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+
+# adiff (arbitrary-tokens diff, patch and merge)
+
+This is a half-working pre-alpha version, use with care.
+
+### Short summary
+
+The main aim of this toolbox is to help with finding differences in text
+formats that do not have a fixed "line-by-line" semantics, as assumed by
+standard unix `diff` and related tools.
+
+The problem was previously tackled by Arek Antoniewicz on MFF CUNI, who
+produced a working software package in C++, and designed the Regex-edged DFAs
+(REDFAs) that were used for user-specifiable tokenization of the input. The
+work on the corresponding thesis is currently ongoing.
+
+This started as a simple Haskell port of that work, and packed some relatively
+orthogonal improvements (mainly the histogram-style diffing).
+
+### TODO list
+
+- Implement `patch` functionality (`diff` and `diff3` works)
+- Implement the splitting heuristic for diffs, so that the diffing of larger
+  files doesn't take aeons
+- Check whether REDFA can even be implemented correctly with current Haskell
+  libraries (most regex libraries target a completely different). Taking the
+  lexer specification format from `alex` currently seems like a much better
+  option. Deferring the task unix-ishly to another program could work too.
+
+# How-To
+
+Install using `cabal`. The `adiff` program has 3 sub-commands that work like
+`diff`, `patch` and `diff3`. It expects a lexing specification on the input;
+there are several very simple example lexers in `lexers/`.
+
+## Example
+
+Let's have a file `orig`:
+```
+Roses are red. Violets are blue.
+Patch is quite hard. I cannot rhyme.
+```
+
+and a modified file `mine`:
+```
+Roses are red. Violets are blue.
+Patching is hard. I still cannot rhyme.
+```
+
+Let's use the `words` lexer, which marks everything whitespace-ish as
+whitespace, and groups of non-whitespace:
+```
+:[^ \t\n]*
+_:[ \t\n]*
+```
+
+Diffing the 2 files gets done as such:
+```
+ $ cabal run adiff -- -l lexers/words diff orig mine
+```
+
+You should get something like this:
+```
+@@ -7 +7 @@
+ . 
+ |are
+ . 
+ |blue.
+ .\n
+-|Patch
++|Patching
+ . 
+ |is
+-. 
+-|quite
+ . 
+ |hard.
+ . 
+ |I
++. 
++|still
+ . 
+ |cannot
+ . 
+ |rhyme.
+ .\n
+```
+
+Let's pretend someone has sent us a patch with a better formated verse with
+some other improvements, in file `yours`:
+```
+Roses are red.
+Violets are blue.
+Patch is quite hard.
+I cannot do verses.
+```
+
+We can run `diff3` to get a patch with both changes, optionally with reduced
+context:
+```
+ $ cabal run adiff -- -l lexers/words diff3 mine orig yours -C1
+```
+...which outputs:
+```
+@@ -4 +4 @@
+ |red.
+-. 
++.\n
+ |Violets
+@@ -11 +11 @@
+ .\n
+-|Patch
++|Patching
+ . 
+ |is
+-. 
+-|quite
+ . 
+ |hard.
+-. 
++.\n
+ |I
++. 
++|still
+ . 
+@@ -23 +23 @@
+ . 
+-|rhyme.
++|do
++. 
++|verses.
+ .\n
+```
+
+...or get a merged output right away, using the `-m`/`--merge` option:
+```
+Roses are red.
+Violets are blue.
+Patching is hard.
+I still cannot do verses.
+```
+
+...or completely ignore whatever whitespace changes that the people decided to
+do for whatever reason, with `-i`/`--ignore-whitespace` (also works without
+`-m`):
+```
+Roses are red. Violets are blue.
+Patching is hard. I still cannot do verses.
+```
+
+If there's a conflict (substituing the `Patch` to `Merging` in file `yours`), it gets highlighted in the merged diff as such:
+```
+[...]
+ . 
+ |blue.
+ .\n
+<|Patching
+=|Patch
+>|Merging
+ . 
+ |is
+-. 
+-|quite
+[...]
+```
+
+and using the standard conflict marks in the merged output:
+```
+Roses are red.
+Violets are blue.
+<<<<<<<Patching|||||||Patch=======Merging>>>>>>> is hard.
+I still cannot do verses.
+```
diff --git a/lexers/letters b/lexers/letters
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+++ b/lexers/letters
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+[a-z]
+_:[ \n]
diff --git a/lexers/lines b/lexers/lines
new file mode 100644
index 0000000..5bf4719
--- /dev/null
+++ b/lexers/lines
@@ -0,0 +1,2 @@
+[^\n]*\n
+[^\n]*
diff --git a/lexers/nums b/lexers/nums
new file mode 100644
index 0000000..3e57b7e
--- /dev/null
+++ b/lexers/nums
@@ -0,0 +1,2 @@
+[0-9]
+_:\n
diff --git a/lexers/words b/lexers/words
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--- /dev/null
+++ b/lexers/words
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+:[^ \t\n]*
+_:[ \t\n]*