ASDF-install package (obsolete) https://github.com/froydnj/diff/tarball/master NOTE: Old rice.edu link broken as of 12/31/2009. Code has reappeared on github at https://github.com/froydnj/diff - tried changing the link above to pull a tarball of the master branch, no idea if it will work.
DIFF is a simple asdf-installable Text library which can compute unified-style or context-style diffs between two files. It also includes code to compute copy/insert deltas via the vdelta algorithm and encode those diffs in svndiff format. Other algorithms and encodings are planned for future versions. Version 0.4 includes a reader for "patch" files; an interface for applying patches is planned for future versions. Comments on the interface or wanted algorithms greatly appreciated.