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library/digraph.m:
New module for directed graphs. This is essentially the relation
module but with more consistent terminology, and with argument
ordering that suits state variables. Other differences with the
relation module:
- The digraph_key type has a phantom type parameter, which helps to
ensure that keys from one digraph are not used with another digraph.
- Exports a version of digraph.reduced which also returns the mapping
between the original digraph keys and the new ones.
- The implementation of compose/3 doesn't try to use the "domain" and
"range" of the graphs (which is meaningless in the relation module
anyway).
- New, more efficient algorithm for is_dag/1. Correctness proof is
documented.
- components/2 uses a more efficient data representation, and avoids
some intermediate data structures.
- reduced/{2,3} avoids some intermediate data structures.
- tc/2 avoids some intermediate data structures.
library/library.m:
Add the new module.
library/relation.m:
Document that this module is deprecated in favour of digraph.
Flag relation.init/{0,1} as obsolete (it would be better to flag
the entire module, or the relation/1 type as obsolete, but Mercury
does not support this).
NEWS:
Mention that the new module supersedes relation.m and svrelation.m.
compiler/*.m:
profiler/*.m:
Use the digraph module rather than the relation module.