[erlang-questions] Current function undefined as displayed by i().

Trond Endrestøl Trond.Endrestol@REDACTED
Thu Dec 3 12:32:51 CET 2015


I'm new to the list and new to Erlang.

I'm running:

FreeBSD 10.2-STABLE #0 r291578: Tue Dec  1 14:32:16 CET 2015 amd64

Erlang is erlang-18.1.5,3 from FreeBSD's ports collection 

Erlang/OTP 18 [erts-7.1] [source] [64-bit] [smp:4:4] [async-threads:10] [hipe] [kernel-poll:true] [dtrace]
Eshell V7.1

I came across a puzzle:

I have an Erlang process spawned with a function of arity 0.
Running the shell command i() gives this (abbreviated) output.

Pid                   Initial Call                          Heap     Reds Msgs
Registered            Current Function                     Stack
<0.42.0>              mathserver:loop/0                      987    10679    0
mathserver            undefined                                0

Here's start/0 from my module mathserver:

start() ->
    Pid = erlang:spawn(?MODULE, loop, []),
    erlang:register(?MODULE, Pid),      % Local name register
    global:register_name(?MODULE, Pid). % Global name register

loop/0 in this module consists mainly of a receive statement, spawning 
new processes when it recognises a particular message.

While googling for "erlang current function undefined", I tried the 
sample code from 

I made some slight modifications to the code, limited to a better 
module name, the use of the ?MODULE macro as appropriate, and a call 
to global:register_name/2.

In this case the bcast_server:process_request/1 is spawned with an 
empty list in the argument list, i.e. [[]].

start() ->
    ServerPid = erlang:spawn(?MODULE, process_requests, [ [] ]),
    erlang:register(?MODULE, ServerPid),
    global:register_name(?MODULE, ServerPid).

Running i() produces this (abbreviated) output:

Pid                   Initial Call                          Heap     Reds Msgs
Registered            Current Function                     Stack
<0.57.0>              bcast_server:process_requests/1        233        1    0
bcast_server          bcast_server:process_requests/1          3

process_requests/1 is similar to my own loop/0. The only difference is 
arity of 0 versus arity of 1, i.e. non-zero.

A named Erlang node bears no difference from an anonymous Erlang node.

Can someone please explain why "current function" is undefined in one 
instance and defined in another?

Trond Endrestøl                     |     Trond.Endrestol@REDACTED
ACM, NAS, NUUG, SAGE, USENIX        |     FreeBSD 10.2-S & Alpine 2.20

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