a structural comparison tool for Lisp programs

• Language-aware. ydiff parses programs, understands basic language constructs and will not make non-sensical comparisons. For example it will not compare a string "10000" with an integer 10000 even though they look very similar. Also, it tries to match functions with the same name before it attempts to destruct and compare functions of different names.

• Format insensitive. The comparison result will not be affected by different number of white spaces, line breaks or indentation. For example, ydiff will not produce a large diff just because you surrounded a block of code with if (condition) {...}.

• Moved code detection. ydiff can find refactored code -- renamed, moved, reordered, wrapped, lifted, combined or fragmented code. Refactored code can be detected however deep they are into the structures.

• Human-friendly output. The output of ydiff is designed for human understanding. The interactive UI helps the user navigate and understand changes efficiently.

ydiff originally aim to support multiple languages, but I found that the parsers are very boring and tedious to get right. I hate languages with complicated syntax which makes parsing hard, so I decided to stop developing parsers for languages except the Lisp family. The C++ parser here is just to demonstrate how a mostly-right C++ can be constructed within two days of work ;-) You are welcome to take the code and extend to complete parsing C++ and JavaScript, but I can't provide any assistance.

ydiff is implemented in Racket. You can get Racket from

http://racket-lang.org

To build ydiff, go to the directory containing the source and run

make

It should compile to several executables, such as diff-lisp, diff-cpp, diff-js etc. Copy those files to some directory in your PATH.

1. Run commands like this example:

    diff-lisp demos/mk1.ss demos/mk2.ss
   

   It will produce a HTML file named "mk1-mk2.html" in the current directory.

2. Use your browser to open the HTML file. That is basically it.

1. The HTML file needs the support files nav.js and diff.css to be present in the same directory. You must copy those files to the directory where you ran the commands. This is not a good user experience design and may be improved later.

Yin Wang ([email protected])

Copyright (C) 2011-2013 Yin Wang

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
3. The name of the author may not be used to endorse or promote products derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.