1. Programming Style and Technique
Notes for Ch.8 of Bratko
For CSCE 580 Sp03
Marco Valtorta

2. Use of Recursion: maplist
maplist is an example of a “higher-order function”: a function that applies to another function
In the original LISP (McCarthy, 1960):
((label maplist
(lambda (x f)
(cond ((null x) ‘( ))
(‘t (cons (f (car x)) (maplist (cdr x) f))))))
Maplist( List, F, NewList) if NewList contains the result of applying F to each element of List, in order
The function F the binary relation representing the function we want to apply

3. maplist II Boundary (base) case: List = [ ]
if List = [ ] then NewList = [ ]
General case: List = [ X|Tail]
To transform a list of the form [ X|Tail], do
transform the item X by F, obtaining New X, and
transform the list Tail obtaining NewTail
the whole transformed list if [ NewX|NewTail]
See ch8_1.pl
renamed maplist1, because maplist is built in, with slightly different meaning
call/2 can be used for a more functional (less relational) style

4. Generalization Generalization allows us to use recursion
Example: eight queens
without generalization, no integer to recur on!
Define nqueens( Pos,N)
if N queens are safe in position Pos
Base case: N = 0: trivial
General case: N > 0
achieve a safe configuration of N-1 queens
add the remaining queen so that it does attack
eightqueens( Pos) :- nqueens( Pos,8).

5. Debugging
Most Prolog interpreters and compilers use a four-port model for goals
call
foo/n
succeed
fail
retry

6. Debugging Example ch3_1.pl1 [trace] 1 ?- del( a,[a,b,a],L)
See Section 2.9 of SWI-Prolog manual for some extensions

7. Improving Efficiency Eight queens, again: Map coloring
using a more informed initial ordering of queen coordinate values helps, as described in the comments at the end of ex4_6.pl
Map coloring
start with countries that have many neighbors
Warnsdorff’s heuristic for the knight’s tour

8. Difference Lists
concat( A1-Z1,Z1-Z2,A1-Z2).
See UseDefK4.ppt

9. Accumulators
sumlist
See UseDefK4.ppt