`t-sort`

Location: lib, 82 Lines

; Scheme 9 from Empty Space, Function Library ; By Nils M Holm, 2010,2012 ; Placed in the Public Domain ; ; (t-sort procedure1 object procedure2 <option> ...) ==> list ; (t-sort-net procedure^2 list <option> ...) ==> list ; ; Sort the directed acyclic graph (DAG) LIST topologically in ; such a way that all dependencies of the first node in the DAG ; (called the "goal") are resolved. PROCEDURE^2 is used to identify ; nodes in the DAG. ; ; A DAG is represented by a list of lists of the form ; ; ((<name-1> <ref> ...) ; ... ; (<name-N> <ref> ...)) ; ; where each <name-I> names a node of the DAG and each <ref> ; names a child of the node. Node <name-I> is said to depend on ; each <ref> in the same sublist. A node with zero <ref>s is a ; leaf node. ; ; When the 'STRICT keyword with a #T value is passed as an option ; argument to T-SORT-NET, it will operate in "strict mode" where each ; <ref> in the DAG must have a corresponding node. In non-strict ; operation undefined <ref>s are assumed to be leaves. ; ; T-SORT-NET returns #F when it cannot sort a given DAG, either because ; it contains undefined <refs> in strict mode or because it cycles (and ; hence is not a DAG at all). ; ; When 'CHECK #T is passed as an option to T-SORT-NET, it will return ; more useful information in case of an error, namely ; ; (cyclic . name) when the graph cycles through NAME ; (undefined . name) when node NAME is undefined. ; ; The result can be distinguished from success by the fact that ; the cdr of a negative result is not a pair. ; ; When the 'REVERSE #T option is passed to T-SORT-NET, it will list ; each dependent object before its dependencies. ; ; When the 'TOP-DOWN #T option is passed to T-SORT-NET, it will ; preserve the order of dependencies and the hierarchy of the ; net to sort, i.e. objects closer to the goal will appear last ; in the resulting list (or first, if 'REVERSE #T is also given). ; ; T-SORT is a more general version of T-SORT-NET that allows to sort ; structures without knowing their exact internal representation. ; PROCEDURE1 is the predicate used to compare objects, like in ; T-SORT-NET. OBJECT is the goal. PROCEDURE2 is a procedure that maps ; objects to dependencies their associated dependencies. The procedure ; should return #F when a dependency cannot be resolved. In case of ; success, it delivers a list of the form ; ; (goal object ...) ; ; GOAL is the goal that has been looked up and each OBJECT is an ; object on which the goal depends. ; ; Example: (t-sort-net eq? ; '((dressed shoes hat) ; (shoes socks pants) ; (pants underpants) ; (hat pullover) ; (pullover shirt undershirt) ; (shirt undershirt) ; (underpants))) ==> (socks underpants pants ; shoes undershirt shirt ; pullover hat dressed) ; ; (let ((db '((a b c) ; (b u) ; (c v) ; (u x) ; (v y) ; (w z)))) ; (t-sort eq? 'a (lambda (x) ; (assq x db)) ; 'top-down #t ; 'reverse #t)) ==> (a b c u v x y) ; ; (t-sort-net eq? '((a b c d))) ==> (b c d a) ; (t-sort-net eq? '((a b c d)) 'strict #t) ==> #f ; (t-sort-net eq? '((a b) (b a))) ==> #f ; (t-sort-net eq? '((foo foo)) 'check #t) ==> (cyclic . foo) (load-from-library "letcc.scm") (load-from-library "assp.scm") (load-from-library "memp.scm") (load-from-library "hash-table.scm") (load-from-library "keyword-value.scm") (define(t-sort p goal lookup . opts) (let/cc exit (let((visited (make-hash-table'test p)) (_ (accept-keywords "t-sort" opts'(strict check reverse top-down))) (strict (keyword-value opts'strict #f)) (check (keyword-value opts'check #f)) (rev-order (keyword-value opts'reverse #f)) (top-down (keyword-value opts'top-down #f))) (letrec((find-dep (lambda(x) (cond((lookup x)=>(lambda(x) x)) (strict (exit (ifcheck`(undefined .,dep) #f))) (else '())))) (sort-bu (lambda(dep) (cond((pair? dep) (let((res (apply append (map sort-bu (cdr dep))))) (if(memp p (car dep) res) (exit (ifcheck`(cyclic .,(car dep)) #f))) (ifrev-order (append (list (car dep)) res) (append res (list (car dep)))))) ((hash-table-ref visited dep)'()) (else(hash-table-set! visited dep #t) (let((new-dep (find-dep dep))) (cond((null? new-dep) (list dep)) ((null? (cdr new-dep)) (list (car new-dep))) (else(sort-bu new-dep)))))))) (sort-td (lambda(dep) (cond((pair? dep) (if(hash-table-ref visited dep) (exit (ifcheck`(cyclic .,dep) #f))) (hash-table-set! visited dep #t) (let*((res (map sort-td dep)) (res (map (lambda(x) (if(null? x)'() (cdr x))) res)) (res (apply append res))) (append dep (sort-td res)))) (else(find-dep dep)))))) (iftop-down (let*((dep (find-dep goal)) (res (cons (car dep) (sort-td (cdr dep)))) (res (list->set res))) (ifrev-order res (reverse res))) (sort-bu (find-dep goal))))))) (define(t-sort-net p net . opts) (apply t-sort p (caar net) (lambda(x) (assp p x net)) opts))