Photo Fusing in Windows Live Photo Gallery

On my camera, I can make the self timer take 8 photos 2 seconds apart. This leaves me with a 1 in 8  chance of getting a good picture. However, using the photo fuse tool in Windows Live Photogallery, I can do a visual merge of the photos to pick my favorite part of each photo.  For example, I used the following source photos:

To created this composite photo, (To which I also applied straiten and auto fix)

That’s seriously cool!

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PowerShell: Tab Complete History

If you haven’t tried PowerTab or haven’t tried PowerTab recently stop, and check it out .  PowerTab makes powershell a real pleasure to use, and might be the feature that gets me over the powershell dip.

Once you’ve installed PowerTab , you can history complete by starting your command with a #, typing some letters and then hitting tab. For example:

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Batch to Powershell: Title

If you try to set the title of the window in powershell, 'title' won't work; but you can set the title using the $host object

 PS C:\> $Host.UI.RawUI.WindowTitle = "Donkey" 

You can also mess with other fun things like colors eg:

PS C:\>  $Host.UI.RawUI.BackgroundColor = [ConsoleColor]::Red 

If you're a big title user and have title burned into your muscle memory you can always create function called title e.g.:

 PS C:\Temp> function title ($t) {$host.UI.RawUI.WindowTitle=$t }
PS C:\Temp> title Donkey2 

Have fun moving into powershell.

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Powershell: Returning ScriptBlocks and Closures

Powershell lets you return scriptblocks (aka anonymous functions) from functions, for example:

function generateAdder ($n)
{
    {
        param ($x)
        $n+$x
    }
}

 
PS C:\> $add4 = generateAdder 4
PS C:\> & $add4 7
7

If you've used languages with closures you'd have expected to get back a function that adds 4 to a passed in value. You'd expect that because $n=4 was in lexical scope when we created the scriptblock to be returned. Recall powershell is dynamically scoped so we don't need to bind ($n) to a lexcial location, instead we can pick up $n from our current environment:

PS C:\> $n = "Hello"
PS C:\> & $add4 7
Hello7

What if you want to instantiate a closure with powershell instead? Luckily someone thought of that and you can do:

function generateAdder2 ($n)
{
    {
        param ($x)
        $n+$x
    }.GetNewClosure()
}

PS C:\> $add4 = generateAdder2 4
PS C:\> & $add4 7
11

Leave a comment if you use these features, I’m curious what you’d use them for.

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Batch to Powershell: dir /s

I often go looking for a file in batch, aka

c:\Program Files (x86)>dir /s fsi*
     Volume in drive C has no label.
     Volume Serial Number is 8EDE-D64E

     Directory of c:\Program Files (x86)\Microsoft F#\v4.0

    03/19/2010  02:02 PM           230,216 Fsi.exe
    09/30/2009  08:08 PM               158 Fsi.exe.config
                   2 File(s)        230,374 bytes

Unfortunately this doesn't 'just work' in powershell. A quick search on the internet shows in powershell 'dir /s' becomes 'dir -r', but the following doesn't work either:

PS C:\Program Files (x86)> dir -r fsi*
PS C:\Program Files (x86)>

What's going on? Let's check the help:

PS C:\Program Files (x86)> help dir

NAME
    Get-ChildItem

SYNOPSIS
    Gets the items and child items in one or more specified locations.


SYNTAX
    Get-ChildItem [[-Path] ] [[-Filter] ] [-Exclude ] [-For
    ce] [-Include ] [-Name] [-Recurse] [-UseTransaction] []

    Get-ChildItem [-LiteralPath]  [[-Filter] ] [-Exclude ]
    [-Force] [-Include ] [-Name] [-Recurse] [-UseTransaction] []

Ahh, path and filter are two separate arguments in powershell. This means we get 2 choices.

A) Pass a path to the dir command (pass ‘.’ for current directory):

PS C:\Program Files (x86)> dir . fsi* -r

    Directory: C:\Program Files (x86)\Microsoft F#\v4.0


Mode                LastWriteTime     Length Name
----                -------------     ------ ----
-a---         3/19/2010   2:02 PM     230216 Fsi.exe
-a---         9/30/2009   8:08 PM        158 Fsi.exe.config
PS C:\Program Files (x86)>

B) Explicitly pass the -filter argument name (which we can abbreviate to -fi)

PS C:\Program Files (x86)> dir -r -fi fsi*


    Directory: C:\Program Files (x86)\Microsoft F#\v4.0


Mode                LastWriteTime     Length Name
----                -------------     ------ ----
-a---         3/19/2010   2:02 PM     230216 Fsi.exe
-a---         9/30/2009   8:08 PM        158 Fsi.exe.config    
PS C:\Program Files (x86)>

OK you’re thinking who cares, I can still do dir /s faster in batch? Ah, but you can’t do this:

 PS C:\Program Files (x86)> dir -r -fi fsi* | Where-Object {$_.Length -gt 200KB}


    Directory: C:\Program Files (x86)\Microsoft F#\v4.0


Mode                LastWriteTime     Length Name
----                -------------     ------ ----
-a---         3/19/2010   2:02 PM     230216 Fsi.exe
PS C:\Program Files (x86)>

Have fun, and remember read the docs when things don’t work as you’d expecxt:)

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F# Tricks: Concise BoolToInt

As a C# programmer, you'd probably write BoolToInt as follows in F#:

	let boolToInt3 b = 
	   if b = true then 
		1
	   elif b = false
		0

Not a big win over C# yet, but a few things to point out about the concise syntax: Indentation implies blocks. There is no 'return' keyword. This function is statically typed, you don't see types since the compiler infers the types.

As a novice F# programmer a trick you learn is pattern matching. Pattern matching is like a case statement, but it's an expression and it's really powerful. I'll go into more details on pattern matching in future posts. For now, notice the elegance of the below:

	let boolToInt2 b = 
	    match b with 
		| true -> 1 
		| false -> 0 

Pattern matching is so useful to F# there is a syntax for creating a function of one parameter that only pattern matches, using that syntax, we define boolToInt in the final form of:

	let boolToInt3 = function 
	    | true -> 1 
	    | false -> 0 

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F# Tricks: Collecting Some Optional Values

Skip this post if you have no idea what F# is, and think LINQ is stupid.

When you map inputs to outputs with a function that can return None, or Some Output, you get an annoying issue of having a list containing Nones, and Some

s. For example:

// Contains both encrypted and un-encrypted files: 
let listOfFiles:Seq

// Return a decrypted File, or None if the file can't be decrypted.
let decryptFile file
 match file with
 | isFileDecryptable file -> Some DecryptFile file
 | _ -> None

// decryptedFiles contains Nones, intertwined with some Some  DecryptedFiles
let decryptedFiles = listOfFiles |> Seq.map decryptFile

Here are two ways to remedy that:

// To get a list of only decrypted files you could do:
let realDecryptedFiles = decryptedFiles |> Seq.filter Option.isSome |> Seq.map Option.get

// However, I prefer the more concise version of: 
let realDecryptedFiles = decryptedFiles |> Seq.collect   Option.toList

If you're an F# guru I'd love to hear your thoughts on this.

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