| SciTE Lua Scripting Extension

### Lua Scripting Extension Notes

The SciTE Lua Scripting Extension uses a verbatim copy of Lua 5.0.2 as its scripting engine. Currently, all of the standard libraries are included, although this list may be trimmed in a future revision.

Lua is Copyright (C) 2003 TeCGraf, PUC-Rio. The complete Lua license is included in `luaCOPYRIGHT` in the SciTE installation directory. To find more information about Lua, including documentation for the language itself, visit www.lua.org.

For more ideas about what Lua can do, you may also want to check out the community portal, lua-users.org.

#### SciTE Properties and Lua Event / Command Handlers

The properties ext.lua.startup.script and extension.filepattern can be used to define commands and event handlers that will be called by the SciTE. Other properties beginning with ext.lua may also influence how Lua behaves. See the SciTE Documentation for more details on this.

By defining functions in the startup script or the active extension script, you can tailor SciTE to your needs, adding new behavior and functionality that is tightly integrated.

To begin, you can handle any many of the events exposed by the SciTE Extension Interface. You do this simply by defining functions with the same name as the event. Currently, `OnOpen`, `OnSwitchFile`, `OnSave`, `OnBeforeSave`, `OnChar`, `OnSavePointReached`, `OnSavePointLeft`, `OnDoubleClick`, `OnMarginClick`, and `OnUserListSelection` are supported.

For some of these events, SciTE will pass one or more arguments to the event handler function: `OnOpen`, `OnSwitchFile`, `OnSave`, and `OnBeforeSave` will receive the filename of the affected buffer as their first argument. An `OnChar` handler should expect a single-character string argument. `OnUserListSelection` receives two arguments: a number indicating the list type, and a string indicating the selected item text. The other event handlers will not be passed any arguments.

Event handlers return a boolean value to indicate whether SciTE should continue processing the event. Return a true value to indicate that the event has been fully handled, and that no further handlers should be called. Return a false value to give other extensions a chance to process the same event. In many but not all cases, a well behaved event handler will return false. Remember that, in Lua, the only non-true values are `false` and `nil`. Unlike in C++, Python and many other languages, 0 evaluates to `true`.

There is one additional event handler, `OnClear`, that is not expressly defined in the Extension interface, but is exposed to Lua. Whenever SciTE re-reads the properties (which occurs every time you switch buffers or open a new file, but can also occur at other times), the Lua Extension removes any globals that were created since the last time properties were read, and restores any globals that were overwritten. Then, if the startup script defines a function `OnClear`, that function will be called so that scripts have a chance to clean up other changes they might have made outside of the Lua global scope (e.g. dynamic properties modified through the props object; see below) and/or to tailor the Lua environment according to local properties for the current buffer.

After this, SciTE reads the properties and ultimately loads the extension script, if one is defined. However, at the time when the `OnClear` event fires, the extension script is not yet loaded. Thus, `OnClear` can only be defined in the startup script, not in an extension script.

In addition to event handlers, you can also use define new commands that are available through the Tools menu or through keyboard shortcuts. To specify that a command that will be handled by Lua, specify subsystem 3 for the command. Then, to implement the command using Lua, just define a global function. The command name is the function name.

You can also use predefined functions like `dofile` and `dostring` as tool commands.

Anything specified after the command name is passed to the Lua function as a single string argument. An example of a command, using the built-in dofile command, is shown below.

      command.name.1.*=Run My Script
      command.subsystem.1.*=3
      command.1.*=dofile $(SciteDefaultHome)/My Script.lua

Note that the command line is "not" evaluated directly as a Lua script.

If there is no function matching the command name, no error will be displayed. This is because Lua assumes in this case that the command is meant for some other extension, such as the SciTE Director Extension. However, if the command function is found, but fails to execute, an error is reported.

#### Predefined Lua Functions and Objects:

Within Lua scripts you can use the following functions / objects:

      trace(s) - writes s to the output pane (no prefix, no newlines)
      dostring(s) - executes s as a Lua string, like Lua 4's dostring
      editor - the editor pane
      output - the output pane
      props - a pseudo-table representing the SciTE properties
      buffer - a table associated with the current buffer or document
      scite - a namespace for functions which control SciTE.

In addition, all constants defined in Scintilla.iface are exposed as Lua globals variables. Function names are exposed as their block capital equivalents, with the SCI_ prefix.

All functions and objects defined in the Lua standard library are also available. Although dostring was deprecated in Lua 5, it is restored since some have said it would be useful in tool commands.

A function `_ALERT()` is also defined to be an alias for the built-in `print()`, which prints the alert message (plus a newline) to the window. This provides a reasonable way for Lua to present error messages to the user. You are free to override `_ALERT` with a different definition if you prefer.

The props pseudo-table allows you to read or write properties by name using normal Lua table-access semantics, e.g. `props["property.name"]`. As with Lua tables, you can also un-set a property by assigning nil to its key.

When you assign a value to a property from Lua, this overrides any values specified in the configuration files for that setting. The underlying file properties are not changed. If you later assign nil to the same property from Lua, this removes the run-time setting, allowing any file-based property setting to show through once again.

The editor and output panes support the following properties and methods:

      textrange(startPos, endPos) - gets the text in the specified range

      findtext(text, [flags], [startPos, [endPos]])
        - returns the start and end of the first match, or nil if no match
        - flags can be 0 (the default), or a combination of SCFIND constants
          such as SCFIND_WHOLEWORD, SCFIND_MATCHCASE, and SCFIND_REGEXP

      match(text, [flags], [startPos])
        - returns a generator that allows you to loop over the matches
          i.e. for m in editor:match(text, flags) do ... end
        - the match object (i.e. the loop counter m in the above
          example) supports read-only properties pos, len, and text;
          and also supports a function replace(replaceText) to
          support search and replace.
        - while looping through matches, if the document is modified
          by any method other than the loop counter's replace method,
          this may cause the match generator to lose its place.
        - also, do not attempt to store the match object for later
          access outside the loop; it will not be useable.

      append(text) - appends text to the end of the document
      insert(pos, text) - inserts text at the specified position
      remove(startPos, endPos) - removes the text in the range

Most of the functions defined in Scintilla.iface are also be exposed as pane methods. Those functions having simple parameters (string, boolean, and numeric types) are fully supported. For example, `editor:InsertText(pos, text)` does practically the same thing as `editor:insert(pos, text)`. Functions having a stringresult parameter will include a string in the return value. For both strings and stringresults, if the function is documented as expecting a length as its first parameter, you do not pass the length from Lua. Instead, it is inferred from the context.

The keymod parameter type has partial support. When an iface function is declared as taking a keymod, the Lua equivalent expects two numbers: first the key code (e.g. `SCK_LEFT` or `string.byte("'")`, and second the modifiers (e.g. `SCMOD_CTRL`).

Functions that have more complex parameters are not supported.

Functions that are declared to return a numeric type have the result added to their return value. If the function also has a stringresult, that comes first, followed by the numeric return value.

Some functions are declared as 'get' or 'set' rather than 'fun' in the iface file. These are generally exposed to Lua as properties, e.g. `editor.TabSize = 8`. Some of the getters and setters also have a parameter. Where possible, these are exposed to Lua as indexed properties, e.g. `editor.StyleBold[SCE_PROPS_DEFAULT] = true`. However, if an iface function is declared as get / set but cannot be mapped to a Lua property, it is exposed as a Lua function instead.

It is intended that a complete guide to the iface functions and properties should be added to the documentation, so you don't have to look at the iface file and do the mental text manipulation. This is not done yet, but would be a good project for someone. ScintillaDoc would be a good template to follow. An api file would also be a good addition.

The `scite` namespace includes the following functions:

      scite.Open(filename)
        - opens a file in a new buffer
        - activates the file's buffer if it is already opened.

      scite.SendEditor(SCI_constant, ...)
        - sends a message to the editor pane
        - equivalent to the corresponding iface function or property

      scite.SendOutput(SCI_constant, ...)
        - sends a message to the output pane

      scite.ConstantName(number)
        - returns the symbolic name of a Scintilla / SciTE constant

`Open` requires special care. When the buffer changes in SciTE, the Lua global namespace is reset to its initial state, and any extension script associated with the new buffer is loaded. Thus, when you call Open, this may change the environment in which your current script is running. When possible, you can avoid confusion by simply returning after scite.Open, but when that is not possible, just bear in mind that there are side effects. Local variables, unlike globals, will be retained after the buffer change until your script returns.

The `SendEditor` and `SendOuput` functions duplicate the functionality of the editor and output objects, providing access to these through an interface that is more familiar to Scintilla C++ developers. This may be useful for prototyping C++ code using Lua. Internally, `SendEditor` and `SendOutput` are translated to the corresponding iface function or property, so their arguments and return types are identical. (Although the calling convention for properties is obviously different.)

The ConstantName function may be useful when generating debug messages, or if extending the SciTE LuaExtension to support macro recording.

#### Disabling Lua

Lua is currently loaded just-in-time, before it is first used. The ways that Lua can become are through the ext.lua.startup.script property, by naming a lua file named in the extension.filepattern property, or by using the extension mechanism to define tool commands (i.e. subsystem 3). If you do not do any of these things, the Lua scripting engine is not loaded, and for all practical purposes, SciTE should behave as it did before Lua was added.

Nevertheless, it is still possible to build SciTE without the Lua support. To do this, simply define the variable `NO_LUA` when you build it, e.g. for MSVC, `nmake -f scite.mak -DNO_LUA`; or with GNU tools, `make NO_LUA=1`.