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class="noprint">From Wikibooks, open books for an open world</div> </div> <div id="contentSub"><div id="mw-content-subtitle"><div class="subpages">< <bdi dir="ltr"><a href="/wiki/Erlang_Programming" title="Erlang Programming">Erlang Programming</a></bdi></div></div></div> <div id="mw-content-text" class="mw-body-content"><div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr"><div class="mw-heading mw-heading2"><h2 id="Additional_Types">Additional Types</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Erlang_Programming/Additional_Types&veaction=edit&section=1" title="Edit section: Additional Types" class="mw-editsection-visualeditor"><span>edit</span></a><span class="mw-editsection-divider"> | </span><a href="/w/index.php?title=Erlang_Programming/Additional_Types&action=edit&section=1" title="Edit section's source code: Additional Types"><span>edit source</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>We have already seen the following types: tuple, list, integer, float, function and pid. We can check the type of an object by testing it. </p> <pre>1> is_pid( self() ). true </pre> <p>If you wish to convert between types, lists are the lingua franca of types in Erlang so make it a list first on your way to something else. Remember, type conversion is not a parallel-safe operation. </p><p>Some additional types are: port and reference. </p><p>A port is a connection to the external world. Typically ports generate and/or consume bit streams. Binary data is considered untyped data in Erlang. (See BitSyntax). </p><p>A reference is a globally unique symbol and is generated with: </p> <pre>19> make_ref(). #Ref<0.0.0.88> </pre> <p>A reference is only useful when a unique tag is needed across all connected processes. Do not confuse the term reference with a references in C, which points to data. An Erlang reference is only a unique tag. </p> <div class="mw-heading mw-heading3"><h3 id="Erlang_Has_No_Boolean_Type">Erlang Has No Boolean Type</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Erlang_Programming/Additional_Types&veaction=edit&section=2" title="Edit section: Erlang Has No Boolean Type" class="mw-editsection-visualeditor"><span>edit</span></a><span class="mw-editsection-divider"> | </span><a href="/w/index.php?title=Erlang_Programming/Additional_Types&action=edit&section=2" title="Edit section's source code: Erlang Has No Boolean Type"><span>edit source</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Erlang has no Boolean type. It has the atoms (true and false) which are generated by certain functions and expected by certain functions like guards and list comprehensions. The function: is_constant() generates either true or false. </p><p>We can test whether an object is a constant. </p> <pre>1> is_constant(a) true 2> is_atom(a). true </pre> <p>Because atoms are represented as constant numbers, atoms are constants. </p> <pre>is_constant(A). ** 1: variable 'A' is unbound ** 5> A=1. 1 6> is_constant(A). true </pre> <p>Theoretically, because the Boolean type is not built in, it should make it easier to let Erlang compute with alternate types of logic, {true, false, null} for instance. </p></div><noscript><img src="https://login.wikimedia.org/wiki/Special:CentralAutoLogin/start?type=1x1" alt="" width="1" height="1" style="border: none; position: absolute;"></noscript> <div class="printfooter" data-nosnippet="">Retrieved from "<a dir="ltr" href="https://en.wikibooks.org/w/index.php?title=Erlang_Programming/Additional_Types&oldid=3232913">https://en.wikibooks.org/w/index.php?title=Erlang_Programming/Additional_Types&oldid=3232913</a>"</div></div> <div id="catlinks" class="catlinks" data-mw="interface"><div id="mw-normal-catlinks" class="mw-normal-catlinks"><a href="/wiki/Special:Categories" title="Special:Categories">Category</a>: <ul><li><a href="/wiki/Category:Book:Erlang_Programming" title="Category:Book:Erlang Programming">Book:Erlang Programming</a></li></ul></div></div> </div> </main> </div> <div class="mw-footer-container"> <footer id="footer" class="mw-footer" > <ul id="footer-info"> <li id="footer-info-lastmod"> This page was last edited on 15 June 2017, at 00:41.</li> <li id="footer-info-copyright">Text is available under the <a rel="nofollow" class="external text" href="//creativecommons.org/licenses/by-sa/4.0/">Creative Commons Attribution-ShareAlike License</a>; additional terms may apply. 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