[ragel-users] ragel scanner construct question

Pramukta Kumar prak at mac.com
Mon Apr 20 22:26:11 UTC 2009

I am experimenting with ragel to validate and tokenize an algebraic  
expression in one step.  Basically convert something like "3 + A * 2 /  
( 1 - 5 )" to "[3.0, 'A' , 2.0, :*, 1.0, 5.0, :-, :/, :+]" if it's  
valid, and throw an error otherwise. I'm using the ruby target, and  
the standard "shunting yard" algorithm or whatever.

I have the thing working (I think, still testing) by using the scanner  
construct and making an "allowed transition" table by hand.  Each of  
the tokenizing actions validates against this table to see whether it  
should continue.  It seems to me that there is probably a nice way to  
do this within ragel itself but I can't seem to figure it out.  Can  
somebody point me in the right direction?

the files are up on github: http://github.com/prakatmac/expression-parser/tree/master

Sorry if this is a dumb question.  I'm pretty new at this stuff.   


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