[erlang-questions] if-elseif-else trick

[andrei zavada]

One neat (for some definition of 'neat') trick to do away with `true`
for the semantic `else` is `el/=se` (spotted in riak code).

On Mon, 18 Feb 2019 at 16:36, Raimo Niskanen
<raimo+erlang-questions@REDACTED> wrote:
>
> On Mon, Feb 18, 2019 at 06:34:11PM +0900, zxq9@REDACTED wrote:
> > On 2019年2月18日月曜日 9時02分11秒 JST Andreas Schultz wrote:
> > > Hi Viktor,
> > >
> : :
> > > but why would you use such a thing when you can simply write:
> > >
> > > if X > 0 -> pos;
> > >    X < 0 -> neg;
> > >    true -> zero
> > > end.
> >
> >
> > `if ... true` is a code stink.
>
> That is a personal opinion.
>
> if ... end selects the clause of the first succesful guard expression,
> and 'true' is simply a succesful guard expression.
>
> > Be explicit in your range tests -- that is what `if` is actually good at:
> >
> >   if
> >     X >  0 -> pos;
> >     X <  0 -> neg;
> >     X == 0 -> zero
> >   end
>
> That is a pretty example that is obviois about which cases it handles,
> (note that it also handles non-numbers since all terms have an order)
> but sometimes you instead want it to be obvious that you handle all cases.
>
>     if
>         is_integer(X), 0 =< X -> non_negative;
>         true -> erlang:error(badarg)
>     end
>
> >
> > If you find yourself *needing* a `true` catchall, you should be writing a function head or `case`.
>
> I have no problem using 'if' for that.  The 'true' catchall in 'if' is just
> as much a catchall as the '_' catchall in 'case'.
>
>
> >
> >
> > That said...
> > The original premise of this thread is based on a misunderstanding of `if` and probably inexperience with `case`.
>
> Agreed
>
> >
> >
> > -Craig
>
> --
>
> / Raimo Niskanen, Erlang/OTP, Ericsson AB
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