IN: graphs
USING: help.markup help.syntax kernel assocs hashtables ;

ARTICLE: "graphs" "Directed graph utilities"
"Words for treating associative mappings as directed graphs can be found in the " { $vocab-link "graphs" } " vocabulary. A directed graph is represented as an assoc mapping each vertex to a set of edges entering that vertex, where the set is itself an assoc, with equal keys and values."
$nl
"To create a new graph, just create an assoc, for example by calling " { $link <hashtable> } ". To add vertices and edges to a graph:"
{ $subsection add-vertex }
"To remove vertices from the graph:"
{ $subsection remove-vertex }
"Since graphs are represented as assocs, they can be cleared out by calling " { $link clear-assoc } "."
$nl
"You can perform queries on the graph:"
{ $subsection closure }
"Directed graphs are used to maintain cross-referencing information for " { $link "definitions" } "." ;

ABOUT: "graphs"

HELP: graph
{ $var-description "Temporary variable used by various graph words." } ;

HELP: add-vertex
{ $values { "vertex" object } { "edges" "a sequence" } { "graph" "an assoc mapping vertices to sequences of edges" } }
{ $description "Adds a vertex to a directed graph, with " { $snippet "edges" } "  as the outward edges from the vertex." }
{ $side-effects "graph" } ;

HELP: remove-vertex
{ $values { "vertex" object } { "edges" "a sequence" } { "graph" "an assoc mapping vertices to sequences of edges" } }
{ $description "Removes a vertex from a graph, using the given edges sequence." } 
{ $notes "The " { $snippet "edges" } " sequence must equal the value passed to " { $link add-vertex } ", otherwise some vertices of the graph may continue to refer to the removed vertex." }
{ $side-effects "graph" } ;

HELP: closure
{ $values { "obj" object } { "quot" "a a quotation with stack effect " { $snippet "( obj -- assoc )" } } { "assoc" "a new assoc" } }
{ $description "Outputs a set of all vertices reachable from " { $snippet "vertex" } " via edges given by the quotation. The set always includes " { $snippet "vertex" } "." } ;