Module proto_vulcan::goal [−][src]
Expand description
Solvable goals
Proto-vulcan goals can be divided into two main categories: 1) breadth-first search (BFS) and 2) depth-first search (DFS) goals. The solutions to BFS goals are searched in the usual miniKanren-style interleaved fashion, whereas solutions to DFS goals are searched in the Prolog-style depth-first fashion. Breadth-first search is fairer, and can provide solutions from multiple infinite streams in parallel, but requires more resources to maintain the parallel search streams. Depth-first search on the other hand requires less resources, but cannot handle infinite streams of solutions. If all solutions are needed, and the order does not matter, then DFS is recommended.
- BFS goals are represented by the
Goal<U, E>type. - DFS goals are represented by the
DFSGoal<U, E>type.
Proto-vulcan allows any branch in the tree of goals to be DFS; by default, queries
are BFS. Preventing embedding of BFS goals in DFS branches is enforced with Rust
typing. A branch can be made DFS with an operator that is strictly DFS, or with
the dfs-operator and inferred goals. The embedding of goals is controlled with
the GoalCast-trait; wherever a goal is a parameter of another goal, the macros
generate a GoalCast::cast_into(goal)-call to convert the parameter goal into
the kind of the parent goal constructor parameter.
Often an operator or relation can be either DFS or BFS; such goals can be wrapped
into InferredGoal<U, E, G> which is always cast into the search type of the
parent goal.
Re-exports
pub use crate::GoalCast;Structs
A wrapper for goals that can be either DFS or BFS.