[erlang-questions] erlang-questions Digest, Vol 24, Issue 11
Mon May 4 17:25:16 CEST 2009
John Haugeland <> writes:
> > In the "programming rules"
> > http://www.erlang.se/doc/programming_rules.shtml#REF32551
> > ---snip--------------------------------------
> > Use tagged return values.
> My $0.02 is that this advice is, and always has been, hogwash. It is
> a rare function that can return several valid answers. So, the
> default should be to return a valid answer, i.e. one that can be
> used directly, or throw an error.
> My theory is that the people who wrote this "programming rule" were
> (good) C programmers, and thus felt a need to check if the value
> returned was ok before they dared use it.
> Your theory is incorrect. The reason keysearch returns tagged result values
> is that the thing you're searching for might have a value of false.
My theory is likely incorrect, but the only thing keysearch can
find is tuples.
> Tagged results are the only way to return a value such that any value
> is legal; otherwise you need a placeholder value for "nothing found",
> which is not a tolerable admission in basic datastructure behavior.
> There is no way to guarantee that every legal value in a datastructure
> can be unambiguously fetched without tagging.
Perhaps you missed the bit where I said "or throw an error"? 18 lines
or so up? But thanks anyways for the interesting lesson on basic
> Manual advice is correct. It's generally a bad idea to call the
> advice in the manual hogwash when you're still guessing about the
> reason it was there.
Well, I did say it was my $0.02, i.e. I was expressing an opinion.
> This is honestly pretty 101.
And thanks for your refreshing honesty! Alas, I am unfamiliar with
this "101", although I hear she's pretty.
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