SYNOPSIS

     use Data::Graph::Util qw(toposort is_cyclic is_acyclic);
    
     my @sorted = toposort(
         { a=>["b"], b=>["c", "d"], d=>["c"] },
     ); # => ("a", "b", "d", "c")
    
     # sort specified nodes (nodes not mentioned in the graph will be put at the
     # end), duplicates not removed
     my @sorted = toposort(
         { a=>["b"], b=>["c", "d"], d=>["c"] },
         ["e", "a", "b", "a"]
     ); # => ("a", "a", "b", "e")
    
     say is_cyclic ({a=>["b"]}); # => 0
     say is_acyclic({a=>["b"]}); # => 1
    
     say is_cyclic ({a=>["b"], b=>["c"], c=>["a"]}); # => 1
     say is_acyclic({a=>["b"], b=>["c"], c=>["a"]}); # => 0

DESCRIPTION

    Early release. More functions will be added later.

FUNCTIONS

    None are exported by default, but they are exportable.

 toposort(\%graph[ , \@nodes ]) => sorted list

    Perform a topological sort on graph (currently using the Kahn
    algorithm). Will return the nodes of the graph sorted topologically.
    Will die if graph cannot be sorted, e.g. when graph is cyclic.

    If \@nodes is specified, will instead return @nodes sorted according to
    the topological order. Duplicates are allowed and not removed. Nodes
    not mentioned in graph are also allowed and will be put at the end.

 is_cyclic(\%graph) => bool

    Return true if graph contains at least one cycle. Currently implemented
    by attempting a topological sort on the graph. If it can't be
    performed, this means the graph contains cycle(s).

 is_acyclic(\%graph) => bool

    Return true if graph is acyclic, i.e. contains no cycles. The opposite
    of is_cyclic().

SEE ALSO

    https://en.wikipedia.org/wiki/Graph_(abstract_data_type)

    https://en.wikipedia.org/wiki/Topological_sorting#Kahn.27s_algorithm

    Sort::Topological can also sort a DAG, but cannot handle cyclical
    graph.