apatch is an implementation of associative text patching in OCaml. My theory and motivation for associative patching is alread laid out decently at adiff, the project for my Clojure implementation. To understand this project, you can skip the part about "Nested Patches", since it doesn't matter for text and I'm not sure how sound it is. The main difference for this project is that I have implemented the run-length encoding optimization mentioned in the "what about real life?" section.
The text format for patches is pretty simple.
It's a %[D13]beautiful day. %[K34]
We can do literal \%[K3] too.
The %[...] syntax introduces what I call a "reader form", a patch element
that either reads in or ignores/deletes characters from the source. As you
might guess, %[D13] drops 13 characters and %[K34] copies in 34
characters. \%[ results in a simple insertion of %[, so you can write
patches for documents that talk about patches. The %[..] syntax was chosen
for minimal interference with other languages.
First, compile. If you have OCaml installed on your system, you can simply
make all, which builds apply and the test programs.
If you want to do patching in an OCaml program, test.ml has a number of
examples of creating and applying patches.
Using the command-line apply program is pretty simple. In short:
./apply patch < source > result. You can try this with the included
patch files:
$ ./apply patchy.patch < sourcy.patch
ABCabcd
Watch out for implicit newlines at the end of files. If you get a mysterious "dangling insert" error, try increasing the size of a reader form in the patch by 1.
Obviously, these sorts of patches are not much fun to write by hand. Someday I'll get around to implementing diffing. Also, both "adiff" and "apatch" are pretty lame names, and I need to invent a better one.