[erlang-questions] specs for fixed length lists

Tony Rogvall <>
Sun Jul 8 11:48:28 CEST 2012


On 7 jul 2012, at 21:53, Richard Carlsson wrote:

> On 2012-07-07 13:57, Tony Rogvall wrote:
>> Try this:
>> 
>>     -type buttons() :: [boolean() | [boolean() | [boolean() |
>> [boolean() | []]]]].
> 
> You certainly can _write_ it like that, just like you can write "1+1" instead of "2". To a tool like Dialyzer, it will still just be interpreted as a (nonempty) list of boolean(). The exact number of elements is not tracked. And if you for example try to say "[atom() | [integer() | []]]", it will just be the same as saying "nonempty list of atom()|integer()" - the order of occurrence of the element types is also not part of the list type.
> 
But you can not _write_ (why do you use underscore before and after write? ) things like 
-spec get_buttons1() -> {ok, [boolean(),boolean(),boolean(),boolean()]}.
Because you will get a syntax error!. 
Why is the "dotted pair" notation supported if it does not work ?
It can not be harder to support then supporting pairs ? (For the record I do think it could be a bit harder :)

BTW 
	The 1+1 = 2 example was totally silly in my opinion.

/Tony


>    /Richard
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