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diff --git a/system/doc/reference_manual/data_types.xml b/system/doc/reference_manual/data_types.xml new file mode 100644 index 0000000000..c85ac44165 --- /dev/null +++ b/system/doc/reference_manual/data_types.xml @@ -0,0 +1,399 @@ +<?xml version="1.0" encoding="latin1" ?> +<!DOCTYPE chapter SYSTEM "chapter.dtd"> + +<chapter> + <header> + <copyright> + <year>2003</year><year>2009</year> + <holder>Ericsson AB. All Rights Reserved.</holder> + </copyright> + <legalnotice> + The contents of this file are subject to the Erlang Public License, + Version 1.1, (the "License"); you may not use this file except in + compliance with the License. You should have received a copy of the + Erlang Public License along with this software. If not, it can be + retrieved online at http://www.erlang.org/. + + Software distributed under the License is distributed on an "AS IS" + basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See + the License for the specific language governing rights and limitations + under the License. + + </legalnotice> + + <title>Data Types</title> + <prepared></prepared> + <docno></docno> + <date></date> + <rev></rev> + <file>data_types.xml</file> + </header> + + <section> + <title>Terms</title> + <p>Erlang provides a number of data types which are listed in this + chapter. A piece of data of any data type is called a + <em>term</em>.</p> + </section> + + <section> + <title>Number</title> + <p>There are two types of numeric literals, <em>integers</em> and + <em>floats</em>. Besides the conventional notation, there are two + Erlang-specific notations:</p> + <list type="bulleted"> + <item><c>$</c><em><c>char</c></em> <br></br> + + ASCII value of the character <em><c>char</c></em>.</item> + <item><em><c>base</c></em><c>#</c><em><c>value</c></em> <br></br> + + Integer with the base <em><c>base</c></em>, which must be an + integer in the range 2..36. <br></br> + + In Erlang 5.2/OTP R9B and earlier versions, the allowed range + is 2..16.</item> + </list> + <p>Examples:</p> + <pre> +1> <input>42.</input> +42 +2> <input>$A.</input> +65 +3> <input>$\ .</input> +10 +4> <input>2#101.</input> +5 +5> <input>16#1f.</input> +31 +6> <input>2.3.</input> +2.3 +7> <input>2.3e3.</input> +2.3e3 +8> <input>2.3e-3.</input> +0.0023</pre> + </section> + + <section> + <title>Atom</title> + <p>An atom is a literal, a constant with name. An atom should be + enclosed in single quotes (') if it does not begin with a + lower-case letter or if it contains other characters than + alphanumeric characters, underscore (_), or @.</p> + <p>Examples:</p> + <pre> +hello +phone_number +'Monday' +'phone number'</pre> + </section> + + <section> + <title>Bit Strings and Binaries</title> + <p>A bit string is used to store an area of untyped memory.</p> + <p>Bit Strings are expressed using the + <seealso marker="expressions#bit_syntax">bit syntax</seealso>.</p> + <p>Bit Strings which consists of a number of bits which is evenly + divisible by eight are called Binaries</p> + <p>Examples:</p> + <pre> +1> <input><<10,20>>.</input> +<<10,20>> +2> <input><<"ABC">>.</input> +<<"ABC">> +1> <input><<1:1,0:1>>.</input> +<<2:2>></pre> + <p>More examples can be found in Programming Examples.</p> + </section> + + <section> + <title>Reference</title> + <p>A reference is a term which is unique in an Erlang runtime + system, created by calling <c>make_ref/0</c>.</p> + </section> + + <section> + <title>Fun</title> + <p>A fun is a functional object. Funs make it possible to create + an anonymous function and pass the function itself -- not its + name -- as argument to other functions.</p> + <p>Example:</p> + <pre> +1> <input>Fun1 = fun (X) -> X+1 end.</input> +#Fun<erl_eval.6.39074546> +2> <input>Fun1(2).</input> +3</pre> + <p>Read more about funs in <seealso marker="expressions#funs">Fun Expressions</seealso>. More examples can be found in Programming + Examples.</p> + </section> + + <section> + <title>Port Identifier</title> + <p>A port identifier identifies an Erlang port. <c>open_port/2</c>, + which is used to create ports, will return a value of this type.</p> + <p>Read more about ports in <seealso marker="ports">Ports and Port Drivers</seealso>.</p> + </section> + + <section> + <title>Pid</title> + <p>A process identifier, pid, identifies a process. + <c>spawn/1,2,3,4</c>, <c>spawn_link/1,2,3,4</c> and + <c>spawn_opt/4</c>, which are used to create processes, return + values of this type. Example:</p> + <pre> +1> <input>spawn(m, f, []).</input> +<0.51.0></pre> + <p>The BIF <c>self()</c> returns the pid of the calling process. + Example:</p> + <pre> +-module(m). +-export([loop/0]). + +loop() -> + receive + who_are_you -> + io:format("I am ~p~n", [self()]), + loop() + end. + +1> <input>P = spawn(m, loop, []).</input> +<0.58.0> +2> <input>P ! who_are_you.</input> +I am <0.58.0> +who_are_you</pre> + <p>Read more about processes in + <seealso marker="processes">Processes</seealso>.</p> + </section> + + <section> + <title>Tuple</title> + <p>Compound data type with a fixed number of terms:</p> + <pre> +{Term1,...,TermN}</pre> + <p>Each term <c>Term</c> in the tuple is called an + <em>element</em>. The number of elements is said to be + the <em>size</em> of the tuple.</p> + <p>There exists a number of BIFs to manipulate tuples.</p> + <p>Examples:</p> + <pre> +1> <input>P = {adam,24,{july,29}}.</input> +{adam,24,{july,29}} +2> <input>element(1,P).</input> +adam +3> <input>element(3,P).</input> +{july,29} +4> <input>P2 = setelement(2,P,25).</input> +{adam,25,{july,29}} +5> <input>tuple_size(P).</input> +3 +6> <input>tuple_size({}).</input> +0</pre> + </section> + + <section> + <title>List</title> + <p>Compound data type with a variable number of terms.</p> + <pre> +[Term1,...,TermN]</pre> + <p>Each term <c>Term</c> in the list is called an + <em>element</em>. The number of elements is said to be + the <em>length</em> of the list.</p> + <p>Formally, a list is either the empty list <c>[]</c> or + consists of a <em>head</em> (first element) and a <em>tail</em> + (remainder of the list) which is also a list. The latter can + be expressed as <c>[H|T]</c>. The notation + <c>[Term1,...,TermN]</c> above is actually shorthand for + the list <c>[Term1|[...|[TermN|[]]]]</c>.</p> + <p>Example: <br></br> +<c>[]</c> is a list, thus <br></br> +<c>[c|[]]</c> is a list, thus <br></br> +<c>[b|[c|[]]]</c> is a list, thus <br></br> +<c>[a|[b|[c|[]]]]</c> is a list, or in short <c>[a,b,c]</c>.</p> + <p></p> + <p>A list where the tail is a list is sometimes called a <em>proper list</em>. It is allowed to have a list where the tail is not a + list, for example <c>[a|b]</c>. However, this type of list is of + little practical use.</p> + <p>Examples:</p> + <pre> +1> <input>L1 = [a,2,{c,4}].</input> +[a,2,{c,4}] +2> <input>[H|T] = L1.</input> +[a,2,{c,4}] +3> <input>H.</input> +a +4> <input>T.</input> +[2,{c,4}] +5> <input>L2 = [d|T].</input> +[d,2,{c,4}] +6> <input>length(L1).</input> +3 +7> <input>length([]).</input> +0</pre> + <p>A collection of list processing functions can be found in + the STDLIB module <c>lists</c>.</p> + </section> + + <section> + <title>String</title> + <p>Strings are enclosed in double quotes ("), but is not a + data type in Erlang. Instead a string <c>"hello"</c> is + shorthand for the list <c>[$h,$e,$l,$l,$o]</c>, that is + <c>[104,101,108,108,111]</c>.</p> + <p>Two adjacent string literals are concatenated into one. This is + done at compile-time and does not incur any runtime overhead. + Example:</p> + <pre> +"string" "42"</pre> + <p>is equivalent to</p> + <pre> +"string42"</pre> + </section> + + <section> + <title>Record</title> + <p>A record is a data structure for storing a fixed number of + elements. It has named fields and is similar to a struct in C. + However, record is not a true data type. Instead record + expressions are translated to tuple expressions during + compilation. Therefore, record expressions are not understood by + the shell unless special actions are taken. See <c>shell(3)</c> + for details.</p> + <p>Examples:</p> + <pre> +-module(person). +-export([new/2]). + +-record(person, {name, age}). + +new(Name, Age) -> + #person{name=Name, age=Age}. + +1> <input>person:new(ernie, 44).</input> +{person,ernie,44}</pre> + <p>Read more about records in + <seealso marker="records">Records</seealso>. More examples can be + found in Programming Examples.</p> + </section> + + <section> + <title>Boolean</title> + <p>There is no Boolean data type in Erlang. Instead the atoms + <c>true</c> and <c>false</c> are used to denote Boolean values.</p> + <p>Examples:</p> + <pre> +1> <input>2 =< 3</input>. +true +2> <input>true or false</input>. +true</pre> + </section> + + <section> + <title>Escape Sequences</title> + <p>Within strings and quoted atoms, the following escape sequences + are recognized:</p> + <table> + <row> + <cell align="left" valign="middle"><em>Sequence</em></cell> + <cell align="left" valign="middle"><em>Description</em></cell> + </row> + <row> + <cell align="left" valign="middle">\\b</cell> + <cell align="left" valign="middle">backspace</cell> + </row> + <row> + <cell align="left" valign="middle">\\d</cell> + <cell align="left" valign="middle">delete</cell> + </row> + <row> + <cell align="left" valign="middle">\\e</cell> + <cell align="left" valign="middle">escape</cell> + </row> + <row> + <cell align="left" valign="middle">\\f</cell> + <cell align="left" valign="middle">form feed</cell> + </row> + <row> + <cell align="left" valign="middle">\</cell> + <cell align="left" valign="middle">newline</cell> + </row> + <row> + <cell align="left" valign="middle">\\r</cell> + <cell align="left" valign="middle">carriage return</cell> + </row> + <row> + <cell align="left" valign="middle">\\s</cell> + <cell align="left" valign="middle">space</cell> + </row> + <row> + <cell align="left" valign="middle">\\t</cell> + <cell align="left" valign="middle">tab</cell> + </row> + <row> + <cell align="left" valign="middle">\\v</cell> + <cell align="left" valign="middle">vertical tab</cell> + </row> + <row> + <cell align="left" valign="middle">\\XYZ, \\YZ, \\Z</cell> + <cell align="left" valign="middle">character with octal representation XYZ, YZ or Z</cell> + </row> + <row> + <cell align="left" valign="middle">\\xXY</cell> + <cell align="left" valign="middle">character with hexadecimal representation XY</cell> + </row> + <row> + <cell align="left" valign="middle">\\x{X...}</cell> + <cell align="left" valign="middle">character with hexadecimal representation; X... is one or more hexadecimal characters</cell> + </row> + <row> + <cell align="left" valign="middle">\\^a...\\^z <br></br> +\\^A...\\^Z</cell> + <cell align="left" valign="middle">control A to control Z</cell> + </row> + <row> + <cell align="left" valign="middle">\\'</cell> + <cell align="left" valign="middle">single quote</cell> + </row> + <row> + <cell align="left" valign="middle">\\"</cell> + <cell align="left" valign="middle">double quote</cell> + </row> + <row> + <cell align="left" valign="middle">\\\\</cell> + <cell align="left" valign="middle">backslash</cell> + </row> + <tcaption>Recognized Escape Sequences.</tcaption> + </table> + </section> + + <section> + <title>Type Conversions</title> + <p>There are a number of BIFs for type conversions. Examples:</p> + <pre> +1> <input>atom_to_list(hello).</input> +"hello" +2> <input>list_to_atom("hello").</input> +hello +3> <input>binary_to_list(<<"hello">>).</input> +"hello" +4> <input>binary_to_list(<<104,101,108,108,111>>).</input> +"hello" +5> <input>list_to_binary("hello").</input> +<<104,101,108,108,111>> +6> <input>float_to_list(7.0).</input> +"7.00000000000000000000e+00" +7> <input>list_to_float("7.000e+00").</input> +7.0 +8> <input>integer_to_list(77).</input> +"77" +9> <input>list_to_integer("77").</input> +77 +10> <input>tuple_to_list({a,b,c}).</input> +[a,b,c] +11> <input>list_to_tuple([a,b,c]).</input> +{a,b,c} +12> <input>term_to_binary({a,b,c}).</input> +<<131,104,3,100,0,1,97,100,0,1,98,100,0,1,99>> +13> <input>binary_to_term(<<131,104,3,100,0,1,97,100,0,1,98,100,0,1,99>>).</input> +{a,b,c}</pre> + </section> +</chapter> + |