Magik Tricks

Smallworld Magik is an object oriented language, so almost everything you deal with is an object.  Some examples of objects:

• Integers (1, 13, 2008)
• Floating point (1.0, 3.1415, 2e3, 0.57721)
• Note: the e in 2e6 is 2x10^6, not 2*e^6 where e = Natural Logarithmic Base
• Note: 0.57721 works while .57721 will fail
• Character( %c, %l, %t)
• Note the % denotes a character object

There are a few special objects as well.  The keywords _unset, _true, _false, and _maybe are all objects and can be treated as such.

The string “It’s the end of the world as we know it.” is actually an array of characters.  Knowing this, we can treat it as a collection without having to parse the string.  As objects, they can be compared with each other.  This code returns the string in alphabetical order, with weight given to punctuation, and capitalization first.  This is accomplished through Magik’s _cf comparison which evaluates characters based on their ASCII values. 

Or reversed:

We create an empty string “” and append to it the result of the as_simple_vector method on the sorted collection we created from our string.  Simplicity defined.

In the next example we create a string object and assign it to tmp1.  We then assign the tmp1 to tmp2.  In this case tmp1 and tmp2 don’t just have the same value, they are the same object.

This would not be true in the next case.  Both tmp1 and tmp2 are assigned the same value, but they are not the same object. 

Final notes on the subject of objects:

• Variable assignment doesn’t copy, it references. 
• Variable assignment is NOT strongly typed so you don’t need to declare it first, just assign a variable to an object, be it a number, a string, an array, a collection, or even a running application.

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Assigning variables in Smallworld Magik can be accomplished with a simple construct known as the left chevron (<<).  A simple variable assignment will look like this:

This expression states that the variable “a” becomes 10.  More complicated expressions can also be expressed in this way.

or

Variables may be named almost anything you want, with the following constraints:

• Start with a-z, or !
• Contain a-z, 0-9, _, ?, !
• Unlimited length
• Case independent (sorry camelCase junkies)

Variables may also be assigned in serial or parallel.  A series assignment might look like this:

Parallel variable assignment might look like this:

(s,c) << theta.sincos()  <--this works because sincos() returns two values, sin and cos

There is a somewhat classic programmer problem for swapping two variables without using a temp variable.  One of the many solutions being as follows:

Smallworld Magik has a more elegant solution however, using a swapping assignment.

Variable can be assigned inside other structures as well.  A common use for this is to assign a variable during an if-then evaluation.

There are other variations to the left chevron that have their uses.

a +<< 1 will increment a by 1.

a -<< 1 will de-increment a by 1.

a *<< 2 will multiply a by 2.

a /<< 2 will divide a by 2.

A seldom used, but kind of interesting one is known as the boot assignment.

This is the same as saying a << b followed by b << 10.  Essentially b becomes 10 and returns its original value which is in turn assigned to a.

One final note on Smallworld Magik variables is that developers tend to use longer names to describe most variables separated by an underscore (_) with the exception being when it is an iterated variable inside of a loop.  The variable ‘e’ is used by many to indicate an element inside of a loop, while more permanent element references would be named an_element.

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It is customary to declare your intention to learn the language by creating the “Hello World” program.   The simplest way to do this in Magik is to type write(“Hello World!”) at the command line.

This works because Magik compiles code on the fly and executes them instantly from the command line.   This is great for a lot of stuff, but it doesn’t qualify as having coded our first program, so we need to find a new place to write code that doesn’t compile instantly.  The best place for this is the scratch buffer.

To get to the scratch buffer press <ctrl>-x, b to bring up the “switch to buffer:” command on the very bottom of your emacs screen.  Type *scratch* and hit enter and the scratch buffer will appear.  In most cases typing *s followed by a tab should auto-complete the line for you, unless you have another buffer that starts with *s.  Most people don’t.

The following text is populated in the scratch buffer the first time you enter it.

This buffer is for notes you don't want to save, and for Lisp evaluation.
If you want to create a file, visit that file with C-x C-f,
then enter the text in that file's own buffer.

This needs to be deleted before you can utilize the buffer.  Once the buffer is empty you can begin writing a program.  At the moment it is a plain text buffer, but we can fix that.  Pressing <alt-x> and typing magik-mode will enable Magik mode in the buffer.  This allows Magik specific functions like auto complete, keyword recognition, and word coloring to work.

To write our first program we will use one of the simplest constructs available, a procedure or a proc.

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