(case t
('int #t)
('bool #t)
+ ('void #t)
(else #f)))
(define (pretty-type t)
('app
(if (null? (cddr prog))
`(,(normalize (car prog)) ,(normalize (cadr prog))) ; (f a)
- `(,(list (normalize (car prog)) (normalize (cadr prog)))
- ,(normalize (caddr prog))))) ; (f a b)
+ (normalize `(,(list (normalize (car prog)) (normalize (cadr prog)))
+ ,@(cddr prog))))) ; (f a b)
('let
(append (list 'let
(map (lambda (x) `(,(car x) ,(normalize (cadr x))))
('! '(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)
(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)
+ (then-eq-else-cs (~ (cadr then-type-res)
(cadr else-type-res)))
(cs (consolidate
(car then-type-res)
('var (list '() (env-lookup env x)))
('let
- (let ((new-env (fold-left
- (lambda (acc bind)
- (let ((t (check
- (env-insert acc (car bind) (fresh-tvar))
- (cadr bind))))
- (env-insert acc (car bind) (cadr t))))
- env (let-bindings x))))
+ ; 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)
+ (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)]
+ ; typecheck each component
+ [type-results
+ (map
+ (lambda (c)
+ (let ([body (cadr (assoc c (let-bindings x)))])
+ (check scc-env body)))
+ comps)]
+ ; collect all the constraints in the scc
+ [cs
+ (fold-left
+ (lambda (acc res c)
+ (consolidate
+ acc
+ (consolidate (car res)
+ ; unify with tvars from scc-env
+ ; result ~ tvar
+ (~ (cadr res) (env-lookup scc-env c)))))
+ '() 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)])
+ new-env))]
+ [new-env (fold-left process-component env components)])
(check new-env (last (let-body x)))))
-
('lambda
- (let* ((new-env (env-insert env (lambda-arg x) (fresh-tvar)))
+ (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)))
+ (resolved-arg-type (substitute cs arg-type))]
;; (display "lambda:\n\t")
;; (display prog)
;; (display "\n\t")
(cadr body-type-res)))))
('app ; (f a)
+ (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 (~ func-type other-func-type))
+ (resolved-return-type (substitute cs return-type))]
+ (list cs resolved-return-type))
+
+ ; 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))
; f ~ a -> t0
- (func-c (unify func-type
+ (func-c (~
+ func-type
(list 'abs
arg-type
(fresh-tvar))))
(if (abs? resolved-func-type)
(let ((return-type (substitute cs (caddr resolved-func-type))))
(list cs return-type))
- (error #f "not a function")))))))
+ (error #f "not a function"))))))))
;; (display "result of ")
;; (display x)
;; (display ":\n\t")
- ;; (display (cadr res))
- ;; (display "[")
+ ;; (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))
- (consolidate (unify (cadr a) (cadr b))
- (unify (caddr a) (caddr b))))
- (else (error #f "could not unify"))))
+(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) '()]
+ [(or (tvar? a) (tvar? b)) (list (list 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 #f]))
; TODO: what's the most appropriate substitution?
; should all constraints just be limited to a pair?
+ ; this is currently horrific and i don't know what im doing.
+ ; should probably use ast-find here or during consolidation
+ ; to detect substitutions more than one layer deep
+ ; e.g. (abs t1 int) ~ (abs bool int)
+ ; substituting these constraints with t1 should resolve t1 with bool
(define (substitute cs t)
; gets the first concrete type
; otherwise returns the last type variable
+ ; removes t itself from cs, to prevent infinite recursion
+ (define cs-without-t
+ (map (lambda (c)
+ (filter (lambda (x) (not (eqv? t x))) c))
+ cs))
+
(define (get-concrete c)
- (let ((last (null? (cdr c))))
+ (let [(last (null? (cdr c)))]
(if (not (tvar? (car c)))
(if (abs? (car c))
- (substitute cs (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))
(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)
(cond ((null? y) x)
((null? x) y)
- (else (let* ((a (car y))
+ (else
+ (let* ((a (car y))
(merged (fold-left
(lambda (acc b)
(if acc
(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
+(define (types-equal? x y)
+ (let ([cs (unify? x y)])
+ (if (not cs) #f
+ (let*
+ ([test-kind
+ (lambda (acc c)
+ (if (tvar? c) acc #f))]
+ [test (lambda (acc c)
+ (and acc
+ (fold-left test-kind #t c) ; check only tvar substitutions
+ (<= (length c) 2)))]) ; check maximum 2 subs per equality group
+ (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 (go bs orig-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 orig-bs) (list x) '())]
+ [else '()]))
+ prog))
+ (if (null? bs)
+ '(() . ())
+ (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 '() '())
+ (go (cdr bs) orig-bs)))
+ (total-verts (cons vert (car rest)))
+ (total-edges (append edges (cdr rest)))]
+ (cons total-verts total-edges))))
+ (go bs bs))
+
+(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