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Smalltalk Express does not come equipped with a random-number generator, but you can implement a simple random-number generator with the following, which is adapted from Smalltalk-80: The Language, by Adele Goldberg and David Robson (Addison-Wesley, 1989); it, in turn, is based on Lehmer's linear congruential method, described in The Art of Computer Programming: Fundamental Algorithms, Volume 1, by Donald Knuth (Addison-Wesley, 1968).
The random numbers vary uniformly from 0.0, exclusively, to 1.0
exclusively. The new: method takes an integer argument that
provides a starting point for the generation of random numbers, so that you
are not stuck with the same sequence of random numbers each time that you
create an instance of the Random class. The bitAnd:
method peforms bit-by-bit logic on integers:
Random class definition Object subclass: #Random instanceVariableNames: 'seed' classVariableNames: '' poolDictionaries: '' Random method definition • class new: arg ^ super new initialize: arg. Random method definition • instance initialize: x seed := x. Random method definition • instance next | handle | [seed := 13849 + (27181 * seed) bitAnd: 65535. handle := seed / 65536.0. handle = 0] whileTrue: []. ^ handle.
Now, using an instance of the Random class assigned to
Generator, a global variable, you define a method,
deliveryInterval that produces random numbers distributed between
0.75 and 1.25.