96 lines
2.7 KiB
Perl
96 lines
2.7 KiB
Perl
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% Utility Predicates
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% The following predicates are used in the puzzle solutions.
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% unique_solution( +Goal ) holds when Goal has one ground solution. Operationally,
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% Goal may produce several solutions, ("don't care" non-deterministically), but they
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% must all be identical (==).
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unique_solution( Goal ) :-
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findall( Goal, Goal, [Solution|Solutions] ),
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same_solution( Solutions, Solution ),
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Solution = Goal.
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same_solution( [], _Solution ).
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same_solution( [Solution0|Solutions], Solution ) :-
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Solution0 == Solution,
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same_solution( Solutions, Solution ).
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% forall( +Enumerator, +Test ) is true if Enumerator and Test are goals and Test holds everywhere
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% that Enumerator does. NB: does not further instantiate arguments.
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%% forall( Enumerator, Test ) :-
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%% \+ (call(Enumerator), \+ call(Test)).
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% member( ?Element, ?List ) holds when Element is a member of List.
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member( H, [H|_] ).
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member( H, [_|T] ):-
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member( H, T ).
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% select( ?Element, ?List0, ?List1 ) is true if List1 is equal to List1 with Element removed.
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select( H, [H|T], T ).
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select( Element, [H|T0], [H|T1] ):-
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select( Element, T0, T1 ).
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% memberchk( +Element, +List ) succeeds (once) if Element is a member of List.
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memberchk( Element, List ):-
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member( Element, List ),
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!.
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% between( +Lower, +Upper, ?Index ) is true if Lower =< Index =< Upper. Two valid cases are
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% possible:
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% - Index is already instantiated to an integer so the checks on order are applied (test).
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% - Index is a logical variable so a series of alternative solutions is generated as the
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% monotonic sequence of values between Lower and Upper (non-deterministic generator).
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%% between( Lower, Upper, Index ):-
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%% integer( Lower ),
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%% integer( Upper ),
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%% Lower =< Upper,
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%% ( integer( Index ) -> % Case 1: "test"
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%% Index >= Lower,
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%% Index =< Upper
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%% ; var( Index ) -> % Case 2: "generate".
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%% generate_between( Lower, Upper, Index )
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%% ).
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generate_between( Lower, Upper, Index ) :-
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( Lower =:= Upper ->
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Index = Lower
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; Index = Lower
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; Next is Lower + 1,
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Next =< Upper,
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generate_between( Next, Upper, Index )
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).
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% sum( +List, ?Sum ) holds when the List of numbers sum to Sum.
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sum( [H|T], Sum ) :-
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sum1( T, H, Sum ).
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sum1( [], Sum, Sum ).
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sum1( [H|T], Sum0, Sum ):-
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Sum1 is Sum0 + H,
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sum1( T, Sum1, Sum ).
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% put_chars( +Chars ) if Chars is a (possibly empty) list of character codes and the
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% corresponding characters are written to the current output stream.
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put_chars( [] ).
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put_chars( [Char|Chars] ) :-
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put( Char ),
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put_chars( Chars ).
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% get_chars( ?Chars ) if Chars is a (possibly empty) list of character codes read
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% from the current input stream.
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get_chars( Input ) :-
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get0( Char ),
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( Char > -1 ->
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Input = [Char|Chars],
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get_chars( Chars )
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; otherwise ->
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Input = []
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).
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