[erlang-questions] new json parser

Bob Ippolito <>
Fri Aug 8 18:22:43 CEST 2008


2008/8/8 Willem de Jong <>:
> Hi all,
>
> I have uploaded a json parser to trapexit.
> (http://forum.trapexit.org/viewtopic.php?p=44029#44029)
>
> More than anything else, the purpose of this parser is to convince Richard
> O'Keefe that having a json parser with a SAX-like API is a good idea. But
> fortunately it can also serve more practical purposes.
>
> As mentioned, the parser has a SAX-like API. It also has a mechanism to
> parse input data in blocks - if it reaches the end of the input data, it
> will call a function to provide the next block. The combination of these
> properties results in a parser that can process input of
> arbitrary size, or a stream of data.
>
> Included is a handler function that translates the SAX events into the same
> output format produced by mochijson2. Looks like this: {struct,
> [{<<"key1">>, <<"value1">>}, {<<"key2">>, 123}]}. Interestingly, the new
> parser (sax parser combined with handler) is roughly 2x as fast as
> mochijson2 (On my PC, at least).
>
> The parser consists of just 1 file, with some edoc documentation and a
> couple of very simple examples included. It only works on UTF-8 encoded
> input (which implies that it can also parse ASCII, of course).

I haven't profiled it but my guess is that yours is faster because it
doesn't keep track of the current character/line position in the doc.
mochijson2 does it because I like good error messages... :)

The second part is that mochijson2 is written such that it is
compatible with and performs well in R11B because that's what I was
using at the time. I'd have written it differently for R12B which
behaves very different with binaries (as far as performance goes).

-bob



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