# Creator-Defined Statements

Creator-Defined Statements (CDS) allow you to add your own statements to Ren'Py. This makes it possible to add things that are not supported by the current syntax of Ren'Py. CDS are more flexible than the direct Python code. Most often, CDS are used when you have a repeatable construction. For example, calling a function with one argument. Ren'Py does not know what this function does and how it should be executed, so Ren'Py does not do anything with it until execution and has an error if an exception occurs. Using the CDS allows you to check the correctness of the syntax using parse (for example, check that the argument is a valid string), to ignore incorrect data at execution (for non-critical functions, it is better to skip the execute than to throw an exception), predict displayables (if the function uses them), and give you addition information during lint (if at runtime it was ignored you can have a report here). The CDS does not guarantee that the execution will be successful, but the better you code your statement, the better Ren'Py can "understand" what you expect from it.

Creator-defined statements must be defined in a `python early` block. What's more, the filename containing the user-defined statement must be be loaded earlier than any file that uses it. Since Ren'Py loads files in Unicode sort order, it generally makes sense to prefix the name of any file containing a user-defined statement with 01, or some other small number.

A creator-defined statement cannot be used in the file in which it is defined.

Creator-defined statement are registered using the `renpy.register_statement()` function.

`renpy.``register_statement`(name, parse=None, lint=None, execute=None, predict=None, next=None, scry=None, block=False, init=False, translatable=False, execute_init=None, init_priority=0, label=None, warp=None, translation_strings=None, force_begin_rollback=False)

  This registers a user-defined statement.

  name
    This is either a space-separated list of names that begin the statement, or the empty string to define a new default statement (the default statement will replace the say statement).
  block
    When this is False, the statement does not expect a block. When True, it expects a block, but leaves it up to the lexer to parse that block. If the string "script", the block is interpreted as containing one or more Ren'Py script language statements. If the string "possible", the block expect condition is determined by the parse function.
  parse
    This is a function that takes a Lexer object. This function should parse the statement, and return an object. This object is passed as an argument to all the other functions. The lexer argument has the following methods:
  lint
    This is called to check the statement. It is passed a single argument, the object returned from parse. It should call renpy.error to report errors.
  execute
    This is a function that is called when the statement executes. It is passed a single argument, the object returned from parse.
  execute_init
    This is a function that is called at init time, at priority 0.
  predict
    This is a function that is called to predict the images used by the statement. It is passed a single argument, the object returned from parse. It should return a list of displayables used by the statement.
  next

    This is a function that is called to determine the next statement.

    If block is not "script", this is passed a single argument, the object returned from the parse function. If block is "script", an additional argument is passed, an object that names the first statement in the block.

    The function should return either a string giving a label to jump to, the second argument to transfer control into the block, or None to continue to the statement after this one.

  label
    This is a function that is called to determine the label of this statement. If it returns a string, that string is used as the statement label, which can be called and jumped to like any other label.
  warp
    This is a function that is called to determine if this statement should execute during warping. If the function exists and returns true, it's run during warp, otherwise the statement is not run during warp.
  scry
    Used internally by Ren'Py.
  init
    True if this statement should be run at init-time. (If the statement is not already inside an init block, it's automatically placed inside an init block.) This calls the execute function, in addition to the execute_init function.
  init_priority
    An integer that determines the priority of initialization of the init block.
  translation_strings
    A function that is called with the parsed block. It's expected to return a list of strings, which are then reported as being available to be translated.
  force_begin_rollback
    This should be set to true on statements that are likely to cause the end of a fast skip, similar to `menu` or `call screen`.

The parse method takes a Lexer object:

class `Lexer`
  `error`(msg)

    Adds a msg (with the current position) in the list of detected parsing errors. This interrupts the parsing of the current statement, but does not prevent further parsing.

  `require`(thing, name=None)

    Tries to parse thing, and reports an error if it cannot be done.

    If thing is a string, tries to parse it using `match()`. Otherwise, thing must be a other method on this lexer object, which is called without arguments. If name is not specified, the name of the method will be used in the message (or thing if it's a string), otherwise the name will be used.

  `eol`()

    True if the lexer is at the end of the line.

  `expect_eol`()

    If we are not at the end of the line, raise an error.

  `expect_noblock`(stmt)

    Called to indicate this statement does not expect a block. If a block is found, raises an error. stmt should be a string, it will be added to the message with an error.

  `expect_block`(stmt)

    Called to indicate that the statement requires that a non-empty block is present. stmt should be a string, it will be added to the message with an error.

  `match`(re)

    Matches an arbitrary regexp string.

    All of the statements in the lexer that match things are implemented in terms of this function. They first skip whitespace, then attempt to match against the line. If the match succeeds, the matched text is returned. Otherwise, None is returned, and the state of the lexer is unchanged.

  `keyword`(s)

    Matches s as a keyword.

  `name`()

    Matches a name. This does not match built-in keywords.

  `word`()

    Matches any word, including keywords. Returns the text of the matched word.

  `image_name_component`()

    Matches an image name component. Unlike a word, a image name component can begin with a number.

  `string`()

    Matches a Ren'Py string.

  `integer`()

    Matches an integer, returns a string containing the integer.

  `float`()

    Matches a floating point number, returns a string containing the floating point number.

  `label_name`(declare=False)

    Matches a label name, either absolute or relative. If declare is true, then the global label name is set. (Note that this does not actually declare the label - the statement is required to do that by returning it from the label function.)

  `simple_expression`()

    Matches a simple Python expression, returns it as a string. This is often used when you expect a variable name. It is not recommended to change the result. The correct action is to evaluate the result in the future.

  `delimited_python`(delim)

    Matches a Python expression that ends in a delim, for example ':'. This is often used when you expect a condition until the delimiter. It is not recommended to change the result. The correct action is to evaluate the result in the future. This raises an error if end of line is reached before the delimiter.

  `arguments`()

    This must be called before the parentheses with the arguments list, if they are not specified returns None, otherwise returns an object representing the arguments to a function call. This object has an `evaluate` method on it that takes an optional scope dictionary, and returns a tuple in which the first component is a tuple of positional arguments, and the second component is a dictionary of keyword arguments.

  `rest`()

    Skips whitespace, then returns the rest of the line.

  `checkpoint`()

    Returns an opaque object representing the current state of the lexer.

  `revert`(o)

    When o is the object returned from checkpoint(), reverts the state of the lexer to what it was when checkpoint() was called. (This is used for backtracking.)

  `subblock_lexer`()

    Return a Lexer for the block associated with the current line.

  `advance`()

    In a subblock lexer, advances to the next line. This must be called before the first line, so the first line can be parsed. Returns True if we've successfully advanced to a line in the block, or False if we have advanced beyond all lines in the block.

## Lint Utility Functions

These functions are useful in writing lint functions.

`renpy.``check_text_tags`(s)

  Checks the text tags in s for correctness. Returns an error string if there is an error, or None if there is no error.

`renpy.``error`(msg)

  Reports msg, a string, as as error for the user. This is logged as a parse or lint error when approprate, and otherwise it is raised as an exception.

`renpy.``try_compile`(where, expr, additional=None)

  Tries to compile an expression, and writes an error to lint.txt if it fails.

  where
    A string giving the location the expression is found. Used to generate an error message of the form "Could not evaluate expr in where."
  expr
    The expression to try compiling.
  additional
    If given, an additional line of information that is addded to the error message.

`renpy.``try_eval`(where, expr, additional=None)

  Tries to evaluate an expression, and writes an error to lint.txt if it fails.

  where
    A string giving the location the expression is found. Used to generate an error message of the form "Could not evaluate expr in where."
  expr
    The expression to try evaluating.
  additional
    If given, an additional line of information that is addded to the error message.

## Example

This creates a new statement `line` that allows lines of text to be specified without quotes.

    python early:

        def parse_smartline(lex):
            who = lex.simple_expression()
            what = lex.rest()
            return (who, what)

        def execute_smartline(o):
            who, what = o
            renpy.say(eval(who), what)

        def lint_smartline(o):
            who, what = o
            try:
                eval(who)
            except:
                renpy.error("Character not defined: %s" % who)

            tte = renpy.check_text_tags(what)
            if tte:
                renpy.error(tte)

        renpy.register_statement("line", parse=parse_smartline, execute=execute_smartline, lint=lint_smartline)

This can be used by writing:

    line e "These quotes will show up," Eileen said, "and don't need to be backslashed."