[erlang-questions] Maps branch and disclaimers
Wed Oct 30 17:07:55 CET 2013
On Wed, 30 Oct 2013 11:36:12 -0400, Anthony Ramine <>
> In the foo/1 spec, the binary() doesn’t mean that foo/1 handles *all*
> binaries, it means that if you give something that is not a binary(),
> the call is guaranteed to fail.
Mm, the Erlang reference manual is unclear about the correct
interpretation. Dialyzer's interpretation differs with the -Wunderspecs
$ cat > foo.erl
-spec bar(integer()) -> ok.
bar(42) -> ok.
$ dialyzer foo.erl
done (passed successfully)
$ dialyzer -Wunderspecs foo.erl
foo.erl:3: Type specification foo:bar(integer()) -> 'ok' is a supertype of
the success typing: foo:bar(42) -> 'ok'
done (warnings were emitted)
The latter is more useful to me – I would like to know from the spec that
a function can handle certain inputs (or, in the case of a heterogeneous
map, will produce certain outputs). Knowing that "the function will
return this type or crash" is less useful.
(And the benefit from this interpretation – knowing that given certain
inputs, the function will *definitely* crash, is not generally useful (and
I have used languages where this is expressible). I realize that
internally this is how Dialyzer works, but that does not mean the type
language must work his way.)
Without a firm definition, it's not possible to say how function specs
"should" be interpreted.
FWIW Dialyzer *can* (with -Wunderspecs) check the heterogeneous map
type-analogous case of a function returning a function. (i.e. it can
check that the returned function accepts at *least* the specified values;
just as with a heterogeneous map, we care whether it contains at *least*
the specified keys.)
> PS: Your MUA sends rich text in 12px.
*checks settings* Ah, it was set to "prefer text/reply with same
formatting". Fixed, thanks.
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