# chicken-digraph
Scheme implementation of a directed graph in adjacency list format
The `digraph` library is an implementation of a directed graph, where
the edges are stored as adjacency lists indexed by node number.
## Directed graph procedures
The digraph object is created by procedure `make-digraph`:
make-digraph:: NAME INFO [NODE-LIST [SUCC-LIST [PRED-LIST]]] -> SELECTOR
where:
- `NAME` is the graph name (string or symbol)
- `INFO` is an optional metadata object of an arbitrary type or {{#f}}
- `NODE-LIST` is an optional list of nodes to be inserted in the graph; each element of the list must be of the form {{(N INFO)}} where {{N}} is a unique node number (integer), and {{INFO}} is an optional metadata object describing the node.
- `SUCC-LIST` and {{PRED-LIST}} can be used to define the graph edges upon graph creation. If supplied, these arguments must be lists in which every element is of the form {{(I J INFO)}}, where {{I}} and {{J}} are node numbers, and {{INFO}} is an optional metadata object.
The returned yasos object can take one of the following messages:
- 'name` : returns the graph name (string or symbol)
- 'info` : returns the graph metadata (arbitrary type)
- 'new-id!` : returns a procedure with no arguments, which returns the lowest available node number
- 'add-node!` : returns a procedure `LAMBDA N INFO` which inserts in the graph node with number `N` and metadata `INFO`- if the node already exists in the graph, it will be overwritten with the new metadata
- 'add-edge!` : returns a procedure `LAMBDA EDGE` which inserts in the graph the specifed edge- the edge is given by a list of the form `(I J INFO)`, where `I` and `J` are source and destination nodes, respectively, and `INFO` is edge metadata of arbitrary type
- 'remove-node!` : returns a procedure `LAMBDA N` which removes node `N` and all its edges from the graph
- 'nodes` : returns a procedure with no arguments, which returns a list with the nodes of the graph and their metadata
- 'edges` : returns a procedure with no arguments, which returns a list with the edges of the graph and their metadata
- 'roots` : returns a procedure with no arguments, which returns a list with all nodes in the graph that do not have an predecessor
- 'terminals` : returns a procedure with no arguments, which returns a list with all nodes in the graph that do not have a successor
- 'order` : returns a procedure with no arguments, which returns the number of nodes in the graph
- 'size` : returns a procedure with no arguments, which returns the number of edges in the graph
- 'capacity` : returns a procedure with no arguments, which returns the size of the underlying dynamic vector
- 'succ` : returns a procedure `LAMBDA N` which returns a list with the successor nodes of node `N`
- 'pred` : returns a procedure `LAMBDA N` which returns a list with the predecessor nodes of node `N`
- 'succ-list` : returns a procedure with no arguments which returns a list containing the successor nodes for each node.
- 'pred-list` : returns a procedure with no arguments which returns a list containing the predecessor nodes for each node.
- 'out-edges` : returns a procedure `LAMBDA N` which returns a list with the outgoing edges of node `N`
- 'in-edges` : returns a procedure `LAMBDA N` which returns a list with the incoming edges of node `N`
- 'has-edge` : returns a procedure `LAMBDA I J` which returns true if edge `I -> J` exists in the graph and false otherwise
- 'has-node` : returns a procedure `LAMBDA N` which returns true if node `N` exists in the graph and false otherwise
- 'node-info` : returns a procedure `LAMBDA N` which returns the metadata for node `N`
- 'node-info-set!` : returns a procedure `LAMBDA N V` which sets the metadata for node `N`
- 'fold-node` : returns an iterator procedure `LAMBDA F RES` which iterates over the nodes in the graph by invoking function `F` on the node number, metadata of each node, and accumulator variable `RES`
- 'fold-edge` : returns an iterator procedure `LAMBDA F RES` which iterates over the edges in the graph by invoking function `F` on each edge and accumulator variable `RES`
- 'foreach-node` : returns an iterator procedure `LAMBDA F` which iterates over the nodes in the graph by invoking function `F` on the node number and metadata of each node
- 'foreach-edge` : returns an iterator procedure `LAMBDA F` which iterates over the edges in the graph by invoking function `F` on each edge
- 'debug` : returns a list with the internal representation of the graph
## Examples
```scheme
;; example adapted from graph example in the Boost library documentation
(import srfi-1 digraph matchable)
(define g (make-digraph 'depgraph "dependency graph"))
(define used-by
(list
(cons 'dax_h 'foo_cpp) (cons 'dax_h 'bar_cpp) (cons 'dax_h 'yow_h)
(cons 'yow_h 'bar_cpp) (cons 'yow_h 'zag_cpp) (cons 'boz_h 'bar_cpp)
(cons 'boz_h 'zig_cpp) (cons 'boz_h 'zag_cpp) (cons 'zow_h 'foo_cpp)
(cons 'foo_cpp 'foo_o) (cons 'foo_o 'libfoobar_a)
(cons 'bar_cpp 'bar_o) (cons 'bar_o 'libfoobar_a)
(cons 'libfoobar_a 'libzigzag_a) (cons 'zig_cpp 'zig_o)
(cons 'zig_o 'libzigzag_a) (cons 'zag_cpp 'zag_o)
(cons 'zag_o 'libzigzag_a) (cons 'libzigzag_a 'killerapp)))
(define node-list (delete-duplicates
(concatenate (list (map car used-by) (map cdr used-by)))))
(define node-ids (list-tabulate (length node-list) values))
(for-each (lambda (i n) (add-node! g i n)) node-ids node-list)
(define node-map (zip node-list node-ids))
(for-each (lambda (e)
(match e ((ni . nj) (let ((i (car (alist-ref ni node-map)))
(j (car (alist-ref nj node-map))))
(add-edge! g (list i j (format "~A->~A" ni nj)))))
(else (error "invalid edge " e))))
used-by)
(print (nodes g))
(print (edges g))
(remove-node! g 0)
(print (nodes g))
(print (edges g))
```
## License
```
Copyright 2007-2018 Ivan Raikov.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or (at
your option) any later version.
This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
A full copy of the GPL license can be found at
.
```