-(define (app? x)
- (and (list? x) (>= (length x) 2) (not (eq? (car x) 'lambda))))
-
-(define (lambda? x)
- (and (list? x) (eq? (car x) 'lambda)))
-
-(define lambda-arg caadr)
-(define lambda-body caddr)
-
+(load "ast.scm")
; ('a, ('b, 'a))
-(define (env-lookup env x)
+(define (env-lookup env n)
(if (null? env) (error #f "empty env") ; it's a type equality
- (if (eq? (caar env) x)
+ (if (eq? (caar env) n)
(cdar env)
- (env-lookup (cdr env) x))))
+ (env-lookup (cdr env) n))))
+
+(define (env-insert env n t)
+ (cons (cons n t) env))
(define abs-arg cadr)
(string->symbol
(string-append "t" (number->string (- cur-tvar 1))))))
+(define (last xs)
+ (if (null? (cdr xs))
+ (car xs)
+ (last (cdr xs))))
+
(define (normalize prog) ; (+ a b) -> ((+ a) b)
(cond
- ((lambda? prog) '(lambda (lambda-arg prog) (normalize (lambda-body prog))))
+ ; (lambda (x y) (+ x y)) -> (lambda (x) (lambda (y) (+ x y)))
+ ((lambda? prog)
+ (if (> (length (lambda-args prog)) 1)
+ (list 'lambda (list (car (lambda-args prog)))
+ (normalize (list 'lambda (cdr (lambda-args prog)) (caddr prog))))
+ (list 'lambda (lambda-args prog) (normalize (caddr prog)))))
((app? prog)
(if (null? (cddr prog))
(cons (normalize (car prog)) (normalize (cdr prog))) ; (f a)
- (normalize (cons (cons (car prog) (list (cadr prog))) (cddr prog))))) ; (f a b)
+ (list (list (normalize (car prog)) (normalize (cadr prog))) (normalize (caddr prog))))) ; (f a b)
+ ((let? prog)
+ (append (list 'let
+ (map (lambda (x) (cons (car x) (normalize (cdr x))))
+ (let-bindings prog)))
+ (map normalize (let-body prog))))
(else prog)))
+; 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
(cond
((eq? x '+) (list '() '(abs int (abs int int))))
((symbol? x) (list '() (env-lookup env x)))
+ ((let? x)
+ (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))))
+ (check new-env (last (let-body x)))))
+
+
((lambda? x)
- (let* ((new-env (cons (cons (lambda-arg x) (fresh-tvar)) env))
+ (let* ((new-env (env-insert env (lambda-arg x) (fresh-tvar)))
(body-type-res (check new-env (lambda-body x)))
(subd-env (substitute-env (car body-type-res) new-env)))
- ;; (display "lambda: ")
- ;; (display body-type-res)
- ;; (display "\n")
- ;; (display subd-env)
- ;; (display "\n")
+ (display "lambda: ")
+ (display body-type-res)
+ (display "\n")
+ (display subd-env)
+ (display "\n")
(list (car body-type-res)
(list 'abs
(env-lookup subd-env (lambda-arg x))
(if (abs? resolved-func-type)
(let ((return-type (substitute cs (caddr resolved-func-type))))
(list cs return-type))
- (error #f "wah")))))))
- ;; (display "result of ")
- ;; (display x)
- ;; (display ":\n\t")
- ;; (display (cadr res))
- ;; (display "[")
- ;; (display (car res))
- ;; (display "]\n")
+ (error #f "not a function")))))))
+ (display "result of ")
+ (display x)
+ (display ":\n\t")
+ (display (cadr res))
+ (display "[")
+ (display (car res))
+ (display "]\n")
res))
(cadr (check '() (normalize prog))))
; TODO: what's the most appropriate substitution?
; should all constraints just be limited to a pair?
(define (substitute cs t)
- (define (blah c)
+ ; gets the first concrete type
+ ; otherwise returns the last type variable
+ (define (get-concrete c)
(if (null? (cdr c))
(car c)
(if (not (tvar? (car c)))
(car c)
- (blah (cdr c)))))
+ (get-concrete (cdr c)))))
(fold-left
(lambda (t c)
(if (member t c)
- (blah c)
+ (get-concrete c)
t))
t cs))