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< Erlang ~ Creating a function that doesn't do anything |
| wolfgke |
 Posted: Sun Sep 16, 2007 10:35 am |
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User
Joined: 16 Sep 2007
Posts: 16
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Dear people,
I'm trying to learn Erlang at the moment. I got into the following problem:
Let's explain it like this:
The function initProcessesLoop has one parameter: a list of PIDs.
If the lists contains more than one item the (more complicated) function definition is to be used: a special message is sent to the first process in the list.
This definition seems to work.
But when only one item exits: how can I tell Erlang that it should NOT do anything:
Code: initProcessesLoop([_]);
does not work.
And
Code: initProcessesLoop([_]) -> 0;
returns 0 (but I don't want the function to return anything).
What is the typical way to do so in Erlang? |
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| Mazen |
| Posted: Sun Sep 16, 2007 2:56 pm |
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Joined: 20 Jul 2006
Posts: 164
Location: London
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Hiya,
May I ask why you want it to return nothing? Since function calls are sequential, the only way to "not returning" is to spawn of a process that potentially does something (or nothing).
In other words, as far as I know it is not possible to create a function wich does not return something. Are you handling the return value from this function? If not, then you can just return anything. |
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| wolfgke |
| Posted: Mon Sep 17, 2007 7:00 pm |
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Joined: 16 Sep 2007
Posts: 16
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The reason why I don't want to return anything is simply that no return value is necessary. So: why should I be forced to do so?
I got my program to work by letting the function return something. But I still think this is not an elegant way.
---
For explaination:
The functions gets a list of processes PIDs as parameter and sends each processes (except the last one) a special message which tells them what the next process in the list is.
So the code looks like this:
Code:
initProcessesLoop([_]) -> {ok, initProcessesLoop};
initProcessesLoop([FirstPid, NextPid|PidTail]) ->
FirstPid ! {init, NextPid},
initProcessesLoop([NextPid|PidTail]).
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| francesco |
| Posted: Mon Sep 17, 2007 7:39 pm |
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Joined: 07 Jul 2006
Posts: 249
Location: London
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Quote: The reason why I don't want to return anything is simply that no return value is necessary. So: why should I be forced to do so?
Erlang has its origins in Functional Programming. A function has to always return a value, even if it is ignored by the caller of the function. This is fundamental to FP.
What you usually do when you are not interested in the return value is to send back the atom ok.
Francesco
--
http://www.erlang-consulting.com |
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| wolfgke |
| Posted: Tue Sep 18, 2007 12:07 pm |
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Joined: 16 Sep 2007
Posts: 16
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Thanks to everybody for the explanations.  |
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