This line will indeed never match :-) Well spotted
Sean
On 12 Mar 2008, at 17:48, David Mercer wrote:
> Perhaps I am misunderstanding the comma or == operator, but for what
> values
> of X will the following guard evaluate to true?
>
> when X == '123', X == '456'
>
> Please advise. Thank-you.
>
> DBM
>
> -----Original Message-----
> From: erlang-questions-bounces@REDACTED
> [mailto:erlang-questions-bounces@REDACTED] On Behalf Of Sean Hinde
> Sent: Tuesday, March 11, 2008 15:06
> To: Mats Cronqvist
> Cc: Erlang mailing list
> Subject: Re: [erlang-questions] erlang sucks
>
>
> On 11 Mar 2008, at 19:26, Mats Cronqvist wrote:
>
>> Sean Hinde wrote:
>>>
>>> On 11 Mar 2008, at 12:47, Mats Cronqvist wrote:
>>>
>>>>
>>>> * 'if' is completely worthless, and should ideally be obsoleted.
>>>
>>> No, no no! I like 'if' It allows some neat constructs that are
>>> horrible with case.
>>
>> i was afraid no one was going to bite... still, I'd like an example
>> or 2.
>
> I'm thinking of things like:
>
> case X of
> _ when X == abc; X == xyz ->
> do_abc_or_xyz();
> _ when X == '123', X == '456' ->
> do_123456()
> '123' ->
> do_123_only();
> fred ->
> do_fred()
> end
>
> vs
>
> if
> X == abc;
> X == xyz ->
> do_abc_or_xyz();
> X == '123',
> X == '456' ->
> do_123456();
> X == '123' ->
> do_123_only();
> X == fred ->
> do_fred()
> end
>
> I don't much like the _ when business.
>
> 'if' is also useful when you want to branch on a bunch of unrelated
> boolean variables in various combinations:
>
> case {X,Y,Z} of
> {true, false, _} ->
> do_a();
> {false, _, true} ->
> do_b();
> _ ->
> do_c()
> end
>
> vs
>
> if
> X and not Y ->
> do_a;
> not X and Z ->
> do_b;
> true ->
> do_c
> end.
>
> I find the second more clearly states the intent. You also don't have
> to remember the positions in the tuple to parse the code (though you
> do need to know that 'not' is stickier* than 'and')
>
> Sean
>
> * IANACS
>
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