return values.<br><br>      The caller might just write {ok,Val} = f(X) and not handle the error case, but the reader of the<br>code will think - "ahh something might go wrong, and this code may need to be fixed later."<br>it's not just what you write but what will be inferred by the reader.<br><br>      Code using {ok, Val} | {error, Why} tends to lead to messy cascades of nested cases, so the<br>      Y | exit(...) code style looks prettier.<br><br>      The entire picture gets complicated sing catch/throw/try etc. so there is no "right" answer.<br><br>      I guess you should choose be locally consistent in your code - choose a convention and stick to it<br>in your code and chose the variant that will be easiest to read and maintain. If you end up with<br>loads of nested cases/trys you might have chosen the wrong convention.<br><br>Cheers<br><br>/Joe<br>                                          <br><br><br><o:p></o:p></p><div><p class=MsoNormal>On Sun, Nov 13, 2011 at 1:35 AM, Steve Davis <<a href="mailto:steven.charles.davis@gmail.com">steven.charles.davis@gmail.com</a>> wrote:<o:p></o:p></p><p class=MsoNormal>Is there a rule-of-thumb guidance as to when it is the right "time" to<br>return {ok, Value} and when to return just the raw value.<br><br>Both are valid approaches according to the coding guidelines. The<br>libraries do both.<br><br>All and any comments/observations appreciated.<br><br>best,<br>/s<br>_______________________________________________<br>erlang-questions mailing list<br><a href="mailto:erlang-questions@erlang.org">erlang-questions@erlang.org</a><br><a href="http://erlang.org/mailman/listinfo/erlang-questions" target="_blank">http://erlang.org/mailman/listinfo/erlang-questions</a><o:p></o:p></p></div><p class=MsoNormal><o:p> </o:p></p></div></div></body></html>