BNF-like grammar specified DIRECTLY in Ruby

[Eric Mahurin]

Here is my first contribution to Ruby:

http://raa.ruby-lang.org/project/syntax/

There is still plenty missing in here and it is a work in
progress, but I think it is ready for some of you to try it out
if you like it.

To get an idea of what this is, there is a simple expression
evaluator example below. This is pure Ruby code - no yacc type
compiling necessary. That's what I love about it.

Eric


#!/usr/bin/ruby -d

require "syntax"

NULL = Syntax::NULL
INF = +1.0/0
LOOP0 = (0..INF)
LOOP1 = (1..INF)

int = (("0".."9")*LOOP1).qualify { |m| m.to_s.to_i }

number = (
int +
(("."+int)|NULL) +
((("e"|"E")+("+"|"-"|NULL)+int)|NULL)
).qualify { |m|
if (m.length>1)
m.to_s.to_f
else
m[0]
end
}

ws = ((" "|"\t"|"\n")*LOOP0).qualify { TRUE } # skipped with
TRUE

expr = Syntax:ass.new # need to predefine object for
recursion

atom =
(number+ws).qualify{|m|m[0]} |
("(" + expr + ")" + ws).qualify{|m|m[1]}

term = (
atom + ( ("*"|"/"|"%") + ws + atom )*LOOP0
).qualify { |m|
product = m[0]
m[1].each { |m|
case m[0]
when "*" then product *= m[1]
when "/" then product /= m[1]
when "%" then product %= m[1]
end
}
product
}

expr << (
ws + term + ( ("+"|"-") + ws + term )*LOOP0
).qualify { |m|
sum = m[0]
m[1].each { |m|
case m[0]
when "+" then sum += m[1]
when "-" then sum -= m[1]
end
}
sum
}

while (gets)
p(expr===RandomAccessStream.new($_))
end






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[Jamis Buck]

Very nice! One quibble: any chance you could change the name?

http://rubyforge.org/projects/syntax

Might get confusing if someone wants to install both libs.

- Jamis

 

[Takaaki Tateishi]

Here is my first contribution to Ruby:
http://raa.ruby-lang.org/project/syntax/

Let me inform you that I'm also developing similar library TDP4R.
http://rubyforge.org/projects/tdp4r
Some examples are available at:
http://rubyforge.org/cgi-bin/viewcvs.cgi/tdp4r/samples/?cvsroot=tdp4r

Thanks,