[erlang-questions] Dialyzer and rpc:pmap

[Gustav Simonsson]

In Erlang function specifications term() is equivalent with any() which contains the set of all Erlang terms, including the atom 'timeout'.

Looking at the internal rpc function calls from pmap/3, we see that in the end do_yield/2 can return the atom timeout.
However, since do_yield/2 is called as do_yield(Key, infinity) the receive clause in do_yield/2 shouldn't be able to return timeout in the case of calling pmap/3.

Does dialyzer infer that the receive clause in do_yield will wait indefinitely for a matching message in this case, or does it think that a timeout can occur, and therefore include the timeout atom as a possible return value?

Regards,
Gustav Simonsson

----- Original Message -----
From: "Bernie Duggan" <bernie@REDACTED>
To: "Erlang Questions" <erlang-questions@REDACTED>
Sent: Wednesday, August 31, 2011 8:00:26 AM
Subject: [erlang-questions] Dialyzer and rpc:pmap


Hi all (Hi dialyzer people especially :)) 

I have been having a heated debate with dialyzer over the return value of rpc:pmap/3. The following code demonstrates the issue: 

---------------------------------------------- 
-module(dialyzer_test). 

-export([run/0, f/1]). 

run() -> 
A = [{a, a}, {b, b}], 
B = [X || {a, X} <- A], 

C = rpc:pmap({?MODULE, f}, [], A), 
D = [X || {a, X} <- C], 
{B, D}. 

f(X) -> X. 
---------------------------------------------- 

Basically I have a list, A, and an rpc:pmap call to the identity function with A as the list - this quite correctly returns A (stored in C). Next, I run a filter list comprehension over A and C to grab just the tuples with 'a' as their first element. The code all works fine (returning {[a], [a]}) but dialyzer complains: 

dialyzer_test.erl:10: The pattern [{'a', X} | _] can never match the type ['timeout' | {'value',_}] 

Line 10 is the "D =..." line. It looks like the return value of rpc:pmap is being inferred incorrectly, but the -spec for it in rpc.erl gives the return type as [term()] which is what I'd expect. 

Any hints? Something obvious I've missed? 

Cheers, 

Bernard 

_______________________________________________
erlang-questions mailing list
erlang-questions@REDACTED
http://erlang.org/mailman/listinfo/erlang-questions