STX Expression Parser C++ Framework
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             *** STX Expression Parser C++ Framework v0.7  ***

Author: Timo Bingmann (Mail: tb a-with-circle idlebox dot net)
Date: 2007-07-17

--- Summary ---

The STX Expression Parser provides a C++ framework, which can process
user-specified expression strings containing program-specific variables. It can
be integrated into applications to allow user-customized data selection and
filtering. The expresssion strings are intuitive SQL-like WHERE-clauses and can
contain arbitrarily complex arithmetic. At the same time the expression
processing time is guaranteed to be fast enough to safely iterate over larger
data sets.

Originally I wrote this parser framework for my study thesis (see In the thesis millions
of graph edges are processed and organized in an r-tree search index
structure. Each vertex and edge had a number of attributes like "color" or
"importance". These attributes could then be used in filter expressions to
determine which edges are returned by a graph server and displayed on a remote
client. The attributes of the filtered edges could be used to calculate the
returned data set using expressions similar to SQL column selection clauses.

Four instructive example applications are included in the package. See
"Extensive Example Programs Including Source Code" for more.

--- Website / API Docs / Bugs / License ---

The current source distribution package can be downloaded from

The library source and example programs are extensively documented using
doxygen. The compiled doxygen HTML documentation can be found at

If bugs should become known they will be posted on the above web page together
with patches or corrected versions.

The complete source code is released under the GNU Lesser General Public
License v2.1 (LGPL) which can be found in the file COPYING.

--- Demo and Example Programs ---

The wxWidgets parser demo program is located in the directory
wxparserdemo. Compiled binary versions can be found on the package web page.

Further example code is located in the examples/ directory and is extensively
commented within the doxygen html pages.

An online interactive CGI version of the parser can be accessed at . It displays the inner
workings of the library for a given expression string.

Furthermore a number of example CSV data files can be browsed, sorted, analyzed
and filtered using the csvtool example. See
for an instructive use of this library.

--- Compilation and Boost.Spirit ---

The expression parser's grammar is implemented using the Boost.Spirit parser
framework (see Therefore Boost must be
installed to compile the expression parser library. But as Boost.Spirit is a
set template includes, the resulting static library has no external
dependencies. The second purpose of this library release is to show a
reasonably complex Spirit parser grammar. See "Spirit Grammar and ParseTree
Processing" for more details.

  Compiling the library with gcc 3.3 -O3 can take very long and a huge amount
  of RAM. This is due to the complex template classes created by
  Boost.Spirit. Compilation with gcc 4.x is much faster.

--- Expression Examples ---

The expression parser allows arbitrarily complex arithmetic expressions like:

  6 + 3 * 12
  (5 + 3) * 5.25
  (int)(30 * 1.4)
  (5 + 1 + 1 + 1) * (4.25 + 0.4 * 2.5 / (3.1 - 0.525 * 4))

To process program-defined data functions and variables may be included in the

  a * 5 + 3 * b + EXP( LOGN(2) ) + COS( PI() / 2 )

To enable the expressions to be used as filters many comparison operators and
boolean logic operators are defined:

  6 * 9 == 42
  a >= 5 OR (42 <= field2 AND field2 <= 48) || NOT(got == "yes")

--- Extensive Example Programs Including Source Code ---

The distribution contains two well documented example programs:

  * exprcalc: A Simple Expression Calculator
  * csvfilter: A CSV-File Record Filter

and a third more complex (less documented) example program:

  * csvtool: An Enhanced CSV-File Record Filter and Sorter

Furthermore a user-friendly graphical demonstration application is included:

  * wxParserDemo: wxWidgets Demo Application

--- Short Overview of the Library's Design ---

-- Types and the AnyScalar Class --

The parser operates on following scalar types:

  * boolean
  * 8-bit 'char' integer, 16-bit 'short', 32-bit 'integer' and 64-bit 'long'
  * 8-bit 'byte', 16-bit 'word', 32-bit 'dword' and 64-bit 'qword' unsigned
  * single and double precision floating point (float and double).
  * string

These data types are processed by the library using the stx::AnyScalar
class. It contains a (type, value) pair of one of the scalar type listed
above. These scalar values can then be added, subtracted, multiplied, divided
or compared using member functions. If the two composed scalar objects are of
unequal type, then the operation is calculated in the "higher" data type (very
similar to C) and returned as such. So a small unsigned integer can be added to
a larger integer or even a string.

The reason to include the smaller integer types is based on the original
purpose of this library. In my study thesis the resulting values were
transfered over a network socket from a graph server to its drawing client. For
this purpose it was important to convert the resulting values into smaller data
types and thus reduce network traffic. For online-filtering applications this
is probably not as important.

-- Spirit Grammar and ParseTree Processing -- 

The expression parser grammar is an extension of the more basic "arithmetic
calculator". It is extended to recognize floating point numbers, quoted string
constants, attribute placeholders, function calls, comparison and boolean

A user given input string is parsed by Spirit into an abstract syntax tree
(AST). The AST is then processed into a tree of stx::ParseNode objects. During
the construction of the stx::ParseNode objects all constant subtrees are folded
into constant objects. This way repeated evaluation of the ParseTree is
accelerated. At the end the top stx::ParseNode is returned in a stx::ParseTree

The stx::ParseTree's main method is evaluate(), which takes a stx::SymbolTable
and recursively evaluates the contained stx::ParseNode tree using the variable
and functions contained in the symbol table. The result is returned as an
stx::AnyScalar object.

-- Further Details --

After this abstract design discussion it is probably best to read the first
"Example Application: Simple Expression Calculator". It contains a
comprehensible walk-through of the libraries interface function and classes.