# phpman > perldoc > HTML::Mason::Compiler

## NAME
    [HTML::Mason::Compiler](https://www.chedong.com/phpMan.php/perldoc/HTML%3A%3AMason%3A%3ACompiler/markdown) - Compile Mason component source

## SYNOPSIS
      package [My::Funky::Compiler](https://www.chedong.com/phpMan.php/perldoc/My%3A%3AFunky%3A%3ACompiler/markdown);

      use base qw([HTML::Mason::Compiler](https://www.chedong.com/phpMan.php/perldoc/HTML%3A%3AMason%3A%3ACompiler/markdown));

## DESCRIPTION
    The compiler starts the compilation process by calling its lexer's "lex" method and passing
    itself as the "compiler" parameter. The lexer then calls various methods in the compiler as it
    parses the component source.

PARAMETERS TO THE new() CONSTRUCTOR
    allow_globals
        List of variable names, complete with prefix ("$@%"), that you intend to use as globals in
        components. Normally global variables are forbidden by "strict", but any variable mentioned
        in this list is granted a reprieve via a "use vars" statement. For example:

            allow_globals => [qw($DBH %session)]

        In a mod_perl environment, $r (the request object) is automatically added to this list.

    default_escape_flags
        Escape flags to apply to all <% %> expressions by default. The current valid flags are

            h - escape for HTML ('<' => '&lt;', etc.)
            u - escape for URL (':' => '%3A', etc.)

        The developer can override default escape flags on a per-expression basis; see the escaping
        expressions section of the developer's manual.

        If you want to set *multiple* flags as the default, this should be given as a reference to
        an array of flags.

    enable_autoflush
        True or false, default is true. Indicates whether components are compiled with support for
        autoflush. The component can be compiled to a more efficient form if it does not have to
        check for autoflush mode, so you should set this to 0 if you can.

    lexer
        The Lexer object to associate with this Compiler. By default a new object of class
        lexer_class will be created.

    lexer_class
        The class to use when creating a lexer. Defaults to [HTML::Mason::Lexer](https://www.chedong.com/phpMan.php/perldoc/HTML%3A%3AMason%3A%3ALexer/markdown).

    preprocess
        Sub reference that is called to preprocess each component before the compiler does it's
        magic. The sub is called with a single parameter, a scalar reference to the script. The sub
        is expected to process the script in-place. This is one way to extend the [HTML::Mason](https://www.chedong.com/phpMan.php/perldoc/HTML%3A%3AMason/markdown) syntax
        with new tags, etc., although a much more flexible way is to subclass the Lexer or Compiler
        class. See also postprocess_text and postprocess_perl.

    postprocess_text
        Sub reference that is called to postprocess the text portion of a compiled component, just
        before it is assembled into its final subroutine form. The sub is called with a single
        parameter, a scalar reference to the text portion of the component. The sub is expected to
        process the string in-place. See also preprocess and postprocess_perl.

    postprocess_perl
        Sub reference that is called to postprocess the Perl portion of a compiled component, just
        before it is assembled into its final subroutine form. The sub is called with a single
        parameter, a scalar reference to the Perl portion of the component. The sub is expected to
        process the string in-place. See also preprocess and postprocess_text.

    use_source_line_numbers
        True or false, default is true. Indicates whether component line numbers that appear in
        error messages, stack traces, etc. are in terms of the source file instead of the object
        file. Mason does this by inserting '#line' directives into compiled components. While source
        line numbers are more immediately helpful, object file line numbers may be more appropriate
        for in-depth debugging sessions.

## ACCESSOR METHODS
    All of the above properties have read-only accessor methods of the same name.

    You cannot change any property of a compiler after it has been created - among other things,
    this would potentially invalidate any existing cached component objects or object files. Your
    best bet is to create different compiler objects and load them into different interpreters.

## METHODS
    There are several methods besides the compilation callbacks below that a Compiler subclass needs
    to implement.

### compile
        This method has several parameters:

        *       comp_source (required)

                Either a scalar or reference to a scalar containing the component source.

        *       name (required)

                The name of the component. This should be the filename of the component if it is
                file-based, or some other clear identifier of the component source.

        *       comp_path (required)

                This should be the component's path.

        *       fh (optional)

                If this is given then the output of the compiler will be sent directly to this
                handle, rather than being buffered in memory. This is an optimization to avoid
                memory usage.

    object_id
        This method should return a unique id for the given compiler object. This is used by the
        interpreter when determining the object directory, for example.

### Compilation Callbacks
    These are methods called by the Lexer while processing a component source. You may wish to
    override some of these methods if you're implementing your own custom Compiler class.

### start_component
        This method is called by the Lexer when it starts processing a component.

### end_component
        This method is called by the Lexer when it finishes processing a component.

### start_block
        This method is called by the Lexer when it encounters an opening Mason block tag like
        "<%perl>" or "<%args>". Its main purpose is to keep track of the nesting of different kinds
        of blocks within each other. The type of block ("init", "once", etc.) is passed via the
        "block_type" parameter.

### end_block
        This method is called by the Lexer when it encounters a closing Mason block tag like
        "</%perl>" or "</%args>". Like "start_block()", its main purpose is to help maintain
        syntactic integrity.

    *_block(block => <string>, [ block_type => <string> ])
        Several compiler methods like "doc_block()", "text_block()", and "raw_block()" are called by
        the Lexer after "start_block()" when it encounters blocks of certain types. These methods
        actually do the work of putting the body of a block into the compiled data structure.

        The methods that follow this pattern are "init_block()", "perl_block()", "doc_block()",
        "text_block()", and "raw_block()". The last method is called for all "<%once>",
        "<%cleanup>", "<%filter>", "<%init>", "<%perl>", and "<%shared>" blocks.

### text
        Inserts the text contained in a "text" parameter into the component for verbatim output.

        This is called when the lexer finds plain text in a component.

### variable_declaration
        Inserts a variable declaration from the "<%args>" section into the component.

        The type will be either "$", "@", or "%", indicating a scalar, array, or hash. The name is
        the variable name without the leading sigil. The default is everything found after the first
        "=>" on an "<%args>" block line, and may include a comment.

### key_value_pair
        Inserts a key-value pair from a "<%flags>" or "<%attr>" section into the component.

        The "block_type" parameter will be either "flags" or "attr".

### start_named_block
        Analogous to item_start_block, but starts a "named" block ("<%method>" or "<%def>").

### end_named_block
        Called by the Lexer to end a "named" block.

### substitution
        Called by the Lexer when it encounters a substitution tag ("<% ... %>").

        The value of the "escape" parameter will be everything found after the pipe (|) in the
        substitution tag, and may be more than one character such as "nh".

### component_call
        Called by the Lexer when it encounters a component call tag without embedded content ("<&
        ... &>").

        The "call" parameter contains the entire contents of the tag.

### component_content_call
        Called by the Lexer when it encounters a component call tag with embedded content ("<&| ...
        &>").

### component_content_call_end
        Called by the Lexer when it encounters an ending tag for a component call with content
        ("</&>"). Note that there is no corresponding "component_call_end()" method for component
        calls without content, because these calls don't have ending tags.

### perl_line
        Called by the Lexer when it encounters a "%"-line.

## SUBCLASSING
    We recommend that any parameters you add to Compiler be read-only, because the compiler
    object_id is only computed once on creation and would not reflect any changes to Lexer
    parameters.