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<erlref>
  <header>
    <copyright>
      <year>1998</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>int</title>
    <prepared></prepared>
    <docno></docno>
    <date></date>
    <rev></rev>
  </header>
  <module>int</module>
  <modulesummary>Interpreter Interface</modulesummary>
  <description>
    <p>The Erlang interpreter provides mechanisms for breakpoints and
      stepwise execution of code. It is mainly intended to be used by
      the <em>Debugger</em>, see Debugger User's Guide and
      <c>debugger(3)</c>.</p>
    
    <p>From the shell, it is possible to:</p>
    <list>
      <item>Specify which modules should be interpreted.</item>
      <item>Specify breakpoints.</item>
      <item>Monitor the current status of all processes executing code
	in interpreted modules, also processes at other Erlang nodes.
      </item>
    </list>

    <p>By <em>attaching to</em> a process executing interpreted code, it
      is possible to examine variable bindings and order stepwise
      execution. This is done by sending and receiving information
      to/from the process via a third process, called the meta process.
      It is possible to implement your own attached process. See
      <c>int.erl</c> for available functions and <c>dbg_ui_trace.erl</c>
      for possible messages.</p>

    <p>The interpreter depends on the Kernel, STDLIB and GS
      applications, which means modules belonging to any of these
      applications are not allowed to be interpreted as it could lead
      to a deadlock or emulator crash. This also applies to modules
      belonging to the Debugger application itself.</p>
  </description>

  <section>
    <title>Breakpoints</title>

    <p>Breakpoints are specified on a line basis. When a process
      executing code in an interpreted module reaches a breakpoint, it
      will stop. This means that that a breakpoint must be set at an
      executable line, that is, a line of code containing an executable
      expression.</p>

    <p>A breakpoint have a status, a trigger action and may have a
      condition associated with it. The status is either <em>active</em>
      or <em>inactive</em>. An inactive breakpoint is ignored. When a
      breakpoint is reached, the trigger action specifies if
      the breakpoint should continue to be active (<em>enable</em>), if
      it should become inactive (<em>disable</em>), or if it should be
      removed (<em>delete</em>). A condition is a tuple
      <c>{Module,Name}</c>. When the breakpoint is reached,
      <c>Module:Name(Bindings)</c> is called. If this evaluates to
      <c>true</c>, execution will stop. If this evaluates to
      <c>false</c>, the breakpoint is ignored. <c>Bindings</c> contains
      the current variable bindings, use <c>get_binding</c> to retrieve
      the value for a given variable.</p>

    <p>By default, a breakpoint is active, has trigger action
      <c>enable</c> and has no condition associated with it. For more
      detailed information about breakpoints, refer to Debugger User's
      Guide.</p>
  </section>

  <funcs>
    <func>
      <name>i(AbsModule) -> {module,Module} | error</name>
      <name>i(AbsModules) -> ok</name>
      <name>ni(AbsModule) -> {module,Module} | error</name>
      <name>ni(AbsModules) -> ok</name>
      <fsummary>Interpret a module</fsummary>
      <type>
	<v>AbsModules = [AbsModule]</v>
	<v>AbsModule = Module | File | [Module | File]</v>
	<v>&nbsp;Module = atom()</v>
	<v>&nbsp;File = string()</v>
      </type>
      <desc>
	<p>Interprets the specified module(s). <c>i/1</c> interprets
	  the module only at the current node. <c>ni/1</c> interprets
	  the module at all known nodes.</p>

	<p>A module may be given by its module name (atom) or by its
	  file name. If given by its module name, the object code
	  <c>Module.beam</c> is searched for in the current path.
	  The source code <c>Module.erl</c> is searched for first in
	  the same directory as the object code, then in a <c>src</c>
	  directory next to it.</p>

	<p>If given by its file name, the file name may include a path
	  and the <c>.erl</c> extension may be omitted. The object code
	  <c>Module.beam</c> is searched for first in the same directory
	  as the source code, then in an <c>ebin</c> directory next to
	  it, and then in the current path.</p>

	<note>
	  <p>The interpreter needs both the source code and the object
	    code, and the object code <em>must</em> include debug
	    information. That is, only modules compiled with the option
	    <c>debug_info</c> set can be interpreted.</p>
	</note>

	<p>The functions returns <c>{module,Module}</c> if the module
	  was interpreted, or <c>error</c> if it was not.</p>

	<p>The argument may also be a list of modules/file names, in
	  which case the function tries to interpret each module as
	  specified above. The function then always returns <c>ok</c>,
	  but prints some information to stdout if a module could not be
	  interpreted.</p>
      </desc>
    </func>
	
    <func>
      <name>n(AbsModule) -> ok</name>
      <name>nn(AbsModule) -> ok</name>
      <fsummary>Stop interpreting a module</fsummary>
      <type>
	<v>AbsModule = Module | File | [Module | File]</v>
	<v>&nbsp;Module = atom()</v>
	<v>&nbsp;File = string()</v>
      </type>
      <desc>
	<p>Stops interpreting the specified module. <c>n/1</c> stops
	  interpreting the module only at the current node. <c>nn/1</c>
	  stops interpreting the module at all known nodes.</p>

	<p>As for <c>i/1</c> and <c>ni/1</c>, a module may be given by
	  either its module name or its file name.</p>
      </desc>
    </func>

    <func>
      <name>interpreted() -> [Module]</name>
      <fsummary>Get all interpreted modules</fsummary>
      <type>
	<v>Module = atom()</v>
      </type>
      <desc>
	<p>Returns a list with all interpreted modules.</p>
      </desc>
    </func>

    <func>
      <name>file(Module) -> File | {error,not_loaded}</name>
      <fsummary>Get the file name for an interpreted module</fsummary>
      <type>
	<v>Module = atom()</v>
	<v>File = string()</v>
      </type>
      <desc>
	<p>Returns the source code file name <c>File</c> for an
	  interpreted module <c>Module</c>.</p>
      </desc>
    </func>

    <func>
      <name>interpretable(AbsModule) -> true | {error,Reason}</name>
      <fsummary>Check if a module is possible to interpret</fsummary>
      <type>
	<v>AbsModule = Module | File</v>
	<v>&nbsp;Module = atom()</v>
	<v>&nbsp;File = string()</v>
	<v>Reason = no_src | no_beam | no_debug_info | badarg
	  | {app,App}</v>
	<v>&nbsp;App = atom()</v>
      </type>
      <desc>
	<p>Checks if a module is possible to interpret. The module can
	  be given by its module name <c>Module</c> or its source file
	  name <c>File</c>. If given by a module name, the module is
	  searched for in the code path.</p>

	<p>The function returns <c>true</c> if both source code and
	  object code for the module is found, the module has been
	  compiled with the option <c>debug_info</c> set and does not
	  belong to any of the applications Kernel, STDLIB, GS or
	  Debugger itself.</p>

	<p>The function returns <c>{error,Reason}</c> if the module for
	  some reason is not possible to interpret.</p>
	
	<p><c>Reason</c> is <c>no_src</c> if no source code is found or
	  <c>no_beam</c> if no object code is found. It is assumed that
	  the source- and object code are located either in the same
	  directory, or in <c>src</c> and <c>ebin</c> directories next
	  to each other.</p>

	<p><c>Reason</c> is <c>no_debug_info</c> if the module has not
	  been compiled with the option <c>debug_info</c> set.</p>

	<p><c>Reason</c> is <c>badarg</c> if <c>AbsModule</c> is not
	  found. This could be because the specified file does not
	  exist, or because <c>code:which/1</c> does not return a
	  beam file name, which is the case not only for non-existing
	  modules but also for modules which are preloaded or cover
	  compiled.</p>

	<p><c>Reason</c> is <c>{app,App}</c> where <c>App</c> is
	  <c>kernel</c>, <c>stdlib</c>, <c>gs</c> or <c>debugger</c> if
	  <c>AbsModule</c> belongs to one of these applications.</p>

	<p>Note that the function can return <c>true</c> for a module
	  which in fact is not interpretable in the case where
	  the module is marked as sticky or resides in a directory
	  marked as sticky, as this is not discovered until
	  the interpreter actually tries to load the module.</p>
      </desc>
    </func>

    <func>
      <name>auto_attach() -> false | {Flags,Function}</name>
      <name>auto_attach(false)</name>
      <name>auto_attach(Flags, Function)</name>
      <fsummary>Get/set when and how to attach to a process</fsummary>
      <type>
	<v>Flags = [init | break | exit]</v>
	<v>Function = {Module,Name,Args}</v>
	<v>&nbsp;Module = Name = atom()</v>
	<v>&nbsp;Args = [term()]</v>
      </type>
      <desc>
	<p>Gets and sets when and how to automatically attach to a
	  process executing code in interpreted modules. <c>false</c>
	  means never automatically attach, this is the default.
	  Otherwise automatic attach is defined by a list of flags and
	  a function. The following flags may be specified:</p>
	<list>
	  <item><c>init</c> - attach when a process for the very first
	    time calls an interpreted function.</item>
	  <item><c>break</c> - attach whenever a process reaches a
	    breakpoint.</item>
	  <item><c>exit</c> - attach when a process terminates.</item>
	</list>

	<p>When the specified event occurs, the function <c>Function</c>
	  will be called as:</p>
	<pre>
spawn(Module, Name, [Pid | Args])
	</pre>
	<p><c>Pid</c> is the pid of the process executing interpreted
	  code.</p>
      </desc>
    </func>

    <func>
      <name>stack_trace() -> Flag</name>
      <name>stack_trace(Flag)</name>
      <fsummary>Get/set if and how to save call frames</fsummary>
      <type>
	<v>Flag = all | no_tail | false</v>
      </type>
      <desc>
	<p>Gets and sets how to save call frames in the stack. Saving
	  call frames makes it possible to inspect the call chain of a
	  process, and is also used to emulate the stack trace if an
	  error (an exception of class error) occurs.</p>
	<list>
	  <item><c>all</c> - save information about all current calls,
	    that is, function calls that have not yet returned a value.
	    This is the default.</item>
	  <item><c>no_tail</c> - save information about current calls,
	    but discard previous information when a tail recursive call
	    is made. This option consumes less memory and may be
	    necessary to use for processes with long lifetimes and many
	    tail recursive calls.</item>
	  <item><c>false</c> - do not save any information about current
	    calls.</item>
	</list>
      </desc>
    </func>

    <func>
      <name>break(Module, Line) -> ok | {error,break_exists}</name>
      <fsummary>Create a breakpoint</fsummary>
      <type>
	<v>Module = atom()</v>
	<v>Line = int()</v>
      </type>
      <desc>
	<p>Creates a breakpoint at <c>Line</c> in <c>Module</c>.</p>
      </desc>
    </func>

    <func>
      <name>delete_break(Module, Line) -> ok</name>
      <fsummary>Delete a breakpoint</fsummary>
      <type>
	<v>Module = atom()</v>
	<v>Line = int()</v>
      </type>
      <desc>
	<p>Deletes the breakpoint located at <c>Line</c> in
	  <c>Module</c>.</p>
      </desc>
    </func>

    <func>
      <name>break_in(Module, Name, Arity) -> ok
	| {error,function_not_found}</name>
      <fsummary>Create breakpoints in the specified function</fsummary>
      <type>
	<v>Module = Name = atom()</v>
	<v>Arity = int()</v>
      </type>
      <desc>
	<p>Creates a breakpoint at the first line of every clause of 
	  the <c>Module:Name/Arity</c> function.</p>
      </desc>
    </func>

    <func>
      <name>del_break_in(Module, Name, Arity) -> ok
	| {error,function_not_found}</name>
      <fsummary>Delete breakpoints from the specified function
      </fsummary>
      <type>
	<v>Module = Name = atom()</v>
	<v>Arity = int()</v>
      </type>
      <desc>
	<p>Deletes the breakpoints at the first line of every clause of 
	  the <c>Module:Name/Arity</c> function.
	</p>
      </desc>
    </func>

    <func>
      <name>no_break() -> ok</name>
      <name>no_break(Module) -> ok</name>
      <fsummary>Delete all breakpoints</fsummary>
      <desc>
	<p>Deletes all breakpoints, or all breakpoints in <c>Module</c>.
	</p>
      </desc>
    </func>

    <func>
      <name>disable_break(Module, Line) -> ok</name>
      <fsummary>Make a breakpoint inactive</fsummary>
      <type>
	<v>Module = atom()</v>
	<v>Line = int()</v>
      </type>
      <desc>
	<p>Makes the breakpoint at <c>Line</c> in <c>Module</c>
	  inactive.</p>
      </desc>
    </func>

    <func>
      <name>enable_break(Module, Line) -> ok</name>
      <fsummary>Make a breakpoint active</fsummary>
      <type>
	<v>Module = atom()</v>
	<v>Line = int()</v>
      </type>
      <desc>
	<p>Makes the breakpoint at <c>Line</c> in <c>Module</c> active.
	</p>
      </desc>
    </func>

    <func>
      <name>action_at_break(Module, Line, Action) -> ok</name>
      <fsummary>Set the trigger action of a breakpoint</fsummary>
      <type>
	<v>Module = atom()</v>
	<v>Line = int()</v>
	<v>Action = enable | disable | delete</v>
      </type>
      <desc>
	<p>Sets the trigger action of the breakpoint at <c>Line</c> in
	  <c>Module</c> to <c>Action</c>.</p>
      </desc>
    </func>

    <func>
      <name>test_at_break(Module, Line, Function) -> ok</name>
      <fsummary>Set the conditional test of a breakpoint</fsummary>
      <type>
	<v>Module = atom()</v>
	<v>Line = int()</v>
	<v>Function = {Module,Name}</v>
	<v>&nbsp;Name = atom()</v>
      </type>
      <desc>
	<p>Sets the conditional test of the breakpoint at <c>Line</c> in
	  <c>Module</c> to <c>Function</c>. The function must
	  fulfill the requirements specified in the section
	  <em>Breakpoints</em> above.</p>
      </desc>
    </func>

    <func>
      <name>get_binding(Var, Bindings) -> {value,Value} | unbound</name>
      <fsummary>Retrieve a variable binding</fsummary>
      <type>
	<v>Var = atom()</v>
	<v>Bindings = term()</v>
	<v>Value = term()</v>
      </type>
      <desc>
	<p>Retrieves the binding of <c>Var</c>. This function is
	  intended to be used by the conditional function of a
	  breakpoint.</p>
      </desc>
    </func>

    <func>
      <name>all_breaks() -> [Break]</name>
      <name>all_breaks(Module) -> [Break]</name>
      <fsummary>Get all breakpoints</fsummary>
      <type>
	<v>Break = {Point,Options}</v>
	<v>&nbsp;Point = {Module,Line}</v>
	<v>&nbsp;&nbsp;Module = atom()</v>
	<v>&nbsp;&nbsp;Line = int()</v>
	<v>&nbsp;Options = [Status,Trigger,null,Cond|]</v>
	<v>&nbsp;&nbsp;Status = active | inactive</v>
	<v>&nbsp;&nbsp;Trigger = enable | disable | delete</v>
	<v>&nbsp;&nbsp;Cond = null | Function</v>
	<v>&nbsp;&nbsp;&nbsp;Function = {Module,Name}</v>
	<v>&nbsp;&nbsp;&nbsp;&nbsp;Name = atom()</v>
      </type>
      <desc>
	<p>Gets all breakpoints, or all breakpoints in <c>Module</c>.
	</p>
      </desc>
    </func>

    <func>
      <name>snapshot() -> [Snapshot]</name>
      <fsummary>Get information about all processes executing interpreted
	code</fsummary>
      <type>
	<v>Snapshot = {Pid, Function, Status, Info}</v>
	<v>&nbsp;Pid = pid()</v>
	<v>&nbsp;Function = {Module,Name,Args}</v>
	<v>&nbsp;&nbsp;Module = Name = atom()</v>
	<v>&nbsp;&nbsp;Args = [term()]</v>
	<v>&nbsp;Status = idle | running | waiting | break | exit
	  | no_conn</v>
	<v>&nbsp;Info = {} | {Module,Line} | ExitReason</v>
	<v>&nbsp;&nbsp;Line = int()</v>
	<v>&nbsp;&nbsp;ExitReason = term()</v>
      </type>
      <desc>
	<p>Gets information about all processes executing interpreted code.
	</p>
	<list>
	  <item><c>Pid</c> - process identifier.</item>
	  <item><c>Function</c> - first interpreted function called by
	    the process.</item>
	  <item><c>Status</c> - current status of the process.</item>
	  <item><c>Info</c> - additional information.</item>
	</list>
	<p><c>Status</c> is one of:</p>
	<list>
	  <item><c>idle</c> - the process is no longer executing
	    interpreted code. <c>Info={}</c>.</item>
	  <item><c>running</c> - the process is running. <c>Info={}</c>.
	  </item>
	  <item><c>waiting</c> - the process is waiting at a
	    <c>receive</c>. <c>Info={}</c>.</item>
	  <item><c>break</c> - process execution has been stopped,
	    normally at a breakpoint. <c>Info={Module,Line}</c>.</item>
	  <item><c>exit</c> - the process has terminated.
	    <c>Info=ExitReason</c>.</item>
	  <item><c>no_conn</c> - the connection is down to the node
	    where the process is running. <c>Info={}</c>.</item>
	</list>
      </desc>
    </func>

    <func>
      <name>clear() -> ok</name>
      <fsummary>Clear information about processes executing interpreted
	code</fsummary>
      <desc>
	<p>Clears information about processes executing interpreted code
	  by removing all information about terminated processes.</p>
      </desc>
    </func>

    <func>
      <name>continue(Pid) -> ok | {error,not_interpreted}</name>
      <name>continue(X,Y,Z) -> ok | {error,not_interpreted}</name>
      <fsummary>Resume process execution</fsummary>
      <type>
	<v>Pid = pid()</v>
	<v>X = Y = Z = int()</v>
      </type>
      <desc>
	<p>Resume process execution for <c>Pid</c>, or for
	  <c>c:pid(X,Y,Z)</c>.</p>
      </desc>
    </func>
  </funcs>
</erlref>


