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a feature that is particularly interesting for generating integers from a certain value.
... in failure-driven loops.
But failure-driven loops are not particularly interesting (in fact, they are dangerous in practice as they can quickly morph into infinite loops amazingly easily).
Some potentially useful notes
Extension of between∕3: a "between" which also takes a negative or positive "step" value
Values are no pre-generated with between/3 and then linearly transformed, but properly generated "on need".
These are defined:
?- between(10,20,3,L). L = 10 ; L = 13 ; L = 16 ; L = 19.
?- between(10,-10,-3,L). L = 10 ; L = 7 ; L = 4 ; L = 1 ; L = -2 ; L = -5 ; L = -8.
Extension of between∕3: a "between" which which is able to propose valid intervals
The standard between/3 dataflow allows only to flow from a known
(LowerLimit,UpperLimit) to a sequence of Value.
Why not allow alternative directions:
(LowerLimit,Value)to a sequence of UpperLimit
(UpperLimit,Value)to a sequence of LowerLimit
- Value to a sequence of
These are defined:
- `between_x(?Low, ?High, ?Value)`
For example, define:
intervalsize(_,inf,inf) :- !. intervalsize(Lower,Upper,Size) :- Size is Upper-Lower+1.
Then generate intervals around 0 (below, the printout has been rearranged by hand):
?- between_x(Lower,Upper,0), intervalsize(Lower,Upper,Size), format("~q:[~q,~q]\n",[Size,Lower,Upper]). 1:[0,0] 2:[-1,0] 2:[0,1] 3:[-2,0] 3:[-1,1] 3:[0,2] 4:[-3,0] 4:[-2,1] 4:[-1,2] 4:[0,3] 5:[-4,0] 5:[-3,1] 5:[-2,2] 5:[-1,3] 5:[0,4] ...
Why doesn't this exist
Instead of trying puzzling code to obtain a list of integers:
% ============================================================================ % Create a list of integers, monotonically increasing by 1. % % TODO: Make it work in "reverse direction", too. % TODO: A lazy list using freeze/2 that generates the next integer on need % % create_list_of_integers_between(+Low,+High,?List) % % create_list_of_integers_between(+HighInclusive:['high_yes','high_no'],+Low,+High,?List) % ============================================================================ list_of_integers_between(Low,High,List) :- list_of_integers_between(high_yes,Low,High,List). list_of_integers_between(high_yes,Low,High,List) :- !, bagof(X,between(Low,High,X),List). list_of_integers_between(high_no,Low,High,List) :- !, ActualHigh is High-1, bagof(X,between(Low,ActualHigh,X),List). list_of_integers_between(HighInclusive,_,_,_) :- domain_error([high_yes,high_no],HighInclusive).
?- list_of_integers_between(0,4,L). L = [0,1,2,3,4]. ?- list_of_integers_between(false,0,4,L). L = [0,1,2,3]. ?- list_of_integers_between(true,0,4,L). L = [0,1,2,3,4].
What would also be nice
A between/5 for which one can specify whether the interval limit is inclusive or exclusive, because performing +1 / -1 operations is a bit annoying.
Then one could do
to get the behaviour of