example: Add some examples for random functions and networks.

example/example.org

@@ -523,6 +523,59 @@ tab
    | #t | #t | #t | #t  | #f  | #f  |
    :END:
 
+** Random functions and networks
+   To avoid having different results every time a code block in this
+   section is run, every code block seeds the random number generator
+   to 0.
+
+ =dds/networks= can generate random functions, given a domain for
+   each of its arguments and for the function itself.  Consider the
+   following domains:
+   #+NAME: simple-domains
+   | a | (#f #t)    |
+   | b | (1 2)      |
+   | c | (cold hot) |
+
+   Here's a random function taking values in the codomain =(4 5 6)=:
+   #+BEGIN_SRC racket :results table drawer :var simple-domains=munch-sexp(simple-domains)
+(random-seed 0)
+(define rnd-func (random-function/state (unorg simple-domains) '(4 5 6)))
+(tabulate-state rnd-func (unorg simple-domains))
+   #+END_SRC
+
+   #+RESULTS:
+   :RESULTS:
+   | a  | b | c    | f |
+   | #f | 1 | cold | 4 |
+   | #f | 1 | hot  | 5 |
+   | #f | 2 | cold | 4 |
+   | #f | 2 | hot  | 4 |
+   | #t | 1 | cold | 5 |
+   | #t | 1 | hot  | 6 |
+   | #t | 2 | cold | 4 |
+   | #t | 2 | hot  | 5 |
+   :END:
+
+   We can build an entire random network over these domains:
+   #+BEGIN_SRC racket :results table drawer :var simple-domains=munch-sexp(simple-domains)
+(random-seed 0)
+(define n (random-network (unorg simple-domains)))
+(tabulate-network n (unorg simple-domains))
+   #+END_SRC
+
+   #+RESULTS:
+   :RESULTS:
+   | a  | b | c    | f-a | f-b | f-c  |
+   | #f | 1 | cold | #t  |   2 | cold |
+   | #f | 1 | hot  | #t  |   1 | cold |
+   | #f | 2 | cold | #f  |   1 | hot  |
+   | #f | 2 | hot  | #t  |   2 | hot  |
+   | #t | 1 | cold | #t  |   1 | cold |
+   | #t | 1 | hot  | #f  |   1 | hot  |
+   | #t | 2 | cold | #t  |   2 | cold |
+   | #t | 2 | hot  | #f  |   1 | hot  |
+   :END:
+
 
 * Reaction systems
   :PROPERTIES: