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Merge pull request #740 from triska/indexing

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small documentation improvements related to the new indexing strategy
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Mark Thom
2020-12-22 15:39:17 -07:00
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parent 342b4a3b52 1c76c869ef
commit d290596c1d
1 changed files with 7 additions and 8 deletions
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README.md
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@@ -233,24 +233,23 @@ in all clauses of a predicate's definition. We call this strategy
first *instantiated* argument indexing. first *instantiated* argument indexing.
A key motivation for first instantiated argument indexing is to enable A key motivation for first instantiated argument indexing is to enable
indexing for meta-predicates such as `maplist/N` and `foldl/N`, where indexing for meta-predicates such as `maplist/N` and `foldl/N`, whose
the first argument is a goal or partial goal that is a variable in the first argument is a partial goal that is a variable in the definition
definition of these predicates and therefore cannot be used for of these predicates and therefore cannot be used for indexing.
indexing.
For example, a natural definiton of `maplist/2` reads: For example, a natural definiton of `maplist/2` reads:
``` ```
maplist(_, []). maplist(_, []).
maplist(Goal, [L|Ls]) :- maplist(Goal_1, [L|Ls]) :-
call(Goal, L), call(Goal_1, L),
maplist(Goal, Ls). maplist(Goal_1, Ls).
``` ```
In this case, first instantianted argument indexing automatically uses In this case, first instantianted argument indexing automatically uses
the *second* argument for indexing, and thus prevents choicepoints for the *second* argument for indexing, and thus prevents choicepoints for
calls with lists of fixed lengths (and deterministic goals). calls with lists of fixed lengths (and deterministic goals).
Conveniently, no auxiliary predicates with reorderd arguments are Conveniently, no auxiliary predicates with reordered arguments are
needed to benefit from indexing in such cases. needed to benefit from indexing in such cases.
Conventional first argument indexing naturally arises as a Conventional first argument indexing naturally arises as a