X-Git-Url: http://git.lukelau.me/?p=scheme.git;a=blobdiff_plain;f=typecheck.scm;h=197798e104a7595f5637646cb102f2d9d99f44d5;hp=98d1cf449fdaeed5f1b0f1eb22abf60a405d3a66;hb=21a9f0aaa56d6dd767cefb30c606f4c62eecff48;hpb=64e7552f99ab98b7db77797cecfc3f34331296df diff --git a/typecheck.scm b/typecheck.scm index 98d1cf4..197798e 100644 --- a/typecheck.scm +++ b/typecheck.scm @@ -1,4 +1,27 @@ (load "ast.scm") + +(define (abs? t) + (and (list? t) (eq? (car t) 'abs))) + +(define (tvar? t) + (and (not (list? t)) (not (concrete? t)) (symbol? t))) + +(define (concrete? t) + (case t + ('int #t) + ('bool #t) + (else #f))) + +(define (pretty-type t) + (cond ((abs? t) + (string-append + (if (abs? (cadr t)) + (string-append "(" (pretty-type (cadr t)) ")") + (pretty-type (cadr t))) + " -> " + (pretty-type (caddr t)))) + (else (symbol->string t)))) + ; ('a, ('b, 'a)) (define (env-lookup env n) (if (null? env) (error #f "empty env") ; it's a type equality @@ -25,43 +48,72 @@ (define (normalize prog) ; (+ a b) -> ((+ a) b) - (cond + (case (ast-type prog) + ('lambda ; (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) + ('app (if (null? (cddr prog)) - (cons (normalize (car prog)) (normalize (cdr prog))) ; (f a) - (list (list (normalize (car prog)) (normalize (cadr prog))) (normalize (caddr prog))))) ; (f a b) - ((let? prog) + `(,(normalize (car prog)) ,(normalize (cadr prog))) ; (f a) + `(,(list (normalize (car prog)) (normalize (cadr prog))) + ,(normalize (caddr prog))))) ; (f a b) + ;; (list (list (normalize (car prog)) + ;; (normalize (cadr prog))) (normalize (caddr prog))))) ; (f a b) + ('let (append (list 'let - (map (lambda (x) (cons (car x) (normalize (cdr x)))) + (map (lambda (x) `(,(car x) ,(normalize (cadr x)))) (let-bindings prog))) (map normalize (let-body prog)))) + ('if `(if ,(normalize (cadr prog)) + ,(normalize (caddr prog)) + ,(normalize (cadddr prog)))) (else prog))) +(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)) + (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) + ;; (display "check: ") + ;; (display x) + ;; (display "\n\t") + ;; (display env) + ;; (newline) (let ((res - (cond - ((integer? x) (list '() 'int)) - ((boolean? x) (list '() 'bool)) - ((eq? x 'inc) (list '() '(abs int int))) - ((eq? x '+) (list '() '(abs int (abs int int)))) - ((symbol? x) (list '() (env-lookup env x))) + (case (ast-type x) + ('int-literal (list '() 'int)) + ('bool-literal (list '() 'bool)) + ('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))) - ((let? x) + ('var (list '() (env-lookup env x))) + ('let (let ((new-env (fold-left (lambda (acc bind) (let ((t (check @@ -72,21 +124,26 @@ (check new-env (last (let-body x))))) - ((lambda? x) + ('lambda (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") + (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 - (env-lookup subd-env (lambda-arg x)) + resolved-arg-type (cadr body-type-res))))) - ((app? x) ; (f a) + ('app ; (f a) (let* ((arg-type-res (check env (cadr x))) (arg-type (cadr arg-type-res)) (func-type-res (check env (car x))) @@ -97,7 +154,9 @@ (list 'abs arg-type (fresh-tvar)))) - (cs (append func-c (car arg-type-res) (car func-type-res))) + (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))) @@ -114,29 +173,16 @@ (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 (cadr res)) - (display "[") - (display (car res)) - (display "]\n") + ;; (display "result of ") + ;; (display x) + ;; (display ":\n\t") + ;; (display (cadr res)) + ;; (display "[") + ;; (display (car res)) + ;; (display "]\n") res)) (cadr (check '() (normalize prog)))) - -(define (abs? t) - (and (list? t) (eq? (car t) 'abs))) - -(define (tvar? t) - (and (not (list? t)) (not (concrete? t)) (symbol? t))) - -(define (concrete? t) - (case t - ('int #t) - ('bool #t) - (else #f))) - ; returns a list of pairs of constraints (define (unify a b) (cond ((eq? a b) '()) @@ -146,24 +192,32 @@ (unify (caddr a) (caddr b)))) (else (error #f "could not unify")))) - ; 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 + (define (get-concrete c) - (if (null? (cdr c)) - (car c) + (let ((last (null? (cdr c)))) (if (not (tvar? (car c))) + (if (abs? (car c)) + (substitute cs (car c)) + (car c)) + (if last (car c) - (get-concrete (cdr 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)) + t cs)))) (define (substitute-env cs env) (map (lambda (x) (cons (car x) (substitute cs (cdr x)))) env))