(load "ast.scm")
+(load "stdlib.scm")
(define (abs? t)
(and (list? t) (eq? (car t) 'abs)))
(define (tvar? t)
- (and (not (list? t)) (not (concrete? t)) (symbol? t)))
+ (and (not (list? t))
+ (not (concrete? t))
+ (symbol? t)))
(define (concrete? t)
- (case t
- ('int #t)
- ('bool #t)
- ('void #t)
- (else #f)))
+ (and (symbol? t)
+ (char-upper-case? (string-ref (symbol->string t) 0))))
(define (pretty-type t)
(cond ((abs? t)
(pretty-type (caddr t))))
(else (symbol->string t))))
+(define (pretty-constraints cs)
+ (string-append "{"
+ (fold-left string-append
+ ""
+ (map (lambda (c)
+ (string-append
+ (pretty-type (car c))
+ ": "
+ (pretty-type (cdr c))
+ ", "))
+ cs))
+ "}"))
+
; ('a, ('b, 'a))
(define (env-lookup env n)
- (if (null? env) (error #f "empty env") ; it's a type equality
+ (if (null? env) (error #f "empty env" env n) ; it's a type equality
(if (eq? (caar env) n)
(cdar env)
(env-lookup (cdr env) n))))
(define (builtin-type x)
(case x
- ('+ '(abs int (abs int int)))
- ('- '(abs int (abs int int)))
- ('* '(abs int (abs int int)))
- ('! '(abs bool bool))
- ('= '(abs int (abs int bool)))
- ('bool->int '(abs bool int))
- ('print '(abs string void))
- (else #f)))
-
-; we typecheck the lambda calculus only (only single arg lambdas)
-(define (typecheck prog)
- (define (check env x)
- (display "check: ")
- (display x)
- (display "\n\t")
- (display env)
- (newline)
- (let
- ((res
- (case (ast-type x)
- ('int-literal (list '() 'int))
- ('bool-literal (list '() 'bool))
- ('string-literal (list '() 'string))
- ('builtin (list '() (builtin-type x)))
-
- ('if
- (let* ((cond-type-res (check env (cadr x)))
- (then-type-res (check env (caddr x)))
- (else-type-res (check env (cadddr x)))
- (then-eq-else-cs (unify (cadr then-type-res)
- (cadr else-type-res)))
- (cs (consolidate
- (car then-type-res)
- (consolidate (car else-type-res)
- then-eq-else-cs)))
- (return-type (substitute cs (cadr then-type-res))))
- (when (not (eqv? (cadr cond-type-res) 'bool))
- (error #f "if condition isn't bool"))
- (list cs return-type)))
-
- ('var (list '() (env-lookup env x)))
- ('let
- ; takes in the current environment and a scc
- ; returns new environment with scc's types added in
- (let* ([components (reverse (sccs (graph (let-bindings x))))]
- [process-component
- (lambda (acc comps)
- (display comps)
- (newline)
+ ('+ '(abs Int (abs Int Int)))
+ ('- '(abs Int (abs Int Int)))
+ ('* '(abs Int (abs Int Int)))
+ ('! '(abs Bool Bool))
+ ('= '(abs Int (abs Int Bool)))
+ ('bool->int '(abs Bool Int))
+ ('print '(abs String Void))
+ (else (error #f "Couldn't find type for builtin" x))))
+
+(define (check-let dls env x)
+
+ ; acc is a pair of (env . annotated bindings)
+ (define (process-component acc comps)
(let*
+ ; create a new env with tvars for each component
+ ; e.g. scc of (x y)
+ ; scc-env = ((x . t0) (y . t1))
([scc-env
(fold-left
(lambda (acc c)
(env-insert acc c (fresh-tvar)))
- acc comps)]
+ (car acc) comps)]
+ ; typecheck each component
[type-results
(map
(lambda (c)
- (begin (display scc-env) (newline)
(let ([body (cadr (assoc c (let-bindings x)))])
- (display body)(newline)(check scc-env body))))
+ (check dls scc-env body)))
comps)]
+ ; collect all the constraints in the scc
[cs
(fold-left
(lambda (acc res c)
- (consolidate
- acc
- (unify (cadr res) (env-lookup scc-env c))))
- '() type-results comps)])
- (display "process-component env:\n")
- (display (substitute-env cs scc-env))
- (newline)
- (substitute-env cs scc-env)))]
- [new-env (fold-left process-component env components)])
- (check new-env (last (let-body x)))))
-
- ;; (let ((new-env (fold-left
- ;; (lambda (acc bind)
- ;; (let* [(bind-tvar (fresh-tvar))
- ;; (env-with-tvar (env-insert acc (car bind) bind-tvar))
- ;; (bind-res (check env-with-tvar (cadr bind)))
- ;; (bind-type (cadr bind-res))
- ;; (cs (consolidate (car bind-res)
- ;; (unify bind-type bind-tvar)))]
- ;; (substitute-env cs env-with-tvar)))
- ;; env (let-bindings x))))
- ;; (display "sccs of graph\n")
- ;; (display (sccs (graph (let-bindings x))))
- ;; (newline)
- ;; (display "env when checking body:\n\t")
- ;; (display new-env)
- ;; (newline)
- ;; (check new-env (last (let-body x)))))
+ (constraint-merge
+ (constraint-merge
+ ; unify with tvars from scc-env
+ ; result ~ tvar
+ (~ (env-lookup scc-env c) (cadr res))
+ (car res))
+ acc))
+ '() type-results comps)]
+ ; substitute *only* the bindings in this scc
+ [new-env
+ (map (lambda (x)
+ (if (memv (car x) comps)
+ (cons (car x) (substitute cs (cdr x)))
+ x))
+ scc-env)]
+
+ [annotated-bindings (append (cdr acc) ; the previous annotated bindings
+ (map list
+ comps
+ (map caddr type-results)))])
+ (cons new-env annotated-bindings)))
+ ; takes in the current environment and a scc
+ ; returns new environment with scc's types added in
+ (let* ([components (reverse (sccs (graph (let-bindings x))))]
+ [results (fold-left process-component (cons env '()) components)]
+ [new-env (car results)]
+ [annotated-bindings (cdr results)]
+ [body-results (map (lambda (body) (check dls new-env body)) (let-body x))]
+ [let-type (cadr (last body-results))]
+ [cs (fold-left (lambda (acc cs) (constraint-merge acc cs)) '() (map car body-results))]
- ('lambda
- (let* [(new-env (env-insert env (lambda-arg x) (fresh-tvar)))
-
- (body-type-res (check new-env (lambda-body x)))
- (cs (car body-type-res))
- (subd-env (substitute-env (car body-type-res) new-env))
- (arg-type (env-lookup subd-env (lambda-arg x)))
- (resolved-arg-type (substitute cs arg-type))]
- ;; (display "lambda:\n\t")
- ;; (display prog)
- ;; (display "\n\t")
- ;; (display cs)
- ;; (display "\n\t")
- ;; (display resolved-arg-type)
- ;; (newline)
- (list (car body-type-res)
- (list 'abs
- resolved-arg-type
- (cadr body-type-res)))))
+ [annotated `((let ,annotated-bindings ,@(map caddr body-results)) : ,let-type)])
+ (list cs let-type annotated)))
- ('app ; (f a)
+(define (check-app dls env x)
(if (eqv? (car x) (cadr x))
; recursive function (f f)
- (let* [(func-type (env-lookup env (car x)))
- (return-type (fresh-tvar))
- (other-func-type `(abs ,func-type ,return-type))
- (cs (unify func-type other-func-type))]
- (list cs return-type))
+ ; TODO: what about ((f a) f)????
+ (let* ([func-type (env-lookup env (car x))]
+ [return-type (fresh-tvar)]
+ [other-func-type `(abs ,func-type ,return-type)]
+ [cs (~ func-type other-func-type)]
+ [resolved-return-type (substitute cs return-type)]
+
+ [annotated `(((,(car x) : ,func-type)
+ (,(cadr x) : ,func-type)) : ,resolved-return-type)])
+ (list cs resolved-return-type annotated)))
; regular function
- (let* ((arg-type-res (check env (cadr x)))
- (arg-type (cadr arg-type-res))
- (func-type-res (check env (car x)))
- (func-type (cadr func-type-res))
+ (let* ([arg-type-res (check dls env (cadr x))]
+ [arg-type (cadr arg-type-res)]
+ [func-type-res (check dls env (car x))]
+ [func-type (cadr func-type-res)]
; f ~ a -> t0
- (func-c (unify func-type
- (list 'abs
- arg-type
- (fresh-tvar))))
- (cs (consolidate
- (consolidate func-c (car arg-type-res))
- (car func-type-res)))
-
- (resolved-func-type (substitute cs func-type))
- (resolved-return-type (caddr resolved-func-type)))
- ;; (display "app:\n")
- ;; (display cs)
- ;; (display "\n")
- ;; (display func-type)
- ;; (display "\n")
- ;; (display resolved-func-type)
- ;; (display "\n")
- ;; (display arg-type-res)
- ;; (display "\n")
+ [func-c (~
+ (substitute (car arg-type-res) func-type)
+ `(abs ,arg-type ,(fresh-tvar)))]
+ [cs (constraint-merge
+ (constraint-merge func-c (car arg-type-res))
+ (car func-type-res))]
+
+ [resolved-func-type (substitute cs func-type)]
+ [resolved-return-type (caddr resolved-func-type)]
+
+ [annotated `((,(caddr func-type-res)
+ ,(caddr arg-type-res)) : ,resolved-return-type)])
+
(if (abs? resolved-func-type)
(let ((return-type (substitute cs (caddr resolved-func-type))))
- (list cs return-type))
- (error #f "not a function"))))))))
- (display "result of ")
- (display x)
- (display ":\n\t")
- (display (pretty-type (cadr res)))
- (display "\n\t[")
- (display (car res))
- (display "]\n")
- res))
- (cadr (check '() (normalize prog))))
-
- ; returns a list of pairs of constraints
-(define (unify a b)
- (cond ((eq? a b) '())
- ((or (tvar? a) (tvar? b)) (~ a b))
- ((and (abs? a) (abs? b))
- (let* [(arg-cs (unify (cadr a) (cadr b)))
- (body-cs (unify (substitute arg-cs (caddr a))
- (substitute arg-cs (caddr b))))]
- (consolidate arg-cs body-cs)))
- (else (error #f "could not unify"))))
+ (list cs return-type annotated))
+ (error #f "not a function"))))
+
+(define (check-case dls env x)
+
+ (define (check-match switch-type x)
+
+ (define (get-bindings product-types pattern)
+ (define (go product-type product)
+ (case (ast-type product)
+ ['var (list (cons product product-type))]
+ ; an inner pattern match
+ ['app (let* ([inner-sum (car product)]
+ [inner-sums (cdr (assoc product-type dls))]
+ [inner-product-types (cdr (assoc inner-sum inner-sums))])
+ (get-bindings inner-product-types product))]
+ [else '()]))
+ (flat-map go product-types (cdr pattern)))
+
+
+ (let ([pattern (car x)]
+ [expr (cadr x)])
+ (case (ast-type pattern)
+ ['app
+ ; a pattern match with bindings
+ (let ([sum (assoc (car pattern) (cdr (assoc switch-type dls)))])
+ (unless sum (error #f "can't pattern match ~a with ~a" switch-type pattern))
+ (let* ([names (cdr pattern)]
+ [product-types (cdr sum)]
+ [new-env (append (get-bindings product-types pattern) env)])
+
+ (check dls new-env expr)))]
+ ; pattern match with binding and no constructor
+ ['var (check dls (env-insert env pattern switch-type) expr)]
+ ; a pattern match without bindings
+ [else (check dls env expr)])))
+
+ (let* ([switch-type-res (check dls env (case-switch x))]
+ [switch-type (cadr switch-type-res)]
+
+ [case-expr-type-res (map (lambda (x) (check-match switch-type x)) (case-cases x))]
+ [case-expr-types (map cadr case-expr-type-res)]
+
+ [case-expr-equality-cs (fold-left constraint-merge '()
+ (map (lambda (t) (~ t (car case-expr-types)))
+ (cdr case-expr-types)))]
+
+ [resolved-type (substitute case-expr-equality-cs (car case-expr-types))]
+
+ [annotated `((case ,(caddr switch-type-res)
+ ,@(map (lambda (c e et)
+ `(,c ((,e : ,et))))
+ (map car (case-cases x))
+ (map cadr (case-cases x))
+ case-expr-types)) : ,resolved-type)]
+
+ [cs (fold-left constraint-merge '()
+ (cons (car switch-type-res) case-expr-equality-cs))])
+ (list cs resolved-type annotated)))
+
+; returns a list (constraints type annotated)
+(define (check dls env x)
+ (define (make-result cs type)
+ (list cs type `(,x : ,type)))
+ ;; (display "check: ")
+ ;; (display x)
+ ;; (display "\n\t")
+ ;; (display env)
+ ;; (newline)
+ (let
+ ((res
+ (case (ast-type x)
+ ('int-literal (make-result '() 'Int))
+ ('string-literal (make-result '() 'String))
+ ('builtin (make-result '() (builtin-type x)))
- ; TODO: what's the most appropriate substitution?
- ; should all constraints just be limited to a pair?
-(define (substitute cs t)
- ; gets the first concrete type
- ; otherwise returns the last type variable
+ ('if
+ (let* ((cond-type-res (check dls env (cadr x)))
+ (then-type-res (check dls env (caddr x)))
+ (else-type-res (check dls env (cadddr x)))
+ (then-eq-else-cs (~ (cadr then-type-res)
+ (cadr else-type-res)))
+ (cs (constraint-merge
+ (car then-type-res)
+ (constraint-merge (~ (cadr cond-type-res) 'Bool)
+ (constraint-merge (car else-type-res)
+ then-eq-else-cs))))
+ (return-type (substitute cs (cadr then-type-res)))
+ [annotated `((if ,(caddr cond-type-res)
+ ,(caddr then-type-res)
+ ,(caddr else-type-res)) : ,return-type)])
+ (list cs return-type annotated)))
- (define cs-without-t
- (map (lambda (c)
- (filter (lambda (x) (not (eqv? t x))) c))
- cs))
+ ('var (make-result '() (env-lookup env x)))
+ ('let (check-let dls env x))
- (define (get-concrete c)
- (let [(last (null? (cdr c)))]
- (if (not (tvar? (car c)))
- (if (abs? (car c))
- (substitute cs-without-t (car c))
- (car c))
- (if last
- (car c)
- (get-concrete (cdr c))))))
- (cond
- ((abs? t) (list 'abs
- (substitute cs (cadr t))
- (substitute cs (caddr t))))
- (else
- (fold-left
- (lambda (t c)
- (if (member t c)
- (get-concrete c)
- t))
- t cs))))
+ ('lambda
+ (let* ([new-env (env-insert env (lambda-arg x) (fresh-tvar))]
+
+ [body-type-res (check dls new-env (lambda-body x))]
+ [cs (car body-type-res)]
+ [subd-env (substitute-env (car body-type-res) new-env)]
+ [arg-type (env-lookup subd-env (lambda-arg x))]
+ [resolved-arg-type (substitute cs arg-type)]
+
+ [lambda-type `(abs ,resolved-arg-type ,(cadr body-type-res))]
+
+ [annotated `((lambda (,(lambda-arg x)) ,(caddr body-type-res)) : ,lambda-type)])
+
+ (list (car body-type-res) ; constraints
+ lambda-type ; type
+ annotated)))
+
+
+ ('app (check-app dls env x))
+ ['case (check-case dls env x)])))
+
+ ;; (display "result of ")
+ ;; (display x)
+ ;; (display ":\n\t")
+ ;; (display (pretty-type (cadr res)))
+ ;; (display "\n\t[")
+ ;; (display (pretty-constraints (car res)))
+ ;; (display "]\n")
+ res))
+
+(define (init-adts-env prog)
+ (flat-map data-tors-type-env (program-data-layouts prog)))
+
+ ; we typecheck the lambda calculus only (only single arg lambdas)
+(define (typecheck prog-without-stdlib)
+ (let* ([prog (append stdlib prog-without-stdlib)]
+ [expanded (expand-pattern-matches prog)])
+ (cadr (check (program-data-layouts prog)
+ (init-adts-env expanded)
+ (normalize (program-body expanded))))))
+
+
+ ; before passing annotated types onto codegen
+ ; we need to restore the pre-normalization structure
+ ; (this is important for function arity etc)
+(define (denormalize orig normed)
+
+ (define (collapse-lambdas n x)
+ (case n
+ [0 x]
+ [else
+ (let* ([inner-lambda (lambda-body (ann-expr x))]
+ [arg (lambda-arg (ann-expr x))]
+ [inner-collapsed (ann-expr (collapse-lambdas (- n 1) inner-lambda))])
+ `((lambda ,(cons arg (lambda-args inner-collapsed))
+ ,(lambda-body inner-collapsed)) : ,(ann-type x)))]))
+
+ (define (collapse-apps n x)
+ (case n
+ [-1 (error #f "nullary functions not handled yet")]
+ [0 x]
+ [else
+ (let* ([inner-app (car (ann-expr x))]
+ [inner-collapsed (collapse-apps (- n 1) inner-app)])
+ `(,(append (ann-expr inner-collapsed) (cdr (ann-expr x))) : ,(ann-type x)))]))
+
+ (case (ast-type orig)
+ ['lambda
+ (let ([collapsed (collapse-lambdas (- (length (lambda-args orig)) 1) normed)])
+ `((lambda ,(lambda-args (ann-expr collapsed))
+ ,(denormalize (lambda-body orig)
+ (lambda-body (ann-expr collapsed)))) : ,(ann-type collapsed)))]
+ ['app
+ (let ([collapsed (collapse-apps (- (length orig) 2) normed)])
+ `(,(map (lambda (o n) (denormalize o n)) orig (ann-expr collapsed))
+ : ,(ann-type collapsed)))]
+ ['let
+ `((let ,(map (lambda (o n) (list (car o) (denormalize (cadr o) (cadr n))))
+ (let-bindings orig)
+ (let-bindings (ann-expr normed)))
+ ,@(map denormalize
+ (let-body orig)
+ (let-body (ann-expr normed)))) : ,(ann-type normed))]
+ ['if `((if ,@(map denormalize (cdr orig) (cdr (ann-expr normed))))
+ : ,(ann-type normed))]
+ ['case `((case ,(denormalize (case-switch orig) (case-switch (ann-expr normed)))
+ ,@(map (lambda (o n) (cons (car o) (denormalize (cadr o) (cadr n))))
+ (case-cases orig) (case-cases (ann-expr normed))))
+ : ,(ann-type normed))]
+ [else normed]))
+
+(define ann-expr car)
+(define ann-type caddr)
+
+ ; prerequisites: expand-pattern-matches
+(define (annotate-types prog)
+ (denormalize
+ (program-body prog)
+ (caddr (check (program-data-layouts prog)
+ (init-adts-env prog)
+ (normalize (program-body prog))))))
+
+
+ ; returns a list of constraints
+(define (~ a b)
+ (let ([res (unify? a b)])
+ (if res
+ res
+ (error #f
+ (format "couldn't unify ~a ~~ ~a" a b)))))
+
+(define (unify? a b)
+ (cond [(eq? a b) '()]
+ [(tvar? a) (list (cons a b))]
+ [(tvar? b) (list (cons b a))]
+ [(and (abs? a) (abs? b))
+ (let* [(arg-cs (unify? (cadr a) (cadr b)))
+ (body-cs (unify? (substitute arg-cs (caddr a))
+ (substitute arg-cs (caddr b))))]
+ (constraint-merge body-cs arg-cs))]
+ [else #f]))
+
+(define (substitute cs t)
+ (cond
+ [(tvar? t)
+ (if (assoc t cs)
+ (cdr (assoc t cs))
+ t)]
+ [(abs? t) `(abs ,(substitute cs (cadr t))
+ ,(substitute cs (caddr t)))]
+ [else t]))
+
+ ; applies substitutions to all variables in environment
(define (substitute-env cs env)
(map (lambda (x) (cons (car x) (substitute cs (cdr x)))) env))
-(define (~ a b)
- (list (list a b)))
-
-(define (consolidate x y)
- (define (merge a b)
- (cond ((null? a) b)
- ((null? b) a)
- (else (if (member (car b) a)
- (merge a (cdr b))
- (cons (car b) (merge a (cdr b)))))))
- (define (overlap? a b)
- (if (or (null? a) (null? b))
- #f
- (if (fold-left (lambda (acc v)
- (or acc (eq? v (car a))))
- #f b)
- #t
- (overlap? (cdr a) b))))
-
- (cond ((null? y) x)
- ((null? x) y)
- (else
- (let* ((a (car y))
- (merged (fold-left
- (lambda (acc b)
- (if acc
- acc
- (if (overlap? a b)
- (cons (merge a b) b)
- #f)))
- #f x))
- (removed (if merged
- (filter (lambda (b) (not (eq? b (cdr merged)))) x)
- x)))
- (if merged
- (consolidate removed (cons (car merged) (cdr y)))
- (consolidate (cons a x) (cdr y)))))))
-
- ; a1 -> a2 ~ a3 -> a4;
- ; a1 -> a2 !~ bool -> bool
- ; basically can the tvars be renamed
+ ; composes constraints a onto b and merges, i.e. applies a to b
+ ; a should be the "more important" constraints
+(define (constraint-merge a b)
+ (define (f cs constraint)
+ (cons (car constraint)
+ (substitute cs (cdr constraint))))
+
+ (define (most-concrete a b)
+ (cond
+ [(tvar? a) b]
+ [(tvar? b) a]
+ [(and (abs? a) (abs? b))
+ `(abs ,(most-concrete (cadr a) (cadr b))
+ ,(most-concrete (caddr a) (caddr b)))]
+ [(abs? a) b]
+ [(abs? b) a]
+ [else a]))
+
+ ; for any two constraints that clash, e.g. t1 ~ abs t2 t3
+ ; and t1 ~ abs int t3
+ ; prepend the most concrete version of the type to the
+ ; list of constraints
+ (define (clashes)
+ (define (gen acc x)
+ (if (assoc (car x) a)
+ (cons (cons (car x) (most-concrete (cdr (assoc (car x) a))
+ (cdr x)))
+ acc)
+ acc))
+ (fold-left gen '() b))
+
+ (define (union p q)
+ (append (filter (lambda (x) (not (assoc (car x) p)))
+ q)
+ p))
+ (append (clashes) (union a (map (lambda (z) (f a z)) b))))
+
+
+;; ; a1 -> a2 ~ a3 -> a4;
+;; ; a1 -> a2 !~ Bool -> Bool
+;; ; basically can the tvars be renamed
(define (types-equal? x y)
- (error #f "todo"))
+ (let ([cs (unify? x y)])
+ (if (not cs) #f
+ (let*
+ ([test (lambda (acc c)
+ (and acc
+ (tvar? (car c)) ; the only substitutions allowed are tvar -> tvar
+ (tvar? (cdr c))))])
+ (fold-left test #t cs)))))
; input: a list of binds ((x . y) (y . 3))
; returns: pair of verts, edges ((x y) . (x . y))
-(define (graph bs)
- (define (find-refs prog)
- (ast-collect
- (lambda (x)
- (case (ast-type x)
- ; only count a reference if its a binding
- ['var (if (assoc x bs) (list x) '())]
- [else '()]))
- prog))
- (let* [(bind (car bs))
-
- (vert (car bind))
- (refs (find-refs (cdr bind)))
- (edges (map (lambda (x) (cons vert x))
- refs))
-
- (rest (if (null? (cdr bs))
- (cons '() '())
- (graph (cdr bs))))
- (total-verts (cons vert (car rest)))
- (total-edges (append edges (cdr rest)))]
- (cons total-verts total-edges)))
-
-(define (successors graph v)
- (define (go v E)
- (if (null? E)
- '()
- (if (eqv? v (caar E))
- (cons (cdar E) (go v (cdr E)))
- (go v (cdr E)))))
- (go v (cdr graph)))
-
- ; takes in a graph (pair of vertices, edges)
- ; returns a list of strongly connected components
-
- ; ((x y w) . ((x . y) (x . w) (w . x))
-
- ; =>
- ; .->x->y
- ; | |
- ; | v
- ; .--w
-
- ; ((x w) (y))
-
- ; this uses tarjan's algorithm, to get reverse
- ; topological sorting for free
-(define (sccs graph)
-
- (let* ([indices (make-hash-table)]
- [lowlinks (make-hash-table)]
- [on-stack (make-hash-table)]
- [current 0]
- [stack '()]
- [result '()])
-
- (define (index v)
- (get-hash-table indices v #f))
- (define (lowlink v)
- (get-hash-table lowlinks v #f))
-
- (letrec
- ([strong-connect
- (lambda (v)
- (begin
- (put-hash-table! indices v current)
- (put-hash-table! lowlinks v current)
- (set! current (+ current 1))
- (push! stack v)
- (put-hash-table! on-stack v #t)
-
- (for-each
- (lambda (w)
- (if (not (hashtable-contains? indices w))
- ; successor w has not been visited, recurse
- (begin
- (strong-connect w)
- (put-hash-table! lowlinks
- v
- (min (lowlink v) (lowlink w))))
- ; successor w has been visited
- (when (get-hash-table on-stack w #f)
- (put-hash-table! lowlinks v (min (lowlink v) (index w))))))
- (successors graph v))
-
- (when (= (index v) (lowlink v))
- (let ([scc
- (let new-scc ()
- (let ([w (pop! stack)])
- (put-hash-table! on-stack w #f)
- (if (eqv? w v)
- (list w)
- (cons w (new-scc)))))])
- (set! result (cons scc result))))))])
-
- (for-each
- (lambda (v)
- (when (not (hashtable-contains? indices v)) ; v.index == -1
- (strong-connect v)))
- (car graph)))
- result))
projects / scheme.git / blobdiff