Editing Burton-style nondeterminism (section)

== Referential transparency? ==

Burton states how this technique preserves referential transparency on page 2:

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In practice these values will be determined at run time (when used as arguments to a special function ''choice''), but once fixed will never change.
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From this we can make two observations:

* The effects involved in determining a <code>Decision</code> value only occur once: when it is initially used;
    
* Once it has been determined, a <code>Decision</code> value won't change: it remains constant, even if reused.

When looked at in this way, Burton's technique has a striking resemblance to lazy evaluation:

* the evaluation of a thunk (suspended expression) only occurs when it is initially used;

* once its result has been determined, it won't change: it replaces the original thunk.

The practical difference between Burton's technique and lazy evaluation is that (some of) the effects involved in the former are ''visible'' outside functional programs which use <code>Decision</code> values.

[[Category:Code]]
[[Category:Nondeterminism]]

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