Archive for December, 2008
Merry Christmas
I wish you all a very merry christmas 
Hello Standard ML (of New Jersey)
Back when I was at the university we had a course called “Programming languages”, there we learned a little something about a lot of known and less known programming languages. One of these languages was Standard ML, and I remember that I was quite fascinated with that language, it was so different from everything else we had learned. Since then the functional languages have become a bit more common, with Erlang, F#, Clojure, Scala and Haskell as some examples (more functional languages can be found here: http://en.wikipedia.org/wiki/Category:Functional_languages). I have not used any functional languages since then and I thought I would just briefly refresh my memory by installing Standard ML and try the most basics of the language.
Installation
I am currently using a Mac so installing sml-nj was really simple. I downloaded the mac .dmg package from http://www.smlnj.org/ and ran the installer. the system was installed by default at /usr/local/smlnj-110.68. I added the path to my .profile file, which enables me to start sml without being in the sml bin root folder.
When that was done I could start the sml shell (just type sml in your shell):
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kristian-lundes-macbook-pro:sml kristianlunde$ sml
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Standard ML of New Jersey v110.68 [built: Thu Sep 4 16:23:20 2008]
Example 1: Start standard ML
(To exit the sml shell use key combination: CTRL + D).
First touch – Hello World
I always do a Hello World programming in a new language. Even though I have been playing around with Standard ML before I do not remember a hole lot of it, so I start from scratch.
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- "Hello World";
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val it = "Hello World" : string
Example 2: Print “Hello World”
The – is the sml prompt, to end a expression the semi-colon is used. So to write Hello World all you have to do is to apply quotes around the text and end it with ; and hit enter. The result gives us the text and the data type.
The first function
To do a Hello world proved to be quite simple, so lets take it a bit further and write a function which prints the hello world text.
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1. – fun hello ():string = "Hello World";
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2. val hello = fn : unit -> string
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3. – hello();
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4. val it = "Hello World" : string
Example 3: The first function
The function itself is a one liner seen on line 1 in the example above. The function is created using the fun keyword, the function is named hello and have no parameters which result in the (). The function return a result of the data type string, this is defined with the :string element, The content of the function start after the equal sign, and is just a print of the hello world text. To end the function close semi-colon.
When creating a function which is compiled we get the response seen in line 2. This tell us that hello is a function and that it return a string. I believe the unit text mean that the function does not take any parameters (I might be wrong).
To execute the function just type the name of the function, see line 3 in the example above, this result in printing out the “hello world” text as seen in line 4. Line 4 tell us that the result of the function is “Hello World” and the data type is a string.
Functions with parameters
Now we have created our first function, but a function usually need one or more parameters, so let us have a look at that. The next function is a simple echo function which just print the text to screen.
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1. – fun echo (s:string):string = s;
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2. val echo = fn : string -> string
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3. – echo("Hello World");
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4. val it = "Hello World" : string
Example 4: Function with parameter
Line 1 in example 4 define the function, it takes one parameter s as a string, the return data type is also a string and it just output the string to the shell. When the function is executed in line 3 the parameter is “Hello World” and the result is seen in line 4.
To add more than one parameter just add a comma between the parameters. Remember to define a data type on all the parameters.
Example 5 is a function which takes to parameters and sum the two parameters together before returning the result.
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1. – fun sum(x:int,y:int):int = x + y;
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2. val sum = fn : int * int -> int
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3. – sum(10,20);
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4. val it = 30 : int
Example 5: function with multiple parameters
Lambda expressions
Lambda expressions is also known as anonymous functions, and create a function without any name. This is used quite frequently in sml and are written as seen in example 6.
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fn() => print "Hello World";
Example 6: lambda expression.
The example 6 do not do much except print out the Hello world text when it is called. Naturally a lambda expression must be called as part of another function or code snippet.
Load a function from file
To load sml code from a file just use:
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- use "../sml/myfile.sml";
Where you replace ../sml/myfile.sml to point to your file.
Resources
This is the best online introductions I have found so far are:
www.pllab.riec.tohoku.ac.jp/smlsharp/smlIntroSlides.pdf
http://www.cs.cornell.edu/riccardo/prog-smlnj/notes-011001.pdf
A short FAQ:
http://www.smlnj.org//doc/FAQ/index.html
I really have not showed anything of the fancy stuff you could go about and build with Standard ML, but hopefully I am able to spend some more hours playing around with standard ML and write another blog post.
2.5 applications I really miss in OS X
In a previous post I wrote about my new life running on a MacBook Pro and OSX. It has now been over a month since I switch over to this unix hybrid, and I am quite liking it. It is very stable, I almost never turn off my mac, but I put it to sleep, this is working fine and my last reboot is over two weeks ago. I have also gotten used to some of the new weird keys on the keyboard and the shortcuts, but I am not yet as efficent on a mac as I am/were on ubuntu/windows. During the last few weeks I have discovered that Apple and other in most cases provide me with the applications I need, but not always, and here is the list of applications I really miss:
1. TortoiseSVN
Windows application which integrates itself with Windows Explorer and provide a SVN client. I would say that this is the best graphical SVN client I have ever used. SVNX which I currently use on the mac is not a very good replacement.
2. Kate / Notepad++
Kate is a KDE text editor for unix based systems. Notpad++ is Kates equivalent on Windows. Both editors provide a simple and intuitive user interface, and a lot of syntax highlight files for all the obscure programming languages you can think of.
I know Mac have the TextMate application, but that is third party software and you have to pay €48 or something for a license, and that is probably what I probably will do. The TextMate application is really good and provide most if not all the functionality that Kate and Notepad++ provide.
In my desperation for a good text editor I almost went off and tried to install KDE on Mac, but that was said to be experimental and could break my entire system. So that is a no go for now. The article however was really interesting:
URL: http://www.simplehelp.net/2007/07/22/how-to-install-kde-4-in-os-x/.
I still miss my ubuntu system and will probably go off and install parallels or vmware and ubuntu, just to have it accessible
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