The implementation, unlike other Smalltalk environments, uses text files for program input and interprets the contents as Smalltalk code. In this way, GNU Smalltalk acts more like an interpreter rather than an environment in the traditional Smalltalk manner.
Iterating over enumerations and arrays using blocks:
A method such as inject:into: can accept both a parameter and a block. It iterates over each member of a list, performing some function on while retaining an aggregate. This is analogous to the foldl function in functional programming languages. For example:
On the first pass, the block receives 10 (the argument to inject) as sum, and 1 (the first element of the array) as element, This returns 11. 11 then becomes sum on the next pass, which is added to 3 to get 14. 14 is then added to 5, to finally return 19.
Blocks work with many built-in methods:
Using an enumeration and a block to square the numbers 1 to 10:
The following code defines a class named Person. By deriving from Magnitude, it automatically defines all comparison methods except one (<). With the addition of that one, asSortedCollection can sort by age. Note that we can override the way the object is printed/displayed (the default is to share the programmer-print and user-display representation) by overriding printOn:.
The above prints three names in reverse age order:
An exception is raised with a halt call:
An optional message can be added to the exception; there's also error: which raises a different kind of exception:
These are actually wrappers for the actual exception raising method, signal>:
Exceptions are handled by on:do: blocks.
Of course you can catch only particular exceptions (and their subclasses):
It is possible to use the exception object, which is made available to the handler clause, to exit or resume the first block: