IPInfoDB

Providing location-based services is all the rage these days. On the newer mobile devices, there are services that use GPS and nearby cellular towers to improve your user experience with the knowledge of where you are at any moment.

In the wild internet, there hasn't been many convenient ways to do this, but a recent website called IPInfoDB (previously known as "IP Location Tools"), provides an API for mapping an IP address to a physical address. The API consists of a PHP page that returns an XML response that contains your location, or the location of an IP address that you provide. They also seem to support CSV and JSON responses.

For example, to lookup the location of an IP address used by google.com:

http://ipinfodb.com/ip_query.php?ip=74.125.45.100

Curious to see how easily it would be to use this API from Factor, I wrote a vocabulary for accessing IPInfoDB.

First, we define the characteristics of an ip-info tuple.

TUPLE: ip-info ip country-code country-name region-code
region-name city zip-code latitude longitude gmtoffset
dstoffset ;

The API returns XML response, which we need to convert into an ip-info object. For this, we use the excellent XML parsing vocabulary that has seen a lot of improvements recently.

: find-tag ( tag name -- value )
    deep-tag-named children>string ; inline

: xml>ip-info ( xml -- info )
    [ ip-info new ] dip
    {
        [ "Ip" find-tag >>ip ]
        [ "CountryCode" find-tag >>country-code ]
        [ "CountryName" find-tag >>country-name ]
        [ "RegionCode" find-tag >>region-code ]
        [ "RegionName" find-tag >>region-name ]
        [ "City" find-tag >>city ]
        [ "ZipPostalCode" find-tag >>zip-code ]
        [ "Latitude" find-tag >>latitude ]
        [ "Longitude" find-tag >>longitude ]
        [ "Gmtoffset" find-tag >>gmtoffset ]
        [ "Dstoffset" find-tag >>dstoffset ]
    } cleave ;

With that done, it is very easy to make an http request to retrieve one's own location:

: locate-my-ip ( -- info ) 
    "http://ipinfodb.com/ip_query.php"
    http-get string>xml xml>ip-info nip ;

Or determine the location of any arbitrary IP:

: locate-ip ( ip -- info )
    "http://ipinfodb.com/ip_query.php?ip=" prepend
    http-get string>xml xml>ip-info nip ;

The example I showed earlier would be:

( scratchpad ) "74.125.45.100" locate-ip .
T{ ip-info
    { ip "74.125.45.100" }
    { country-code "US" }
    { country-name "United States" }
    { region-code "06" }
    { region-name "California" }
    { city "Mountain View" }
    { zip-code "94043" }
    { latitude "37.4192" }
    { longitude "-122.057" }
    { gmtoffset "-8.0" }
    { dstoffset "-7.0" }
}

Presumably, if this code were to be used more frequently, it would need some error handling for when the http server is not available, or non-responsive.

Anyway, this vocabulary is available on my GitHub

Brainf*ck

The Brainfuck programming language is a curious invention. Seemingly useful only for proving oneself as a True Geek at a party, it could also be useful for educational purposes.

The first programming example in any language is typically "Hello, world!". In Brainfuck, this could be written as:

++++++++++[>+++++++>++++++++++>+++>+<<<<-]
>++.>+.+++++++..+++.>++.<<+++++++++++++++
.>.+++.------.--------.>+.>.

For fun, I thought I would build a Brainfuck compiler for Factor.

( scratchpad ) USE: brainfuck

( scratchpad ) "
               ++++++++++[>+++++++>++++++++++>+++>+<<<<-]
               >++.>+.+++++++..+++.>++.<<+++++++++++++++
               .>.+++.------.--------.>+.>.
               " run-brainfuck
Hello World!

Behind the scene, the Brainfuck code is being compiled into proper Factor using a macro that parses the Brainfuck code string. When translated into Factor, the "Hello, world!" example becomes:

<brainfuck>
10 (+) [ (?) ] [
    1 (>) 7 (+) 1 (>) 10 (+) 1 (>) 3 (+)
    1 (>) 1 (+) 4 (<) 1 (-)
] while
1 (>) 2 (+) (.) 1 (>) 1 (+) (.)
7 (+) (.) (.) 3 (+) (.) 1 (>) 2 (+) (.)
2 (<) 15 (+) (.) 1 (>) (.) 3 (+)
(.) 6 (-) (.) 8 (-) (.) 1 (>) 1 (+) (.) 
1 (>) (.) drop flush

I made only a slight optimization, which you might notice above, to collapse a series of identical operators together into a single call to the operator word, while staying true to the original set of Brainfuck operators.

Some fun examples of Brainfuck in the brainfuck-tests.factor unit tests include addition, multiplication, division, uppercase, and a cat utility.

It is available on my Github, and hopefully will be pulled into the main repository soon.