The three rules of Ruby Q.:
-
Please do not post any solutions or spoiler discussion for this quiz
until
48 hours have passed from the time on this message. -
Support Ruby Q. by submitting ideas as often as you can:
- Enjoy!
Suggestion: A [QUIZ] in the subject of emails about the problem helps
everyone
on Ruby T. follow the discussion. Please reply to the original quiz
message,
if you can.
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
There has been a lot of talk recently about parsing with Ruby. We’re
seeing
some parser generator libraries pop up that make the task that much
easier and
they’ve been stirring up interest.
In honor of that, this week’s Ruby Q. is to write a parser for JSON.
JSON turns out to turns out to be a great little example for writing
parsers for
two reasons. First, it’s pretty easy stuff. You can hand-roll a JSON
parser in
under 100 lines of Ruby. The second advantage is that the data format
is
wonderfully documented:
Since JSON is just a data format and Ruby supports all of the data
types, I vote
we just use Ruby itself as the abstract syntax tree produced by the
parse.
Feel free to show off your favorite parser generator, if you don’t want
to roll
your own. Anything goes.
Here are a few tests to get you started:
require “test/unit”
class TestJSONParser < Test::Unit::TestCase
def setup
@parser = JSONParser.new
end
def test_keyword_parsing
assert_equal(true, @parser.parse("true"))
assert_equal(false, @parser.parse("false"))
assert_equal(nil, @parser.parse("null"))
end
def test_number_parsing
assert_equal(42, @parser.parse("42"))
assert_equal(-13, @parser.parse("-13"))
assert_equal(3.1415, @parser.parse("3.1415"))
assert_equal(-0.01, @parser.parse("-0.01"))
assert_equal(0.2e1, @parser.parse("0.2e1"))
assert_equal(0.2e+1, @parser.parse("0.2e+1"))
assert_equal(0.2e-1, @parser.parse("0.2e-1"))
assert_equal(0.2E1, @parser.parse("0.2e1"))
end
def test_string_parsing
assert_equal(String.new, @parser.parse(%Q{""}))
assert_equal("JSON", @parser.parse(%Q{"JSON"}))
assert_equal( %Q{nested "quotes"},
@parser.parse('"nested \"quotes\""') )
assert_equal("\n", @parser.parse(%Q{"\\n"}))
assert_equal( "a",
@parser.parse(%Q{"\\u#{"%04X" % ?a}"}) )
end
def test_array_parsing
assert_equal(Array.new, @parser.parse(%Q{[]}))
assert_equal( ["JSON", 3.1415, true],
@parser.parse(%Q{["JSON", 3.1415, true]}) )
assert_equal([1, [2, [3]]], @parser.parse(%Q{[1, [2, [3]]]}))
end
def test_object_parsing
assert_equal(Hash.new, @parser.parse(%Q{{}}))
assert_equal( {"JSON" => 3.1415, "data" => true},
@parser.parse(%Q{{"JSON": 3.1415, "data": true}}) )
assert_equal( { "Array" => [1, 2, 3],
"Object" => {"nested" => "objects"} },
@parser.parse(<<-END_OBJECT) )
{"Array": [1, 2, 3], "Object": {"nested": "objects"}}
END_OBJECT
end
def test_parse_errors
assert_raise(RuntimeError) { @parser.parse("{") }
assert_raise(RuntimeError) { @parser.parse(%q{{"key": true
false}}) }
assert_raise(RuntimeError) { @parser.parse("[") }
assert_raise(RuntimeError) { @parser.parse("[1,,2]") }
assert_raise(RuntimeError) { @parser.parse(%Q{"}) }
assert_raise(RuntimeError) { @parser.parse(%Q{"\\i"}) }
assert_raise(RuntimeError) { @parser.parse("$1,000") }
assert_raise(RuntimeError) { @parser.parse("1_000") }
assert_raise(RuntimeError) { @parser.parse("1K") }
assert_raise(RuntimeError) { @parser.parse("unknown") }
end
end
