Organization

| Organization |

The framework is highly modular and is organized in layers:

iterator | actor
debug
attribute | dynamic | error_handling | symbols | tree | utility
meta
core
scanner | primitives | composite | non_terminal

Spirit has four layers, plus an independent top layer. The independent layer, comprising of actor and iterator, does not rely on the other layers. The framework's architecture is completely orthogonal. The relationship among the layers is acyclic. Lower layers do not depend nor know the existence of upper layers. Modules in a layer do not depend on other modules in the same layer.

The client may use only the modules that she wants without incurring any compile time nor run time penalty. A minimalistic approach is to use only the core as is. The highly streamlined core is usable by itself. The core is sufficiently suitable for tasks such as micro parsing.

The iterator module is independent of Spirit and may be used in other non-Spirit applications. This module is a compilation of stand-alone iterators and iterator wrappers compatible with Spirit. Over time, these iterators have been found to be most useful for parsing with Spirit.

The actor module, also independent of Spirit, is a compilation of predefined semantic actions that covers the most common semantics processing tasks.

The debug module provides library wide parser debugging. This module hooks itself up transparently into the core non-intrusively and only when necessary.

The attribute module introduces advanced semantic action machinery with emphasis on extraction and passing of data up and down the parser hierarchy through inherited and synthesized attributes. Attributes may also be used to actually control the parsing. Parametric parsers are a form of dynamic parsers that changes their behavior at run time based on some attribute or data.

The dynamic module focuses on parsers with behavior that can be modified at run-time.

error_handling. The framework would not be complete without Error Handling. C++'s exception handling mechanism is a perfect match for Spirit due to its highly recursive functional nature. C++ Exceptions are used extensively by this module for handling errors.

The symbols module focuses on symbol table management. This module is rather basic now. The goal is to build a sub-framework that will be able to accommodate C++ style multiple scope mechanisms. C++ is a great model for the complexity of scoping that perhaps has no parallel in any other language. There are classes and inheritance, private, protected and public access restrictions, friends, namespaces, using declarations, using directives, Koenig lookup (Argument Dependent Lookup) and more. The symbol table functionality we have now will be the basis of a complete facility that will attempt to model this.

> I wish that I could ever see, a structure as lovely as a tree...

Parse Tree and Abstract Syntax Tree (AST) generation are handled by the Tree module. There are advantages with Parse Trees and Abstract Syntax Trees over semantic actions. You can make multiple passes over the data without having to re-parse the input. You can perform transformations on the tree. You can evaluate things in any order you want, whereas with attribute schemes you have to process in a begin to end fashion. You do not have to worry about backtracking and action side effects that may occur with an ambiguous grammar.

The utility module is a set of commonly useful parsers and support classes that were found to be useful in handling common tasks such as list processing, comments, confix expressions, etc.

meta, provides metaprogramming facilities for advanced Spirit developers. This module facilitates compile-time and run-time introspection of Spirit parsers.

Copyright © 1998-2003 Joel de Guzman
Use, modification and distribution is subject to the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)