Box the compass: Difference between revisions

=={{header|Prolog}}==

Part 1 : The following knowledge base takes a heading in degrees and returns the correct 32-point compass heading. It can also go in the other direction.

<lang prolog>

compassangle(1, 'North',n, 0.00).

compassangle(2, 'North by east', nbe, 11.25).

compassangle(3, 'North-northeast', nne,22.50).

compassangle(4, 'Northeast by north', nebn,33.75).

compassangle(5, 'Northeast', ne,45.00).

compassangle(6, 'Norteast by east', nebe,56.25).

compassangle(7, 'East-northeast', ene,67.50).

compassangle(8, 'East by North', ebn,78.75).

compassangle(9, 'East', e,90.00).

compassangle(10, 'East by south', ebs, 101.25).

compassangle(11, 'East-southeast', ese,112.50).

compassangle(12, 'Southeast by east', sebe, 123.75).

compassangle(13, 'Southeast', se, 135.00).

compassangle(14, 'Southeast by south', sebs, 146.25).

compassangle(15, 'South-southeast',sse, 157.50).

compassangle(16, 'South by east', sbe, 168.75).

compassangle(17, 'South', s, 180.00).

compassangle(18, 'South by west', sbw, 191.25).

compassangle(19, 'South-southwest', ssw, 202.50).

compassangle(20, 'Southwest by south', swbs, 213.75).

compassangle(21, 'Southwest', sw, 225.00).

compassangle(22, 'Southwest by west', swbw, 236.25).

compassangle(23, 'West-southwest', wsw, 247.50).

compassangle(24, 'West by south', wbs, 258.75).

compassangle(25, 'West', w, 270.00).

compassangle(26, 'West by north', wbn, 281.25).

compassangle(27, 'West-northwest', wnw, 292.50).

compassangle(28, 'Northwest by west', nwbw, 303.75).

compassangle(29, 'Northwest', nw, 315.00).

compassangle(30, 'Northwest by north', nwbn, 326.25).

compassangle(31, 'North-northwest', nnw, 337.50).

compassangle(32, 'North by west', nbw, 348.75).

compassangle(1, 'North', n, 360.00).

compassangle(Index , Name, Heading, Angle) :- nonvar(Angle), resolveindex(Angle, Index),

compassangle(Index,Name, Heading, _).

resolveindex(Angle, Index) :- N is Angle / 11.25 + 0.5, I is floor(N),Index is (I mod 32) + 1.

</lang>

Part 2 : The following rules print a table of indexes.

<lang prolog>

printTableRow(Angle) :- compassangle(Index, Name, _, Angle),

write(Index), write(' '),

write(Name), write(' '),

write(Angle).

printTable([X|Xs]) :- printTableRow(X), nl, printTable(Xs),!.

printTable([]).

</lang>

The following query prints the required table.

<lang prolog>

?- printTable([0.0, 16.87, 16.88, 33.75, 50.62, 50.63, 67.5, 84.37, 84.38, 101.25, 118.12, 118.13, 135.0, 151.87, 151.88, 168.75, 185.62,

185.63, 202.5, 219.37, 219.38, 236.25, 253.12, 253.13, 270.0, 286.87, 286.88, 303.75, 320.62, 320.63, 337.5, 354.37, 354.38]).

1 North 0.0

2 North by east 16.87

3 North-northeast 16.88

4 Northeast by north 33.75

5 Northeast 50.62

6 Norteast by east 50.63

7 East-northeast 67.5

8 East by North 84.37

9 East 84.38

10 East by south 101.25

11 East-southeast 118.12

12 Southeast by east 118.13

13 Southeast 135.0

14 Southeast by south 151.87

15 South-southeast 151.88

16 South by east 168.75

17 South 185.62

18 South by west 185.63

19 South-southwest 202.5

20 Southwest by south 219.37

21 Southwest 219.38

22 Southwest by west 236.25

23 West-southwest 253.12

24 West by south 253.13

25 West 270.0

26 West by north 286.87

27 West-northwest 286.88

28 Northwest by west 303.75

29 Northwest 320.62

30 Northwest by north 320.63

31 North-northwest 337.5

32 North by west 354.37

1 North 354.38

true.

</lang>