[erlang-questions] If Condition vs. Multiple Function Clauses
Mahesh Paolini-Subramanya
<>
Sat Jun 15 10:43:00 CEST 2013
Via LYSE and ROK - and with the forlorn hope that this doesn't start up again :-) -->
It may be more FAMILIAR, but that doesn't mean 'else' is a good thing. I know that writing '; true ->' is a very easy way to get 'else' in Erlang, but we have a couple of decades of psychology-of-programming results to show that it's a bad idea. I have started to replace:
by
if X > Y -> a() if X > Y -> a()
; true -> b() ; X =< Y -> b()
end end
if X > Y -> a() if X > Y -> a()
; X < Y -> b() ; X < Y -> b()
; true -> c() ; X ==Y -> c()
end end
which I find mildly annoying when _writing_ the code but enormously helpful when _reading_ it.
Speaking for myself, I've pretty much gotten to the point where I don't notice it.
Heck, I barely notice syntax anymore. About the best analogy I can come up with is spoken languages (adjectives after nouns in Italian? The Horror! The Horror!). It may seem strange at first, but you don't even notice it after a few days…
Cheers
Mahesh Paolini-Subramanya
That Tall Bald Indian Guy...
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On Jun 15, 2013, at 2:40 AM, Steve Davis <> wrote:
> I strongly (personally) dislike use of "if" syntax, but only because of the counterintuitive "true" evaluation.
>
> What if the language were to return the atom "else" instead of "true"?
>
> I doubt that would be considered "better" but it would sure make things more readable...
>
> /s
>
> On Friday, June 14, 2013 8:06:33 AM UTC-5, Lars Herbach wrote:
> Hi List,
> I'm currently working myself through the "Études for Erlang" book [1] and in exercise it wks's to write a recursive function, calculating the greatest common divisor for two numbers N and M. The suggested solution is a single gcd/2 function with an If condition and recursion:
>
> gcd(M, N) ->
> if M == N -> M;
> M > N -> gcd(M - N, N;
> true -> gcd(M, N - M)
> end.
>
> I by myself took another way, working with multiple function clauses (did I name it right?):
>
> gcd(M, N) when M == N ->
> M;
> gcd(M, N) when M > N ->
> gcd(M - N, N);
> gcd(M, N) ->
> gcd(M, N - M).
>
> Now I've got two questions about that:
> 1) Is my solution still recursive, since I practically call different functions?
> 2) Are there any benefits in regards of efficiancy for the first solution?
>
> Thanks,
> Lars.
>
>
> [1]: http://shop.oreilly.com/product/0636920030034.do
> _______________________________________________
> erlang-questions mailing list
>
> http://erlang.org/mailman/listinfo/erlang-questions
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