val page 9 - Dave's Blog

Tab Expansion in PowerShell

PowerShell gives us a real CLI for Windows based around .Net stuff. I don't like the creation of a new shell language but I suppose it makes sense given that they want something C# like but not C# exactly since that's much to verbose and strict for a CLI. One of the functions you can override is the TabExpansion function which is used when you tab complete commands. I really like this and so I've added on to the standard implementation to support replacing a variable name with its value, tab completion of available commands, previous command history, and drive names (there not restricted to just one letter in PS).

Learning the new language was a bit of a chore but MSDN helped. A couple of things to note, a statement that has a return value that you don't do anything with is implicitly the return value for the current function. That's why there's no explicit return's in my TabExpansion function. Also, if you're TabExpansion function fails or returns nothing then the builtin TabExpansion function runs which does just filenames. This is why you can see that the standard TabExpansion function doesn't handle normal filenames: it does extra stuff (like method and property completion on variables that represent .Net objects) but if there's no fancy extra stuff to be done it lets the builtin one take a crack.

Here's my TabExpansion function. Probably has bugs, so watch out!

function EscapePath([string] $path, [string] $original)
{
    if ($path.Contains(' ') -and !$original.Contains(' '))
    {
        '"'   $path   '"';
    }
    else
    {
        $path;
    }
}

function PathRelativeTo($pathDest, $pathCurrent)
{
    if ($pathDest.PSParentPath.ToString().EndsWith($pathCurrent.Path))
    {
        '.\'   $pathDest.name;
    }
    else
    {
        $pathDest.FullName;
    }
}

#  This is the default function to use for tab expansion. It handles simple
# member expansion on variables, variable name expansion and parameter completion
# on commands. It doesn't understand strings so strings containing ; | ( or { may
# cause expansion to fail.

function TabExpansion($line, $lastWord)
{
    switch -regex ($lastWord)
    {
         # Handle property and method expansion...
         '(^.*)(\$(\w|\.) )\.(\w*)$' {
             $method = [Management.Automation.PSMemberTypes] `
                 'Method,CodeMethod,ScriptMethod,ParameterizedProperty'
             $base = $matches[1]
             $expression = $matches[2]
             Invoke-Expression ('$val='   $expression)
             $pat = $matches[4]   '*'
             Get-Member -inputobject $val $pat | sort membertype,name |
                 where { $_.name -notmatch '^[gs]et_'} |
                 foreach {
                     if ($_.MemberType -band $method)
                     {
                         # Return a method...
                         $base   $expression   '.'   $_.name   '('
                     }
                     else {
                         # Return a property...
                         $base   $expression   '.'   $_.name
                     }
                 }
             break;
          }

         # Handle variable name expansion...
         '(^.*\$)([\w\:]*)$' {
             $prefix = $matches[1]
             $varName = $matches[2]
             foreach ($v in Get-Childitem ('variable:'   $varName   '*'))
             {
                 if ($v.name -eq $varName)
                 {
                     $v.value
                 }
                 else
                 {
                    $prefix   $v.name
                 }
             }
             break;
         }

         # Do completion on parameters...
         '^-([\w0-9]*)' {
             $pat = $matches[1]   '*'

             # extract the command name from the string
             # first split the string into statements and pipeline elements
             # This doesn't handle strings however.
             $cmdlet = [regex]::Split($line, '[|;]')[-1]

             #  Extract the trailing unclosed block e.g. ls | foreach { cp
             if ($cmdlet -match '\{([^\{\}]*)$')
             {
                 $cmdlet = $matches[1]
             }

             # Extract the longest unclosed parenthetical expression...
             if ($cmdlet -match '\(([^()]*)$')
             {
                 $cmdlet = $matches[1]
             }

             # take the first space separated token of the remaining string
             # as the command to look up. Trim any leading or trailing spaces
             # so you don't get leading empty elements.
             $cmdlet = $cmdlet.Trim().Split()[0]

             # now get the info object for it...
             $cmdlet = @(Get-Command -type 'cmdlet,alias' $cmdlet)[0]

             # loop resolving aliases...
             while ($cmdlet.CommandType -eq 'alias') {
                 $cmdlet = @(Get-Command -type 'cmdlet,alias' $cmdlet.Definition)[0]
             }

             # expand the parameter sets and emit the matching elements
             foreach ($n in $cmdlet.ParameterSets | Select-Object -expand parameters)
             {
                 $n = $n.name
                 if ($n -like $pat) { '-'   $n }
             }
             break;
         }

         default {
             $varNameStar = $lastWord   '*';

             foreach ($n in @(Get-Childitem $varNameStar))
             {
                 $name = PathRelativeTo ($n) ($PWD);

                 if ($n.PSIsContainer)
                 {
                     EscapePath ($name   '\') ($lastWord);
                 }
                 else
                 {
                     EscapePath ($name) ($lastWord);
                 }
             }

             if (!$varNameStar.Contains('\'))
             {
                foreach ($n in @(Get-Command $varNameStar))
                {
                    if ($n.CommandType.ToString().Equals('Application'))
                    {
                       foreach ($ext in @((cat Env:PathExt).Split(';')))
                       {
                          if ($n.Path.ToString().ToLower().EndsWith(($ext).ToString().ToLower()))
                          {
                              EscapePath($n.Path) ($lastWord);
                          }
                       }
                    }
                    else
                    {
                        EscapePath($n.Name) ($lastWord);
                    }
                }

                foreach ($n in @(Get-psdrive $varNameStar))
                {
                    EscapePath($n.name   ":") ($lastWord);
                }
             }

             foreach ($n in @(Get-History))
             {
                 if ($n.CommandLine.StartsWith($line) -and $n.CommandLine -ne $line)
                 {
                     $lastWord   $n.CommandLine.Substring($line.Length);
                 }
             }

             # Add the original string to the end of the expansion list.
             $lastWord;

             break;
         }
    }
}

Investigation of a Few Application Protocols (Updated)

Windows allows for application protocols in which, through the registry, you specify a URL scheme and a command line to have that URL passed to your application. Its an easy way to hook a webbrowser up to your application. Anyone can read the doc above and then walk through the registry and pick out the application protocols but just from that info you can't tell what the application expects these URLs to look like. I did a bit of research on some of the application protocols I've seen which is listed below. Good places to look for information on URI schemes: Wikipedia URI scheme, and ESW Wiki UriSchemes.

Cadbury Bunny Sneaks Mint

	Cadbury Bunny Sneaks Mint Cadbury the bunny takes a moment from hiding under the chair to eat some mint. She comes out just to grab some mint and then goes back under the chair repeatedly for two minutes.	From: David Risney Views: 328 1 ratings
	Time: 02:01	More in Pets & Animals

Weekend Dinners: Old friends, Old library

Last Thursday I saw a bunch of college friends that I hadn't seen in a while, despite all of us working at Microsoft, and Saul and Ciera who were visiting. We had dinner at Typhoon! which I haven't been to in quite a while. Daniil and Val brought their cute child. I got to see Charlie and Matt who I'm not sure I've seen since my 25th birthday. There was much nerdiness. I need to remember to organize such a night myself sometime in near future so I don't have to wait another year to see them.

On the weekend Sarah and I went out to dinner at Carnegie's, a former public library in Ballard, Seattle that's now a restaurant. I saw the restaurant's website in Matt's delicious links and thought it looked interesting. The exterior and entryway look like a public library, but just inside its redone as a sort of modern version of french classical with a bar and two dining rooms. No pictures since my replacement camera only arrived today, but there are photos available. They serve french cuisine which was good and not as expensive as I would have expected. An interesting place, although its a bit of a drive and I'm not sure if we'll be going back soon.

Cadbury Hits Fireplace Shovel

	Cadbury Hits Fireplace Shovel Cadbury jumps out of her toy box hitting the fireplace shovel, and does a few other cute things.	From: David Risney Views: 76 1 ratings
	Time: 00:44	More in Pets & Animals

Cadbury Nibbles Toy Box

	Cadbury Nibbles Toy Box Cadbury sits in and eats her box of toys. She enjoys eating her toy box more often than playing with any of the toys.	From: David Risney Views: 343 2 ratings
	Time: 00:16	More in Pets & Animals

Tag Metadata in Feeds

As noted previously, my page consists of the aggregation of my various feeds and in working on that code recently it was again brought to my attention that everyone has different ways of representing tag metadata in feeds. I made up a list of how my various feed sources represent tags and list that data here so that it might help others in the future.

Update 2009-9-14: Added WordPress to the Tag Markup table and namespaces to the Tag Markup Scheme table.

Deriving a Non-Recursive Fibonacci Function Using Linear Algebra

In my Intro to Algorithms course in college the Fibonacci sequence was used as the example algorithm to which various types of algorithm creation methods were applied. As the course went on we made better and better performing algorithms to find the nth Fibonacci number. In another course we were told about a matrix that when multiplied successively produced Fibonacci numbers. In my linear algebra courses I realized I could diagonalize the matrix to find a non-recursive Fibonacci function. To my surprise this worked and I found a function.

Looking online I found that of course this same function was already well known. Mostly I was irritated that after all the algorithms we created for faster and faster Fibonacci functions we were never told about a constant time function like this.

I recently found my paper depicting this and thought it would be a good thing to use to try out MathML, a markup language for displaying math. I went to the MathML implementations page and installed a plugin for IE to display MathML and then began writing up my paper in MathML. I wrote the MathML by hand and must say that's not how its intended to be created. The language is very verbose and it took me a long time to get the page of equations transcribed.

MathML has presentation elements and content elements that can be used separately or together. I stuck to content elements and while it looked great in IE with my extension when I tried it in FireFox which has builtin MathML support it didn't render. As it turns out FireFox doesn't support MathML content elements. I had already finished creating this page by hand and wasn't about to switch to content elements. Also, in order to get IE to render a MathML document, the document needs directives at the top for specific IE extensions which is a pain. Thankfully, the W3C has a MathML cross platform stylesheet. You just include this XSL at the top of your XHTML page and it turns content elements into appropriate presentation elements, and inserts all the known IE extension goo required for you. So now my page can look lovely and all the ickiness to get it to render is contained in the W3C's XSL.

Kirkland Uncorked Weekend

Saturday we went to Kirkland Uncorked, a wine tasting festival near our home. We took the bus and after finding the correct one (they really should have different numbers for buses that are on the same route but traveling in different directions) made it to the festival. Unfortunately I don't remember any of the names of the wines just which ones I enjoyed by order. Recalling that I enjoyed the first one I had and the second to last one, doesn't really help me find them again. There were local artists who had setup booths and Sarah got a lovely necklace. After that we ate at Cactus which, because it was such a lovely day, had all its windows and doors open.

Sunday was quieter. A few household chores and plenty of GTA4. I almost got the One Man Army achievement but I found that after four minutes with six stars I eventually dropped back down to three stars without realizing it.

Generating N-D Tetris Pieces

When I woke up this morning for some reason I was thinking about Polytope Tetris, my N-D Tetris game, and specifically generating Tetris pieces in various number of dimensions. When I first wrote PTT I thought that as the number of dimensions increased you could end up with an infinite number of non-equivalent crazy Tetris pieces. However this morning I realized that because you only get four blocks per piece there are only a possible three joints in a single Tetris piece which means that you only need three dimensions to represent all possible distinct N-D Tetris pieces.

Below is the table of the various possible pieces per number of dimensions and sorted by the number of joints in the piece. Notice that the 'J' and 'L' become equivalent in 3D because you can rotate the 'J' through the third dimension to make it an 'L'. The same happens for 'S' and 'Z' in 3D, and 'S+' and 'Z+' in 4D.

Joints	Name	1D	2D	3D	+
1	I
2	J
	L
3	O
	T
	S
	Z
	T+
	S+
	Z+
	Total	1	7	8	7

As a consequence of not realizing there's a finite and small number of N-D Tetris pieces, I wrote code that would randomly generate pieces for a specified number of dimensions by wandering through Tetris space. This consists of first marking the current spot, then randomly picking a direction (a dimension and either forward or backward), going in that direction until hitting a previously unvisited spot and repeating until four spots are marked, forming a Tetris piece. However this morning I realized that continuing in the same direction until reaching am unvisited spot means I can't generate the 'T+' piece. I think the better way to go is keep the list of all possible pieces, pick one randomly, and rotate it randomly through the available dimensions. Doing this will also allow me to give distinct pieces their own specific color (like the classic Tetris games do) rather than picking the color randomly like I do now.