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POUnable to use function call in function guard
 

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    <p>I'm new to Erlang and am trying to program a bounded-buffer problem program. It is almost working, except for making sure the producers don't get too far ahead and overwrite unconsumed data. To handle this, I decided to try putting guards on my buffer() function so that I could have a version w/o receive used when the buffer is full, a version w/o send used when the buffer is empty, and a normal version for the rest of the time.</p> <p>My problem is that the guard for the receiver-less version requires me to know the size of the array representing the buffer, which requires a call to <code>array:size/1</code>. Apparently, Erlang does not allow function invocations in guards, which prevents this from working. Is there some way to work around this without changing the function declaration for my buffer actor?</p> <pre><code>%% buffer: array num num %% A process that holds the shared buffer for the producers and consumers buffer(Buf, NextWrite, NextRead) when NextWrite == NextRead -&gt; io:format(" * ~w, ~w, ~w~n", [array:to_list(Buf), NextRead, NextWrite]), receive {enqueue, Reply_Pid, Num} -&gt; io:format("~w: &gt; ~w~n", [Reply_Pid, Num]), buffer(array:set(NextWrite rem array:size(Buf), Num, Buf), NextWrite + 1, NextRead); finish -&gt; io:format("finished printing~n") end; buffer(Buf, NextWrite, NextRead) when (NextWrite - NextRead) == array:size(Buf) -&gt; io:format(" * ~w, ~w, ~w~n", [array:to_list(Buf), NextRead, NextWrite]), receive {dequeue, Reply_Pid} -&gt; io:format("~w: &lt; ~w~n", [Reply_Pid, array:get(NextRead rem array:size(Buf), Buf)]), Reply_Pid ! {reply, array:get(NextRead rem array:size(Buf), Buf)}, buffer(Buf, NextWrite, NextRead + 1); finish -&gt; io:format("finished printing~n") end; buffer(Buf, NextWrite, NextRead) -&gt; io:format(" * ~w, ~w, ~w~n", [array:to_list(Buf), NextRead, NextWrite]), receive {dequeue, Reply_Pid} -&gt; io:format("~w: &lt; ~w~n", [Reply_Pid, array:get(NextRead rem array:size(Buf), Buf)]), Reply_Pid ! {reply, array:get(NextRead rem array:size(Buf), Buf)}, buffer(Buf, NextWrite, NextRead + 1); {enqueue, Reply_Pid, Num} -&gt; io:format("~w: &gt; ~w~n", [Reply_Pid, Num]), buffer(array:set(NextWrite rem array:size(Buf), Num, Buf), NextWrite + 1, NextRead); finish -&gt; io:format("finished printing~n") end. </code></pre>
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