Bowling Scores

Today we are going to explore building a bowling score calculator using Factor. In particular, we will be scoring ten-pin bowling.

There are a lot of ways to "golf" this, including this short version in F#, but we will build this in several steps through transformations of the input. The test input is a string representation of the hits, misses, spares, and strikes. The output will be a number which is your total score. We will assume valid inputs and not do much error-checking.

A sample game might look like this:

12X4--3-69/-98/8-8-

Our first transformation is to convert each character to a number of pins that have been knocked down for each ball. Strikes are denoted with X, spares with /, misses with -, and normal hits with a number.

: pin ( last ch -- pin )
    {
        { CHAR: X [ 10 ] }
        { CHAR: / [ 10 over - ] }
        { CHAR: - [ 0 ] }
        [ CHAR: 0 - ]
    } case nip ;

We use this to convert the entire string into a series of pins knocked down for each ball.

: pins ( str -- pins )
    f swap [ pin dup ] { } map-as nip ;

A single frame will be either one ball, if a strike, or two balls. We are going to use cut-slice instead of cut because it will be helpful later.

: frame ( pins -- rest frame )
    dup first 10 = 1 2 ? short cut-slice swap ;

A game is 9 "normal" frames and then a last frame that could have up to three balls in it.

: frames ( pins -- frames )
    9 [ frame ] replicate swap suffix ;

Some frames will trigger a bonus. Strikes add the value of the next two balls. Spares add the value of the next ball. We build this by "un-slicing" the frame and calling sum on the next balls.

: bonus ( frame -- bonus )
    [ seq>> ] [ to>> tail ] [ length 3 swap - ] tri head sum ;

We can score the frames by checking for frames where all ten pins are knocked down (either spares or strikes) and adding their bonus.

: scores ( frames -- scores )
    [ [ sum ] keep over 10 = [ bonus + ] [ drop ] if ] map ;

We can solve the original goal by just adding all the scores:

: bowl ( str -- score )
    pins frames scores sum ;

And write a bunch of unit tests to make sure it works:

{ 0 } [ "---------------------" bowl ] unit-test
{ 11 } [ "------------------X1-" bowl ] unit-test
{ 12 } [ "----------------X1-" bowl ] unit-test
{ 15 } [ "------------------5/5" bowl ] unit-test
{ 20 } [ "11111111111111111111" bowl ] unit-test
{ 20 } [ "5/5-----------------" bowl ] unit-test
{ 20 } [ "------------------5/X" bowl ] unit-test
{ 40 } [ "X5/5----------------" bowl ] unit-test
{ 80 } [ "-8-7714215X6172183-" bowl ] unit-test
{ 83 } [ "12X4--3-69/-98/8-8-" bowl ] unit-test
{ 150 } [ "5/5/5/5/5/5/5/5/5/5/5" bowl ] unit-test
{ 144 } [ "XXX6-3/819-44X6-" bowl ] unit-test
{ 266 } [ "XXXXXXXXX81-" bowl ] unit-test
{ 271 } [ "XXXXXXXXX9/2" bowl ] unit-test
{ 279 } [ "XXXXXXXXXX33" bowl ] unit-test
{ 295 } [ "XXXXXXXXXXX5" bowl ] unit-test
{ 300 } [ "XXXXXXXXXXXX" bowl ] unit-test
{ 100 } [ "-/-/-/-/-/-/-/-/-/-/-" bowl ] unit-test
{ 190 } [ "9/9/9/9/9/9/9/9/9/9/9" bowl ] unit-test

This is available on my GitHub.

Haikunator

The Haikunator is a project to provide "Heroku-like memorable random names". These names usually consist of an adjective, a noun, and a random number or token. The original repository is implemented in Ruby, with ports to Go, Javascript, Python, PHP, Elixer, .NET, Java, and Dart.

We will be implementing this in Factor using the qw vocabulary that provides a simple way to make "arrays of strings" using the qw{ syntax.

First, a list of adjectives:

CONSTANT: adjectives qw{
    autumn hidden bitter misty silent empty dry dark summer icy
    delicate quiet white cool spring winter patient twilight
    dawn crimson wispy weathered blue billowing broken cold
    damp falling frosty green long late lingering bold little
    morning muddy old red rough still small sparkling throbbing
    shy wandering withered wild black young holy solitary
    fragrant aged snowy proud floral restless divine polished
    ancient purple lively nameless lucky odd tiny free dry
    yellow orange gentle tight super royal broad steep flat
    square round mute noisy hushy raspy soft shrill rapid sweet
    curly calm jolly fancy plain shinny
}

Next, a list of nouns:

CONSTANT: nouns qw{
    waterfall river breeze moon rain wind sea morning snow lake
    sunset pine shadow leaf dawn glitter forest hill cloud
    meadow sun glade bird brook butterfly bush dew dust field
    fire flower firefly feather grass haze mountain night pond
    darkness snowflake silence sound sky shape surf thunder
    violet water wildflower wave water resonance sun wood dream
    cherry tree fog frost voice paper frog smoke star atom band
    bar base block boat term credit art fashion truth disk
    math unit cell scene heart recipe union limit bread toast
    bonus lab mud mode poetry tooth hall king queen lion tiger
    penguin kiwi cake mouse rice coke hola salad hat
}

We will make a token out of digits:

CONSTANT: token-chars "0123456789"

Finally, a simple haikunate implementation:

: haikunate ( -- str )
    adjectives random
    nouns random
    4 [ token-chars random ] "" replicate-as
    "%s-%s-%s" sprintf ;

We can try it a few times, to see how it works:

IN: scratchpad haikunate .
"odd-water-8344"

IN: scratchpad haikunate .
"flat-tooth-9324"

IN: scratchpad haikunate .
"wandering-lion-8346"

IN: scratchpad haikunate .
"yellow-mud-9780"

IN: scratchpad haikunate .
"patient-unit-4203"

IN: scratchpad haikunate .
"floral-feather-1023"

Some versions of "haikunate" in other languages include features such as:

• allow customization of the delimiter (dots are popular)
• allow the token to be specified as a range of possible numbers
• allow the token to be restricted to a maximum length
• allow the token to be represented using hex digits
• allow the token to be represented with custom character sets
• etc.

This is available on my GitHub.

Random Desktop Background

As a follow-up to my Desktop Background post, I wanted to show how to set your desktop background to random images from various online image sites. We will be downloading a URL to a local file and then setting the desktop picture to that file:

: download-and-set-desktop-picture ( url -- )
    dup "/" split1-last nip cache-file
    [ download-to ] [ set-desktop-picture ] bi ;

Okay, now we need some random images!

Imgur is a huge image-hosting website frequently used on sites like Reddit.

: random-imgur ( -- url )
    "https://imgur.com/random" scrape-html nip
    "image_src" "rel" find-by-attribute-key-value
    first "href" attribute ;

XKCD has some fun comics. Maybe they would look good on the desktop!

: random-xkcd ( -- url )
    "http://dynamic.xkcd.com/random/comic/" http-get nip
    R@ http://imgs\.xkcd\.com/comics/[^\.]+\.(png|jpg)@
    first-match >string ;

WallpaperStock has a bunch of more traditional desktop images. We will scrape their random wallpaper page, find the first wallpaper thumbnail, load that wallpaper page, find the default image page, and then load that to find the image URL.

: random-wallpaperstock ( -- url )
    "http://wallpaperstock.net/random-wallpapers.html"
    scrape-html nip "wallpaper_thumb" find-by-class-between
    "a" find-by-name nip "href" attribute
    "http://wallpaperstock.net" prepend scrape-html nip
    "the_view_link" find-by-id nip "href" attribute
    "http:" prepend scrape-html nip "myImage" find-by-id nip
    "src" attribute "http:" prepend ;

Using this is as easy as:

IN: scratchpad random-imgur
               download-and-set-desktop-picture

IN: scratchpad random-xkcd
               download-and-set-desktop-picture

IN: scratchpad random-wallpaperstock
               download-and-set-desktop-picture

This is available on my GitHub.

Desktop Background

One of the benefits of learning to program is learning how to automate tasks performed with a computer. I thought it might be fun to build a simple vocabulary to allow getting and setting of the desktop background picture. Since Factor makes it pretty easy to build cross-platform vocabularies, we will implement this on Mac OS X, Linux, and Windows.

Our API consists of two words, one that gets the current desktop picture and one that sets a new desktop picture, dispatching based on which operating system we are running on (technically, based on the value of the os variable).

HOOK: get-desktop-picture os ( -- path )

HOOK: set-desktop-picture os ( path -- )

Mac OS X

On Mac OS X, we use AppleScript to ask the Finder what the path to the current desktop picture is, or tell it to set the desktop picture to a specific path.

M: macosx get-desktop-picture
    {
        "osascript" "-e"
        "tell app \"Finder\" to get posix path of (get desktop picture as alias)"
    } utf8 [ readln ] with-process-reader ;

M: macosx set-desktop-picture
    absolute-path
    "tell application \"Finder\" to set desktop picture to POSIX file \"%s\""
    sprintf run-apple-script ;

Windows

On Windows, we use the SystemParametersInfo function to get and set the desktop wallpaper.

CONSTANT: SPI_GETDESKWALLPAPER 0x0073

CONSTANT: SPI_SETDESKWALLPAPER 0x0014

M: windows get-desktop-picture
    SPI_GETDESKWALLPAPER MAX_PATH dup 1 + WCHAR <c-array> [
        0 SystemParametersInfo win32-error<>0
    ] keep alien>native-string ;

M: windows set-desktop-picture
    [ SPI_SETDESKWALLPAPER 0 ] dip utf16n encode
    0 SystemParametersInfo win32-error<>0 ;

Linux

On Linux, which has many different desktops, we are going to assume a GNOME environment. Other window managers have different ways to change the desktop background.

M: linux get-desktop-picture
    {
        "gsettings"
        "get"
        "org.gnome.desktop.background"
        "picture-uri"
    } utf8 [ readln ] with-process-reader
    "'file://" ?head drop "'" ?tail drop ;

M: linux set-desktop-picture
    {
        "gsettings"
        "set"
        "org.gnome.desktop.background"
        "picture-uri"
    } swap absolute-path "file://" prepend suffix try-process ;

This is available on my GitHub.

Automated Reasoning

There was a post about Automated Reasoning in F#, Scala, Haskell, C++, and Julia that uses a simple algorithm from John Harrison's book Handbook of Practical Logic and Automated Reasoning to simplify this equation:

e = (1 + (0 * x)) * 3) + 12

Factor has support for ML-style pattern matching and I thought it would be fun to contribute a simple solution using the match vocabulary.

We want to define a few types of expressions:

TUPLE: Var s ;
TUPLE: Const n ;
TUPLE: Add x y ;
TUPLE: Mul x y ;

Note: we could have made this simpler by assuming integers are constants and strings are variables rather than define the Const and Var tuples, but I wanted to keep this close to the code in the original blog post.

To be able to pattern match, we need to define some match variables:

MATCH-VARS: ?x ?y ;

We want a way to do a single simplification of an expression:

: simplify1 ( expr -- expr' )
    {
        { T{ Add f T{ Const f 0 } ?x } [ ?x ] }
        { T{ Add f ?x T{ Const f 0 } } [ ?x ] }
        { T{ Mul f ?x T{ Const f 1 } } [ ?x ] }
        { T{ Mul f T{ Const f 1 } ?x } [ ?x ] }
        { T{ Mul f ?x T{ Const f 0 } } [ T{ Const f 0 } ] }
        { T{ Mul f T{ Const f 0 } ?x } [ T{ Const f 0 } ] }
        { T{ Add f T{ Const f ?x } T{ Const f ?y } }
                                       [ ?x ?y + Const boa ] }
        { T{ Mul f T{ Const f ?x } T{ Const f ?y } }
                                       [ ?x ?y * Const boa ] }
        [ ]
    } match-cond ;

We have a way to recursively simplify some expressions:

: simplify ( expr -- expr' )
    {
        { T{ Add f ?x ?y } [ ?x ?y [ simplify ] bi@ Add boa ] }
        { T{ Mul f ?x ?y } [ ?x ?y [ simplify ] bi@ Mul boa ] }
        [ ]
    } match-cond simplify1 ;

Finally, we have a word that tries to simplify a value to a constant:

: simplify-value ( expr -- str )
    simplify {
        { T{ Const f ?x } [ ?x ] }
        [ drop "Could not be simplified to a Constant." ]
    } match-cond ;

To check that it works, we can write a unit test that simplifies the original expression above:

{ 15 } [
    T{ Add f
        T{ Mul f
            T{ Add f
                T{ Const f 1 }
                T{ Mul f
                    T{ Const f 0 }
                    T{ Var f "x" } } }
            T{ Const f 3 } }
        T{ Const f 12 } }
    simplify-value
] unit-test

That's cool, but wouldn't it be better if we could work on quotations directly? Let's make a word that converts a quotation to an expression:

: >expr ( quot -- expr )
    [
        {
            { [ dup string? ] [ '[ _ Var boa ] ] }
            { [ dup integer? ] [ '[ _ Const boa ] ] }
            { [ dup \ + = ] [ drop [ Add boa ] ] }
            { [ dup \ * = ] [ drop [ Mul boa ] ] }
        } cond
    ] map concat call( -- expr ) ;

Now that we have that, our test case is a lot simpler:

{ 15 } [
    [ "x" 0 * 1 + 3 * 12 + ] >expr simplify-value
] unit-test

The code for this is on my GitHub.

Note: this takes advantage of a small feature that I added to the match-cond word to provide a way to easily handle a fall-through pattern like the cond word.