Back to Dijkstra's_algorithm_(Inform_7)

## dijkstra.inform7

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3 (http://creativecommons.org/publicdomain/zero/1.0/).
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5 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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14 ]
15
16 "Dijkstra's Algorithm" by Dave
17
18 A node is a kind of thing.
19 Contact relates nodes to each other.
20 The verb to contact (he contacts, they contact, he contacted, it is contacted, he is contacting) implies the contact relation.
21 The current node is a node that varies.
22
23 A node can be found, examined, or unreached.
24 A node has a number called the total distance.
25 Definition: a node is near if its total distance is 10 or less.
26
27 Following relates various nodes to one node (called the precedent).
28 The verb to follow (he follows, they follow, he followed, it is followed, he is following) implies the following relation.
29 Every turn: run Dijkstra's algorithm.
30
31 To run Dijkstra's algorithm:
32 	initialize Dijkstra's algorithm from the current node;
33 	while some of the nodes are examined begin;
34 		continue Dijkstra's algorithm;
35 	end while.
36
37 To initialize Dijkstra's algorithm from (n - a node):
38 	clear the state;
39 	now n is examined;
40 	change the total distance of n to 0.
41
42 To continue Dijkstra's algorithm:
43 	let n be the nearest examined node;
44 	now n is found;
45 	repeat with m running through the nodes contacting n begin;
46 		examine m from n;
47 	end repeat.
48
49 To examine (m - a found node) from (n - a node): now m is found.
50
51 To examine (m - an unreached node) from (n - a node):
52 	now m is examined;
53 	change the total distance of m to the extension of n to m;
54 	now m follows n.
55
56 To examine (m - an examined node) from (n - a node):
57 	let d be the extension of n to m;
58 	if the total distance of m > d begin;
59 		change the total distance of m to d;
60 		now m follows n;
61 	end if.
62 To clear the state:
63 	repeat with m running through nodes begin;
64 		now m is unreached;
65 		now m does not follow anything;
66 	end repeat;
67
68 To decide what number is the extension of (n - a node) to (m - a node):
69 	decide on the total distance of n + the distance between m and n.
70 Barcelona, Geneve, Lausanne, London, Marseille, Narbonne, Oxford, Paris, and Toulouse are nodes.
71
72 Table of Intercity Distances
73 src	dst	distance
74 Barcelona	Narbonne	250
75 Geneve	Lausanne	64
76 Geneve	Marseille	260
77 Geneve	Narbonne	550
78 Geneve	Paris	540
79 Geneve	Toulouse	700
80 Lausanne	Paris	536
81 London	Oxford	95
82 London	Paris	440
83 Marseille	Narbonne	260
84 Narbonne	Toulouse	150
85 Paris	Toulouse	680
86
87 To decide what number is the distance between (n - a node) and (m - a node):
88 	repeat through the Table of Intercity Distances begin;
89 		if the src entry is n and the dst entry is m, decide on the distance entry;
90 		if the src entry is m and the dst entry is n, decide on the distance entry;
91 	end repeat.
92
93 Definition: a node is initial if it is the current node.
94 To slide the marker from (n - an initial node):
95 	say "You take the marker from [n] and slide it".
96 To slide the marker from (n - a node):
97 	slide the marker from the precedent of n;
98 	say " to [n]".
99 To slide the marker to (n - a node):
100 	slide the marker from the precedent of n;
101 	say ", winding up at [n].".
102
103 planning is an action applying to one visible thing.
104 understand "[a node]" as planning.
105 check planning:
106 	if the current node is the noun, say "The marker is already at [the current node]." instead.
107 carry out planning:
108 	slide the marker to the noun;
109 	change the current node to the noun.
110
111 The Map Room is a room.
112 "You are looking at a roadmap centered on the south of France[line break]Say 'relations' to examine the current graph state[line break]Say 'city name' to plan a trip from [the current node].".
113 The marker and the roadmap are scenery in the Map Room.
114
115 When play begins:
116 	repeat through the Table of Intercity Distances begin;
117 		now the src entry contacts the dst entry;
118 		now the dst entry contacts the src entry;
119 	end repeat;
120 	repeat with n running through the nodes begin;
121 		move n to the Map Room;
122 	end repeat;
123 	change the current node to Barcelona;
124 	run Dijkstra's algorithm.
125
126 Test me with "barcelona/lausanne/barcelona/paris/marseille"
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