REfO
====
Lacking a proper name, REfO stands for "Regular Expressions for Objects".
It's a python library that supplies a functionality very similar to the python
`re` module (regular expressions) but for arbitrary sequences of objects
instead of strings (sequences of characters).
In addition to that, it's possible to match each object in a sequence with
not only equality, but an arbitrary python function.
For example, if you have a sequence of integers you can make a regular
expression that asks for a even number followed by a prime number
followed by a 3-divisible number.
This software was written by Rafael Carrascosa while working at Machinalis in
the first months of 2012.
Contact: rcarrascosa@machinalis.com
or rafacarrascosa xyz gmail.com (replace " xyz " with "@")
[](https://travis-ci.org/gjhiggins/refo)
How to use it
-------------
The syntax is a little bit different than python's re, and similar to that of
pyparsing, you have to more-or-less explicitly build the syntax tree of
your regular expression. For instance:
`"ab"` is `Literal("a") + Literal("b")`
`"a*"` is `Star(Literal("a"))`
`"(ab)+|(bb)*?"` is:
a = Literal("a")
b = Literal("b")
regex = Plus(a + b) | Star(b + b, greedy=False)
You can also assign a group to any sub-match and later on retrieve the matched
content, for instance:
regex = Group(Plus(a + b), "foobar") | (b + b)
m = match(regex, "abab")
print m.span("foobar") # prints (0, 4)
For more, check out the examples in the examples folder.
How we use it
-------------
At Machinalis we use REfO for applications similar to that in
`examples/words.py`, check it out!
About the implementation
------------------------
I use a Thompson-like virtual machine aproach, which ensures polynomial time
worst-case complexity. See `examples/poly_time.py` for an example of this.
The implementation is heavily based on Russ Cox notes, see
http://swtch.com/~rsc/regexp/regexp2.html for the source.
If you go to read the code, some glossary:
- RE -- regular expression
- VM -- virtual machine
- Epsilon transitions -- All VM instructions that do not consume a symbol
or stop the thread (for example an Accept).
Acknowledgements
----------------
Thanks Russ Cox for sharing the awesome info and insights on your web site.
Thanks Javier Mansilla for reviewing the code and being enthusiastic about it.
Thanks Machinalis for everything :)
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