[erlang-bugs] Document of lists:append/2
Bengt Kleberg
bengt.kleberg@REDACTED
Mon Feb 10 07:45:40 CET 2014
Greetings,
Some functions have arguments that would be time consuming to check for
correctness. This might be a reason for not mandating a check of all
arguments.
bengt
On Mon, 2014-02-10 at 01:37 -0500, Heinz Nikolaus Gies wrote:
> I somewhat disagree on that point. Shouldn’t functions crash given
> badly typed inputs? That sounds like the reasonable thing to to when
> following the fail early paradigm and I always got the impression a
> lot of the functions in the core libraries happily die a tragic death
> if a wrong input comes too close to them.
> ---
> Cheers,
> Heinz Nikolaus Gies
> heinz@REDACTED
>
>
>
>
>
> On Feb 9, 2014, at 11:43 PM, Bob Ippolito <bob@REDACTED> wrote:
>
> > If you assume that all functions have undefined behavior when given
> > incorrectly typed inputs, it's perfectly consistent. Erlang code
> > tends to assume correctly typed input because it's simpler to
> > implement and the types can often be checked mechanically with tools
> > such as dialyzer.
> >
> > On Sunday, February 9, 2014, Yoshihiro Tanaka <hirotnkg@REDACTED>
> > wrote:
> > Right. I guess I'm questioning the accuracy of the document.
> >
> >
> > On Sun, Feb 9, 2014 at 7:52 PM, Siraaj Khandkar
> > <siraaj@REDACTED> wrote:
> > This is just a surprising side effect of dynamic
> > typing. To perform the
> > append, the left list is traversed and the right is
> > just blindly used as
> > a tail, so it is never introspected and thus never
> > has an opportunity to
> > crash.
> >
> >
> > On 2/9/14, 10:30 PM, Yoshihiro Tanaka wrote:
> > > Hi,
> > >
> > > In the
> > document :http://www.erlang.org/doc/man/lists.html#append-2
> > > It says:
> > > append(List1, List2) -> List3, List1 = List2 =
> > List3 = [T], T = term.
> > >
> > > But considering the following behavior, it does
> > not look correct:
> > >
> > > 1> [] ++ undef.
> > > undef
> > > 2> undef ++ [].
> > > ** exception error: bad argument
> > > in operator ++/2
> > > called as undef ++ []
> > > 3> [a,b] ++ undef.
> > > [a,b|undef]
> > > 4>
> > >
> > >
> > > Thoughts ?
> > >
> > >
> > > Thank you
> > > Yoshihiro
> >
> >
> >
> > _______________________________________________
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> > erlang-bugs@REDACTED
> > http://erlang.org/mailman/listinfo/erlang-bugs
>
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