A string parser like Rexx

[Pat Brown <whoopdedo@...>]

Any Rexx fans in the audience? I've always thought the PARSE format was a nice 
way to do basic pattern matching without all the complexity of a regex. I've 
put together a Lua implementation of the Rexx parser. It's still mostly 
experimental, I need more sample strings to test against. If you'd like to try 
it out, the work repo is https://github.com/ptbrown/rexxparse-lua

Use it like this:

rexxparse = require("rexxparse.parse")
result = rexxparse.parse(_VERSION, [["Lua" version.]])
print(result.version) -- 5.3

Or that's what it should be, that actually doesn't quite work as described 
yet. (It will complain about there not being a space before the dot.) But I'm 
getting there. Another way to do it is:

parser = rexxparse.parse[["Lua" version.]]
result = parser(_VERSION)
-- or
result = {}
parser(result, _VERSION)

The last one is for when you have a vref in the pattern. Rexx lets you use the 
value of a variable to make a match. Instead of "Lua" you might have the 
template [[(interpreter) version]] and it will read the value of (interpreter) 
from the same table it stores the result in. And if this is Lua 5.2 or 5.3, 
that table can be _ENV.

When using the two-argument form of rexxparse.parse, the table is the third 
argument. 

And finally, you can have multiple templates like this:

parser = rexxparse.parse[[ match1, match2, match3 ]]
results = parser(argument1, argument2, argument3)

This corresponds to the Rexx command PARSE ARG ... But I added a twist that 
Rexx didn't allow. A line break in the string will act the same as a comma, 
and all blank lines are ignored. That could also be written:

parser = rexxparse.parse[[
     match1
     match2
     match3
]]

Of course putting commas on each line anyway will be fine. 

So as you can see, it's a flexible function that I hope can be as close to the 
Rexx command as Lua will allow. With lots of fun bugs to be discovered. Again, 
the github URL is https://github.com/ptbrown/rexxparse-lua. 

Information about Rexx is at http://www.rexxinfo.org. A description of the 
Rexx parser is http://www.rexxla.org/events/2005/presentations/chipd.pdf 

And if I may hijack my own post, I just uploaded a module for working with 
fixed-width text files. It's called "flatfile" on LuaRocks.

(Pat Brown)