[erlang-questions] Maps branch and disclaimers

Chris King <>
Tue Oct 29 20:51:17 CET 2013


On Tue, Oct 29, 2013 at 3:41 PM, Jesper Louis Andersen <
> wrote:

>
> view(eq) -> 0;
> view(lt) -> -1;
> view(gt) -> 1.
>
> This function is exhaustive in the input type.
>

No it's not.  Unless you define the input type as :- type order() :: eq |
lt | gt.  Well, you can do the same thing with integers in Erlang: :- type
order() :: -1 | 0 | 1.


> Another problem with an integer is that
>
> compare(X, Y) * compare(Y, Z) is a valid expression, but it has no meaning
> whatsoever.
>

And with atoms, list_to_atom(lists:append(atom_to_list(X), atom_to_list(Y))
is equally meaningless.
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