Commit f250d33709ace2d5cd1e271c71f509a2f05f4d03 - ALPACA

Explain classes more, begin introducing neighbourhoods. catseye 12 years ago

1 changed file(s) with 92 addition(s) and 19 deletion(s). Raw diff Collapse all Expand all

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doc/ALPACA.markdown less more

6	6
7	7	The language described herein is mostly compatible with the version
8	8	of language which has existed until now (version 0.9x). However, it
9		extends it in some significant ways, and it may be backwards-incompatible
10		in certain way. An implementation of 1.0-PRE does not yet exist.
	9	extends it in some significant ways, and is be backwards-incompatible
	10	in certain minor ways. An implementation of 1.0-PRE does not yet exist.
11	11
12	12	Encoding
13	13	--------

22	22	An ALPACA description consists of a list of one or more _definitions_,
23	23	optionally followed by an _initial configuration_.
24	24
25		Each definition may specify either a _state_ or a _class_. The definitions
26		in the list are seperated with semicolons and the list ends with either a
27		period (if no initial configuration is given) or the token `begin` (which
28		introduces the initial configuration.)
	25	Each definition may specify either a _state_, a _class_, or a _neighbourhood_.
	26	The definitions in the list are seperated with semicolons and the list ends
	27	with either a period (if no initial configuration is given) or the token
	28	`begin` (which introduces the initial configuration.)
29	29
30	30	Example: a trivial ALPACA description with two states:
31	31

41	41
42	42	#### Representation Declarations ####
43	43
44		Each representation declaration may be a single ASCII character enclosed in
45		quotes, or it may be a datum tagged with a name. The tag declares the
46		purpose and/or the intended interpretation of the datum. The tag may be
	44	Each representation declaration may be a single printable ASCII character
	45	enclosed in quotes, or it may be a datum tagged with a name. The tag declares
	46	the purpose and/or the intended interpretation of the datum. The tag may be
47	47	drawn from a set defined by this specification, or it may be
48	48	implementation-defined. The datum may consist essentially arbitrary data,
49	49	and may refer to a character, a colour, a graphic image, or anything else.

93	93	to Thing when true;
94	94	state Thing
95	95	to Space when true.
	96
	97	TODO default transition rule.
96	98
97	99	##### State Referents #####
98	100

180	182	of a state referent, the second term is a class referent. An example will
181	183	be given under "Classes", below.
182	184
183		An adjacency comparison is an expression consisting of an integer from
184		1 to 8 followed by a state or class referent. It evaluates to true
185		only if the cell has at least that many (Moore?) neighbours of that
186		state or class. (TODO: extend to other neighbourhoods.)
	185	An adjacency comparison is an expression consisting of an integer greater
	186	than or equal to 1, followed by an optional neighbourhood specifier,
	187	followed by a state or class referent. It evaluates to true only if the
	188	cell has at least that many neighbours of that state or class, in that
	189	neighbourhood. If no neighbourhood is given, a Moore neighbourhood is
	190	assumed.
187	191
188	192	### Classes ###
189	193
190	194	A class declaration defines the general behaviour of a number of states.
191		Each state can belong to many classes, and are listed in overload order.
192		Classes can have their own rules, and the `is` operator can be used to
193		check for any of the states of a class instead of a single state.
	195	Classes can have their own rules, and these are shared by all states which
	196	are members of the class.
	197
	198	Example: a cellular automaton with three states, two of which are members
	199	of the same class.
	200
	201	state " " Space
	202	to Space when true;
	203	class Animal
	204	to Space when > Space;
	205	state "*" Dog is Animal
	206	to Cat when ^ Cat;
	207	state "#" Cat is Animal
	208	to Dog when ^ Dog.
	209
	210	Each state can belong to zero or more classes. When it belongs to more
	211	than one, class the transition rules for each class are applied in order
	212	the classes are listed in the state definition.
	213
	214	(TODO: Do the rules in a state take precedence over rules inherited from the
	215	class? May need to fix next example.)
	216
	217	Example: a cellular automaton with two states and two classes, where both
	218	states are members of both classes, but they inherit in different orders.
	219	In it, Ones always remain Ones, and Twos always remain Twos.
	220
	221	class AlphaType
	222	to One when true;
	223	class BetaType
	224	to Two when true;
	225	state "1" One is AlphaType is BetaType
	226	to Two when true;
	227	state "2" Two is BetaType is AlphaType
	228	to One when true.
	229
	230	In a transition rule, a class-inclusion comparison may be used by
	231	giving a state referent, the token `is`, and the name of a class.
	232	Intuitively, this evaluates to true if the state so referred to is a
	233	member of that class.
	234
	235	Example: (TODO describe)
	236
	237	state " " Space
	238	to Space when true;
	239	class Animal
	240	to Space when > is Animal;
	241	state "*" Dog is Animal
	242	to Cat when not ^ is Animal;
	243	state "#" Cat is Animal
	244	to Dog when not ^ is Animal.
	245
	246	### Neighbourhoods ###
	247
	248	Example:
	249
	250	neighbourhood Moore
	251	(< > ^ v ^> ^< v> v<);
	252	state " " Space
	253	to Active when 1 Moore Active;
	254	state "*" Active
	255	to Space when 4 (^ v < >) Space.
194	256
195	257	### Initial Configuration ###
196	258

211	273
212	274	AlpacaProgram ::= Entries ("." \| "begin" initial-configuration).
213	275	Entries ::= Entry {";" Entry}.
214		Entry ::= Class \| State.
215		Class ::= "class" ClassID {MembershipDecl}
	276	Entry ::= ClassDefinition
	277	\| StateDefinition
	278	\| NeighbourhdDef.
	279	ClassDefinition ::= "class" ClassID {MembershipDecl}
216	280	[Rules].
217		State ::= "state" StateID {ReprDecl} {MembershipDecl}
	281	StateDefinition ::= "state" StateID {ReprDecl} {MembershipDecl}
218	282	[Rules].
	283	NeighbourhdDef ::= "neighbourhood" NeighbourhoodID
	284	Neighbourhood.
219	285
220	286	ClassID ::= identifier.
221	287	StateID ::= identifier.
	288	NeighbourhoodID ::= identifier.
222	289	ReprDecl ::= quoted-char
223	290	\| identifier ":" quoted-string.
224	291

240	307	\| RelationalFunc.
241	308	RelationalFunc ::= StateReferent (["="] StateReferent \| ClassReferent).
242	309	AdjacencyFunc ::= ("1" \| "2" \| "3" \| "4" \| "5" \| "6" \| "7" \| "8")
	310	[Neigbourhood \| NeighbourhoodID]
243	311	(StateReferent \| ClassReferent).
244	312	BoolPrimitive ::= "true" \| "false" \| "guess".
	313
	314	Neighbourhood ::= "(" {arrow-chain} ")".
245	315
246	316	The following are token definitions, not productions.
247	317

298	368	This is no longer supported. However, a future version might introduce a
299	369	more "readable" alternative state referent syntax.
300	370
	371	Previous versions of ALPACA always assumed a Moore neighbourhood when making
	372	an adjacency comparison.
	373
301	374	Previous versions of ALPACA did not support giving an initial configuration
302	375	for the cellular automaton.