# int

### MODULE

int

### MODULE SUMMARY

Interpreter Interface

### DESCRIPTION

The Erlang interpreter provides mechanisms for breakpoints and stepwise execution of code. It is mainly intended to be used by the Debugger, see Debugger User's Guide and `debugger(3)`.

From the shell, it is possible to:

- Specify which modules should be interpreted.
- Specify breakpoints.
- Monitor the current status of all processes executing code in interpreted modules, also processes at other Erlang nodes.

By attaching to 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 `int.erl` for available functions and `dbg_ui_trace.erl` for possible messages.

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.

### Breakpoints

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.

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

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

### EXPORTS

`i(AbsModule) -> {module,Module} | error`
`i(AbsModules) -> ok`
`ni(AbsModule) -> {module,Module} | error`
`ni(AbsModules) -> ok`

Types:

`AbsModules = [AbsModule]`
`AbsModule = Module | File | [Module | File]`
`Module = atom()`
`File = string()`

Interprets the specified module(s). `i/1` interprets the module only at the current node. `ni/1` interprets the module at all known nodes.

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

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

| The interpreter needs both the source code and the object code, and the object code must include debug information. That is, only modules compiled with the option `debug_info` set can be interpreted.

The functions returns `{module,Module}` if the module was interpreted, or `error` if it was not.

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 `ok`, but prints some information to stdout if a module could not be interpreted.

`n(AbsModule) -> ok`
`nn(AbsModule) -> ok`

Types:

`AbsModule = Module | File | [Module | File]`
`Module = atom()`
`File = string()`

Stops interpreting the specified module. `n/1` stops interpreting the module only at the current node. `nn/1` stops interpreting the module at all known nodes.

As for `i/1` and `ni/1`, a module may be given by either its module name or its file name.

`interpreted() -> [Module]`

Types:

`Module = atom()`

Returns a list with all interpreted modules.

`file(Module) -> File | {error,not_loaded}`

Types:

`Module = atom()`
`File = string()`

Returns the source code file name `File` for an interpreted module `Module`.

`interpretable(AbsModule) -> true | {error,Reason}`

Types:

`AbsModule = Module | File`
`Module = atom()`
`File = string()`
`Reason = no_src | no_beam | no_debug_info | badarg | {app,App}`
`App = atom()`

Checks if a module is possible to interpret. The module can be given by its module name `Module` or its source file name `File`. If given by a module name, the module is searched for in the code path.

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

The function returns `{error,Reason}` if the module for some reason is not possible to interpret.

`Reason` is `no_src` if no source code is found or `no_beam` if no object code is found. It is assumed that the source- and object code are located either in the same directory, or in `src` and `ebin` directories next to each other.

`Reason` is `no_debug_info` if the module has not been compiled with the option `debug_info` set.

`Reason` is `badarg` if `AbsModule` is not found. This could be because the specified file does not exist, or because `code:which/1` 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.

`Reason` is `{app,App}` where `App` is `kernel`, `stdlib`, `gs` or `debugger` if `AbsModule` belongs to one of these applications.

Note that the function can return `true` 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.

`auto_attach() -> false | {Flags,Function}`
`auto_attach(false)`
`auto_attach(Flags, Function)`

Types:

`Flags = [init | break | exit]`
`Function = {Module,Name,Args}`
`Module = Name = atom()`
`Args = [term()]`

Gets and sets when and how to automatically attach to a process executing code in interpreted modules. `false` 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:

- `init` - attach when a process for the very first time calls an interpreted function.
- `break` - attach whenever a process reaches a breakpoint.
- `exit` - attach when a process terminates.

When the specified event occurs, the function `Function` will be called as:

    spawn(Module, Name, [Pid | Args])

`Pid` is the pid of the process executing interpreted code.

`stack_trace() -> Flag`
`stack_trace(Flag)`

Types:

`Flag = all | no_tail | false`

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.

- `all` - save information about all current calls, that is, function calls that have not yet returned a value. This is the default.
- `no_tail` - 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.
- `false` - do not save any information about current calls.

`break(Module, Line) -> ok | {error,break_exists}`

Types:

`Module = atom()`
`Line = int()`

Creates a breakpoint at `Line` in `Module`.

`delete_break(Module, Line) -> ok`

Types:

`Module = atom()`
`Line = int()`

Deletes the breakpoint located at `Line` in `Module`.

`break_in(Module, Name, Arity) -> ok | {error,function_not_found}`

Types:

`Module = Name = atom()`
`Arity = int()`

Creates a breakpoint at the first line of every clause of the `Module:Name/Arity` function.

`del_break_in(Module, Name, Arity) -> ok | {error,function_not_found}`

Types:

`Module = Name = atom()`
`Arity = int()`

Deletes the breakpoints at the first line of every clause of the `Module:Name/Arity` function.

`no_break() -> ok`
`no_break(Module) -> ok`

Deletes all breakpoints, or all breakpoints in `Module`.

`disable_break(Module, Line) -> ok`

Types:

`Module = atom()`
`Line = int()`

Makes the breakpoint at `Line` in `Module` inactive.

`enable_break(Module, Line) -> ok`

Types:

`Module = atom()`
`Line = int()`

Makes the breakpoint at `Line` in `Module` active.

`action_at_break(Module, Line, Action) -> ok`

Types:

`Module = atom()`
`Line = int()`
`Action = enable | disable | delete`

Sets the trigger action of the breakpoint at `Line` in `Module` to `Action`.

`test_at_break(Module, Line, Function) -> ok`

Types:

`Module = atom()`
`Line = int()`
`Function = {Module,Name}`
`Name = atom()`

Sets the conditional test of the breakpoint at `Line` in `Module` to `Function`. The function must fulfill the requirements specified in the section Breakpoints above.

`get_binding(Var, Bindings) -> {value,Value} | unbound`

Types:

`Var = atom()`
`Bindings = term()`
`Value = term()`

Retrieves the binding of `Var`. This function is intended to be used by the conditional function of a breakpoint.

`all_breaks() -> [Break]`
`all_breaks(Module) -> [Break]`

Types:

`Break = {Point,Options}`
`Point = {Module,Line}`
`Module = atom()`
`Line = int()`
`Options = [Status,Trigger,null,Cond|]`
`Status = active | inactive`
`Trigger = enable | disable | delete`
`Cond = null | Function`
`Function = {Module,Name}`
`Name = atom()`

Gets all breakpoints, or all breakpoints in `Module`.

`snapshot() -> [Snapshot]`

Types:

`Snapshot = {Pid, Function, Status, Info}`
`Pid = pid()`
`Function = {Module,Name,Args}`
`Module = Name = atom()`
`Args = [term()]`
`Status = idle | running | waiting | break | exit | no_conn`
`Info = {} | {Module,Line} | ExitReason`
`Line = int()`
`ExitReason = term()`

Gets information about all processes executing interpreted code.

- `Pid` - process identifier.
- `Function` - first interpreted function called by the process.
- `Status` - current status of the process.
- `Info` - additional information.

`Status` is one of:

- `idle` - the process is no longer executing interpreted code. `Info={}`.
- `running` - the process is running. `Info={}`.
- `waiting` - the process is waiting at a `receive`. `Info={}`.
- `break` - process execution has been stopped, normally at a breakpoint. `Info={Module,Line}`.
- `exit` - the process has terminated. `Info=ExitReason`.
- `no_conn` - the connection is down to the node where the process is running. `Info={}`.

`clear() -> ok`

Clears information about processes executing interpreted code by removing all information about terminated processes.

`continue(Pid) -> ok | {error,not_interpreted}`
`continue(X,Y,Z) -> ok | {error,not_interpreted}`

Types:

`Pid = pid()`
`X = Y = Z = int()`

Resume process execution for `Pid`, or for `c:pid(X,Y,Z)`.

### AUTHORS

Gunilla Arendt - support@erlang.ericsson.se

debugger 3.1
Copyright © 1991-2006 Ericsson AB