# Functor Path.Check

    module Check: functor (G : sigtype t

    module V: Sig.COMPARABLE val iter_succ : (V.t -> unit) -> t -> V.t -> unitend) -> sig .. end

Check for a path.

Parameters: |
`G` | : | `sig type t module V : Sig.COMPARABLE val iter_succ : (V.t -> unit) -> t -> V.t -> unit end`

    type path_checker

the abstract data type of a path checker; this is a mutable data structure

    val create : Path.G.t -> path_checker

`create g` builds a new path checker for the graph `g`; if the graph is mutable, it must not be mutated while this path checker is in use (through the function `check_path` below).

    val check_path : path_checker -> G.V.t -> G.V.t -> bool

`check_path pc v1 v2` checks whether there is a path from `v1` to `v2` in the graph associated to the path checker `pc`.

Complexity: The path checker contains a cache of all results computed so far. This cache is implemented with a hash table so access in this cache is usually O(1). When the result is not in the cache, Dijkstra's algorithm is run to check for the path, and all intermediate results are cached.

Note: if checks are to be done for almost all pairs of vertices, it may be more efficient to compute the transitive closure of the graph (see module `Oper`).