# 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.

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.

  `has_block`()

    True if the current line has a non-empty block.

  `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.

  `renpy_statement`()

    When called, this parses the current line as a Ren’Py script statement, generating an error if this is not possible. This method returns an opaque object that can be returned from get_next() or passed to `renpy.jump()` or `renpy.call()`. This object should not be stored except as part of the parse result of the statement.

    When the statement returned from this completes, control is transfered to the statement after the creator-defined statement. (Which might be the statement created using post_execute).

  `renpy_block`(empty=False)

    This parses all of the remaining lines in the current block as Ren’Py script, and returns a SubParse corresponding to the first statement in the block. The block is chained together such that all statements in the block are run, and then control is transferred to the statement after this creator-defined statement.

    Note that this parses the current block. In the more likely case that you’d like to parse the subblock of the current statement, the correct way to do that is:

        def mystatement_parse(l):

            l.require(':')
            l.expect_eol()
            l.expect_block("mystatement")

            child = l.subblock_lexer().renpy_block()

            return { "child" : child }

    empty

      If True, allows an empty block to be parsed. (An empty block is equivalent to a block with a single `pass` statement.)

      If False, an empty block triggers an error.

  `catch_error`()

    This is a context decorator, used in conjunction with the with statement, that catches and reports lexer errors inside its context block, then continues after the block.

    Here’s an example of how it can be used to report multiple errors in a single subblock.

        def mystatement_parse(l):

            l.require(':')
            l.expect_eol()
            l.expect_block("mystatement")

            strings = [ ]
            ll = l.subblock_lexer()

            while ll.advance():
                with ll.catch_errors():
                    strings.append(ll.require(ll.string))
                    ll.expect_noblock("string inside mystatement")
                    ll.expect_eol()

            return { "strings" : strings }

## Lint Utility Functions

These functions are useful in writing lint functions.

## 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."