[erlang-questions] Idiom for multiple case matches

Kevin Scaldeferri <>
Mon Nov 10 19:44:52 CET 2008


On Nov 9, 2008, at 3:06 PM, mats cronqvist wrote:

> Michael Radford <> writes:
>
>> I hesitate to wade into this cranky-fest, but IMO this is extremely
>> clear and easy to read:
>>
>> 	is_vowel ($a) -> true;
>> 	is_vowel ($e) -> true;
>> 	is_vowel ($i) -> true;
>> 	is_vowel ($o) -> true;
>> 	is_vowel ($u) -> true;
>> 	is_vowel (_) -> false.
>>
>> That's just saying directly what you mean in a language that's nice
>> enough to make it reasonably efficient.
>
>  and what you mean is presumably that 'is_vowel' is a function that
>  returns 'true' if its argument is a member of the list "aeiou",
>  otherwise 'false'.
>
>  the fact that this is a fairly common task is of course the reason
>  why lists:member/2 exists in the first place. so by not using
>  lists:member/2 here, you are obfuscating the fact that you are
>  indeed testing if something is a member of a list.

Well, if you want to be pedantic, that's completely wrong.  There's  
nothing list-like about the collection of vowels.  It's a set.  So,  
clearly, in the interest of clarity, we should use set:member/2, even  
though that's orders of magnitude slower.


>  and the style of cut-and-paste programming you use is also bad. for
>  example, it's easy to get lost in the paste-fest and forget that "y"
>  is a vowel.

I've been watching this discussion waiting for someone to point out  
the glaring problem with this whole exercise, which is that "vowel- 
ness" is language-dependent.  So, in that sense, all approaches which  
have been presented so far are wrong.


-kevin




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