diff options
Diffstat (limited to 'system/doc/reference_manual/modules.xml')
| -rw-r--r-- | system/doc/reference_manual/modules.xml | 199 |
1 files changed, 114 insertions, 85 deletions
diff --git a/system/doc/reference_manual/modules.xml b/system/doc/reference_manual/modules.xml index f0ec7ef165..5f2ac2a67d 100644 --- a/system/doc/reference_manual/modules.xml +++ b/system/doc/reference_manual/modules.xml @@ -4,20 +4,21 @@ <chapter> <header> <copyright> - <year>2003</year><year>2014</year> + <year>2003</year><year>2015</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/. + Licensed under the Apache License, Version 2.0 (the "License"); + you may not use this file except in compliance with the License. + You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 - 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. + Unless required by applicable law or agreed to in writing, software + distributed under the License is distributed on an "AS IS" BASIS, + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + See the License for the specific language governing permissions and + limitations under the License. </legalnotice> @@ -33,7 +34,8 @@ <title>Module Syntax</title> <p>Erlang code is divided into <em>modules</em>. A module consists of a sequence of attributes and function declarations, each - terminated by period (.). Example:</p> + terminated by period (.).</p> + <p><em>Example:</em></p> <pre> -module(m). % module attribute -export([fact/1]). % module attribute @@ -42,50 +44,52 @@ fact(N) when N>0 -> % beginning of function declaration N * fact(N-1); % | fact(0) -> % | 1. % end of function declaration</pre> - <p>See the <seealso marker="functions">Functions</seealso> chapter - for a description of function declarations.</p> + <p>For a description of function declarations, see + <seealso marker="functions">Function Declaration Syntax</seealso>.</p> </section> <section> <title>Module Attributes</title> <p>A <em>module attribute</em> defines a certain property of a - module. A module attribute consists of a tag and a value.</p> + module.</p> + <p>A module attribute consists of a tag and a value:</p> <pre> -Tag(Value).</pre> <p><c>Tag</c> must be an atom, while <c>Value</c> must be a literal term. As a convenience in user-defined attributes, if the literal term <c>Value</c> has the syntax <c>Name/Arity</c> (where <c>Name</c> is an atom and <c>Arity</c> a positive integer), - the term <c>Name/Arity</c> will be translated to <c>{Name,Arity}</c>.</p> + the term <c>Name/Arity</c> is translated to <c>{Name,Arity}</c>.</p> <p>Any module attribute can be specified. The attributes are stored in the compiled code and can be retrieved by calling - <c>Module:module_info(attributes)</c> or by using - <seealso marker="stdlib:beam_lib#chunks/2">beam_lib(3)</seealso>.</p> + <c>Module:module_info(attributes)</c>, or by using the module + <seealso marker="stdlib:beam_lib#chunks/2">beam_lib(3)</seealso> + in STDLIB.</p> - <p>There are several module attributes with predefined meanings, - some of which have arity two, but user-defined module + <p>Several module attributes have predefined meanings. + Some of them have arity two, but user-defined module attributes must have arity one.</p> <section> <title>Pre-Defined Module Attributes</title> - <p>Pre-defined module attributes should be placed before any + <p>Pre-defined module attributes is to be placed before any function declaration.</p> <taglist> <tag><c>-module(Module).</c></tag> <item> <p>Module declaration, defining the name of the module. - The name <c>Module</c>, an atom, should be the same as - the file name minus the extension <c>erl</c>. Otherwise - <seealso marker="code_loading#loading">code loading</seealso> will + The name <c>Module</c>, an atom, is to be same as + the file name minus the extension <c>.erl</c>. Otherwise + <seealso marker="code_loading#loading">code loading</seealso> does not work as intended.</p> - <p>This attribute should be specified first and is the only - attribute which is mandatory.</p> + <p>This attribute is to be specified first and is the only + mandatory attribute.</p> </item> <tag><c>-export(Functions).</c></tag> <item> - <p>Exported functions. Specifies which of the functions - defined within the module that are visible outside + <p>Exported functions. Specifies which of the functions, + defined within the module, that are visible from outside the module.</p> <p><c>Functions</c> is a list <c>[Name1/Arity1, ..., NameN/ArityN]</c>, where each @@ -93,32 +97,37 @@ fact(0) -> % | </item> <tag><c>-import(Module,Functions).</c></tag> <item> - <p>Imported functions. Imported functions can be called - the same way as local functions, that is without any module + <p>Imported functions. Can be called + the same way as local functions, that is, without any module prefix.</p> <p><c>Module</c>, an atom, specifies which module to import functions from. <c>Functions</c> is a list similar as for - <c>export</c> above.</p> + <c>export</c>.</p> </item> <tag><c>-compile(Options).</c></tag> <item> - <p>Compiler options. <c>Options</c>, which is a single option - or a list of options, will be added to the option list when - compiling the module. See <c>compile(3)</c>.</p> + <p>Compiler options. <c>Options</c> is a single option + or a list of options. + This attribute is added to the option list when + compiling the module. See the <seealso marker="compiler:compile"> + compile(3)</seealso> manual page in Compiler.</p> </item> <tag><c>-vsn(Vsn).</c></tag> <item> <p>Module version. <c>Vsn</c> is any literal term and can be - retrieved using <c>beam_lib:version/1</c>, see - <seealso marker="stdlib:beam_lib#version/1">beam_lib(3)</seealso>.</p> + retrieved using <c>beam_lib:version/1</c>, see the + <seealso marker="stdlib:beam_lib#version/1">beam_lib(3)</seealso> + manual page in STDLIB.</p> <p>If this attribute is not specified, the version defaults to the MD5 checksum of the module.</p> </item> <tag><c>-on_load(Function).</c></tag> <item> - <p>Names a function that should be run automatically when a - module a loaded. See <seealso marker="code_loading#on_load"> - code loading</seealso> for more information.</p> + <p>This attribute names a function that is to be run + automatically when a + module is loaded. For more information, see + <seealso marker="code_loading#on_load"> + Running a Function When a Module is Loaded</seealso>.</p> </item> </taglist> </section> @@ -130,9 +139,14 @@ fact(0) -> % | <pre> -behaviour(Behaviour).</pre> <p>The atom <c>Behaviour</c> gives the name of the behaviour, - which can be a user defined behaviour or one of the OTP - standard behaviours <c>gen_server</c>, <c>gen_fsm</c>, - <c>gen_event</c> or <c>supervisor</c>.</p> + which can be a user-defined behaviour or one of the following OTP + standard behaviours:</p> + <list type="bulleted"> + <item><c>gen_server</c></item> + <item><c>gen_fsm</c></item> + <item><c>gen_event</c></item> + <item><c>supervisor</c></item> + </list> <p>The spelling <c>behavior</c> is also accepted.</p> <p>The callback functions of the module can be specified either directly by the exported function <c>behaviour_info/1</c>:</p> @@ -142,7 +156,7 @@ behaviour_info(callbacks) -> Callbacks.</pre> function:</p> <pre> -callback Name(Arguments) -> Result.</pre> - <p>where <c>Arguments</c> is a list of zero or more arguments. + <p>Here, <c>Arguments</c> is a list of zero or more arguments. The <c>-callback</c> attribute is to be preferred since the extra type information can be used by tools to produce documentation or find discrepancies.</p> @@ -153,7 +167,7 @@ behaviour_info(callbacks) -> Callbacks.</pre> <section> <title>Record Definitions</title> - <p>The same syntax as for module attributes is used by + <p>The same syntax as for module attributes is used for record definitions:</p> <pre> -record(Record,Fields).</pre> @@ -163,7 +177,7 @@ behaviour_info(callbacks) -> Callbacks.</pre> </section> <section> - <title>The Preprocessor</title> + <title>Preprocessor</title> <p>The same syntax as for module attributes is used by the preprocessor, which supports file inclusion, macros, and conditional compilation:</p> @@ -171,7 +185,7 @@ behaviour_info(callbacks) -> Callbacks.</pre> -include("SomeFile.hrl"). -define(Macro,Replacement).</pre> - <p>Read more in <seealso marker="macros">The Preprocessor</seealso>.</p> + <p>Read more in <seealso marker="macros">Preprocessor</seealso>.</p> </section> <section> @@ -180,110 +194,125 @@ behaviour_info(callbacks) -> Callbacks.</pre> changing the pre-defined macros <c>?FILE</c> and <c>?LINE</c>:</p> <pre> -file(File, Line).</pre> - <p>This attribute is used by tools such as Yecc to inform the - compiler that the source program was generated by another tool - and indicates the correspondence of source files to lines of - the original user-written file from which the source program - was produced.</p> + <p>This attribute is used by tools, such as Yecc, to inform the + compiler that the source program is generated by another tool. + It also indicates the correspondence of source files to lines of + the original user-written file, from which the source program + is produced.</p> </section> <section> <title>Types and function specifications</title> <p>A similar syntax as for module attributes is used for - specifying types and function specifications. + specifying types and function specifications: </p> <pre> -type my_type() :: atom() | integer(). --spec my_function(integer()) -> integer(). - </pre> +-spec my_function(integer()) -> integer().</pre> <p>Read more in <seealso marker="typespec">Types and Function specifications</seealso>. </p> <p> The description is based on <url href="http://www.erlang.org/eeps/eep-0008.html">EEP8 - - Types and function specifications</url> - which will not be further updated. + Types and function specifications</url>, + which is not to be further updated. </p> </section> </section> <section> <title>Comments</title> - <p>Comments may be placed anywhere in a module except within strings - and quoted atoms. The comment begins with the character "%", + <p>Comments can be placed anywhere in a module except within strings + and quoted atoms. A comment begins with the character "%", continues up to, but does not include the next end-of-line, and - has no effect. Note that the terminating end-of-line has + has no effect. Notice that the terminating end-of-line has the effect of white space.</p> </section> <section> - <title>The module_info/0 and module_info/1 functions</title> + <title>module_info/0 and module_info/1 functions</title> <p>The compiler automatically inserts the two special, exported - functions into each module: <c>Module:module_info/0</c> and - <c>Module:module_info/1</c>. These functions can be called to - retrieve information about the module.</p> + functions into each module:</p> + <list type="bulleted"> + <item><c>Module:module_info/0</c></item> + <item><c>Module:module_info/1</c></item> + </list> + <p>These functions can be called to retrieve information + about the module.</p> <section> <title>module_info/0</title> - <p>The <c>module_info/0</c> function in each module returns + <p>The <c>module_info/0</c> function in each module, returns a list of <c>{Key,Value}</c> tuples with information about the module. Currently, the list contain tuples with the following - <c>Key</c>s: <c>attributes</c>, <c>compile</c>, - <c>exports</c>, and <c>imports</c>. The order and number of tuples + <c>Key</c>s: <c>module</c>, <c>attributes</c>, <c>compile</c>, + <c>exports</c>, <c>md5</c> and <c>native</c>. + The order and number of tuples may change without prior notice.</p> - - <warning><p>The <c>{imports,Value}</c> tuple may be removed in a future - release because <c>Value</c> is always an empty list. - Do not write code that depends on it being present.</p></warning> </section> <section> <title>module_info/1</title> - <p>The call <c>module_info(Key)</c>, where key is an atom, + <p>The call <c>module_info(Key)</c>, where <c>Key</c> is an atom, returns a single piece of information about the module.</p> <p>The following values are allowed for <c>Key</c>:</p> <taglist> + <tag><c>module</c></tag> + <item> + <p>Returns an atom representing the module name.</p> + </item> + <tag><c>attributes</c></tag> <item> - <p>Return a list of <c>{AttributeName,ValueList}</c> tuples, + <p>Returns a list of <c>{AttributeName,ValueList}</c> tuples, where <c>AttributeName</c> is the name of an attribute, - and <c>ValueList</c> is a list of values. Note: a given - attribute may occur more than once in the list with different + and <c>ValueList</c> is a list of values. Notice that a given + attribute can occur more than once in the list with different values if the attribute occurs more than once in the module.</p> - <p>The list of attributes will be empty if - the module has been stripped with - <seealso marker="stdlib:beam_lib#strip/1">beam_lib(3)</seealso>.</p> + <p>The list of attributes becomes empty if + the module is stripped with the + <seealso marker="stdlib:beam_lib#strip/1">beam_lib(3)</seealso> + module (in STDLIB).</p> </item> <tag><c>compile</c></tag> <item> - <p>Return a list of tuples containing information about - how the module was compiled. This list will be empty if - the module has been stripped with - <seealso marker="stdlib:beam_lib#strip/1">beam_lib(3)</seealso>.</p> + <p>Returns a list of tuples with information about + how the module was compiled. This list is empty if + the module has been stripped with the + <seealso marker="stdlib:beam_lib#strip/1">beam_lib(3)</seealso> + module (in STDLIB).</p> </item> - <tag><c>imports</c></tag> + <tag><c>md5</c></tag> <item> - <p>Always return an empty list. The <c>imports</c> key may not - be supported in future release.</p> + <p>Returns a binary representing the MD5 checksum of the module. + If the module has native code loaded, this will be the MD5 of the + native code, not the BEAM bytecode.</p> </item> <tag><c>exports</c></tag> <item> - <p>Return a list of <c>{Name,Arity}</c> tuples with + <p>Returns a list of <c>{Name,Arity}</c> tuples with all exported functions in the module.</p> </item> <tag><c>functions</c></tag> <item> - <p>Return a list of <c>{Name,Arity}</c> tuples with + <p>Returns a list of <c>{Name,Arity}</c> tuples with all functions in the module.</p> </item> + + <tag><c>native</c></tag> + <item> + <p>Return <c>true</c> if the module has native compiled code. + Return <c>false</c> otherwise. In a system compiled without HiPE + support, the result is always <c>false</c></p> + </item> </taglist> </section> </section> |