foo.treetop

grammar Foo
    rule top
        value? {
            def to_ruby
                elements.to_ruby
            end
        }
    end
    rule value
        array / object / primitive
    end
    rule primitive
        null / true / false / string / float / integer
    end
    rule object
        "{" space head:pair space tail:("," space pair)* space "}" {
            def to_ruby
                Hash[tail.elements.map(&:pair).map(&:to_ruby).unshift(head.to_ruby)]
            end
        }
        /
        "{" space "}" {
            def to_ruby
                {}
            end
        }
    end
    rule pair
        k:primitive space ":" space v:value {
            def to_ruby
                [ k.to_ruby, v.to_ruby ]
            end
        }
    end
    rule array
        "[" space head:value space tail:("," space value)* space "]" {
            def to_ruby
                tail.elements.map(&:value).map(&:to_ruby).unshift(head.to_ruby)
            end
        }
        /
        "[" space "]" {
            def to_ruby
                []
            end
        }
    end
    rule null
        space "null" space {
            def to_ruby
                nil
            end
        }
    end
    rule true
        space "true" space {
            def to_ruby
                true
            end
        }
    end
    rule false
        space "false" space {
            def to_ruby
                false
            end
        }
    end
    rule string
        '"' [a-zA-Z0-9 _-]* '"' {
            def to_ruby
                text_value.gsub(/\"/,"")
            end
        }
    end
    rule float
        [+-]? [0-9]* "." [0-9]* {
            def to_ruby
                text_value.to_f
            end
        }
    end
    rule integer
        [+-]? [0-9]+ {
            def to_ruby
                text_value.to_i
            end
        }
    end
    rule space
        [ \t\r\n]*
    end
end

jsonify.rb

#!/usr/bin/env ruby
$:.unshift "."
require "treetop"
require "foo"
require "pp"

pp FooParser.new.parse('null').to_ruby
pp FooParser.new.parse('true').to_ruby
pp FooParser.new.parse('false').to_ruby
pp FooParser.new.parse('"hello"').to_ruby
pp FooParser.new.parse('1').to_ruby
pp FooParser.new.parse('0').to_ruby
pp FooParser.new.parse('-1').to_ruby
pp FooParser.new.parse('.230').to_ruby
pp FooParser.new.parse('023.').to_ruby
pp FooParser.new.parse('023.230').to_ruby

pp FooParser.new.parse('[ ]').to_ruby
pp FooParser.new.parse('[1,2,3]').to_ruby
pp FooParser.new.parse('[1.1,2.2,3.3]').to_ruby
pp FooParser.new.parse('["hello"]').to_ruby
pp FooParser.new.parse('[ "hello" , "world" ]').to_ruby
pp FooParser.new.parse('[ true, false, null, 1, 1.2, "string" ]').to_ruby

pp FooParser.new.parse('{ }').to_ruby
pp FooParser.new.parse('{"hello":"world"}').to_ruby
pp FooParser.new.parse('{"hello":"world", "foo":"bar", "shelling":"ford"}').to_ruby
pp FooParser.new.parse('{ true : null, false : null }').to_ruby

pp FooParser.new.parse('[{"hello":"world"}, {"foo":"bar"}, {"shelling":"ford"}]').to_ruby
pp FooParser.new.parse('{"list" : [1,2,3]}').to_ruby