4 (and (list? t) (eq? (car t) 'abs)))
7 (and (not (list? t)) (not (concrete? t)) (symbol? t)))
15 (define (pretty-type t)
19 (string-append "(" (pretty-type (cadr t)) ")")
20 (pretty-type (cadr t)))
22 (pretty-type (caddr t))))
23 (else (symbol->string t))))
26 (define (env-lookup env n)
27 (if (null? env) (error #f "empty env") ; it's a type equality
28 (if (eq? (caar env) n)
30 (env-lookup (cdr env) n))))
32 (define (env-insert env n t)
33 (cons (cons n t) env))
40 (set! cur-tvar (+ cur-tvar 1))
42 (string-append "t" (number->string (- cur-tvar 1))))))
50 (define (normalize prog) ; (+ a b) -> ((+ a) b)
53 ; (lambda (x y) (+ x y)) -> (lambda (x) (lambda (y) (+ x y)))
54 (if (> (length (lambda-args prog)) 1)
55 (list 'lambda (list (car (lambda-args prog)))
56 (normalize (list 'lambda (cdr (lambda-args prog)) (caddr prog))))
57 (list 'lambda (lambda-args prog) (normalize (caddr prog)))))
59 (if (null? (cddr prog))
60 `(,(normalize (car prog)) ,(normalize (cadr prog))) ; (f a)
61 `(,(list (normalize (car prog)) (normalize (cadr prog)))
62 ,(normalize (caddr prog))))) ; (f a b)
63 ;; (list (list (normalize (car prog))
64 ;; (normalize (cadr prog))) (normalize (caddr prog))))) ; (f a b)
67 (map (lambda (x) `(,(car x) ,(normalize (cadr x))))
69 (map normalize (let-body prog))))
70 ('if `(if ,(normalize (cadr prog))
71 ,(normalize (caddr prog))
72 ,(normalize (cadddr prog))))
75 (define (builtin-type x)
77 ('+ '(abs int (abs int int)))
78 ('- '(abs int (abs int int)))
79 ('* '(abs int (abs int int)))
81 ('= '(abs int (abs int bool)))
82 ('bool->int '(abs bool int))
85 ; we typecheck the lambda calculus only (only single arg lambdas)
86 (define (typecheck prog)
88 ;; (display "check: ")
96 ('int-literal (list '() 'int))
97 ('bool-literal (list '() 'bool))
98 ('builtin (list '() (builtin-type x)))
101 (let* ((cond-type-res (check env (cadr x)))
102 (then-type-res (check env (caddr x)))
103 (else-type-res (check env (cadddr x)))
104 (then-eq-else-cs (unify (cadr then-type-res)
105 (cadr else-type-res)))
108 (consolidate (car else-type-res)
110 (return-type (substitute cs (cadr then-type-res))))
111 (when (not (eqv? (cadr cond-type-res) 'bool))
112 (error #f "if condition isn't bool"))
113 (list cs return-type)))
115 ('var (list '() (env-lookup env x)))
117 (let ((new-env (fold-left
120 (env-insert acc (car bind) (fresh-tvar))
122 (env-insert acc (car bind) (cadr t))))
123 env (let-bindings x))))
124 (check new-env (last (let-body x)))))
128 (let* ((new-env (env-insert env (lambda-arg x) (fresh-tvar)))
129 (body-type-res (check new-env (lambda-body x)))
130 (cs (car body-type-res))
131 (subd-env (substitute-env (car body-type-res) new-env))
132 (arg-type (env-lookup subd-env (lambda-arg x)))
133 (resolved-arg-type (substitute cs arg-type)))
134 ;; (display "lambda:\n\t")
139 ;; (display resolved-arg-type)
141 (list (car body-type-res)
144 (cadr body-type-res)))))
147 (let* ((arg-type-res (check env (cadr x)))
148 (arg-type (cadr arg-type-res))
149 (func-type-res (check env (car x)))
150 (func-type (cadr func-type-res))
153 (func-c (unify func-type
158 (consolidate func-c (car arg-type-res))
159 (car func-type-res)))
161 (resolved-func-type (substitute cs func-type))
162 (resolved-return-type (caddr resolved-func-type)))
163 ;; (display "app:\n")
166 ;; (display func-type)
168 ;; (display resolved-func-type)
170 ;; (display arg-type-res)
172 (if (abs? resolved-func-type)
173 (let ((return-type (substitute cs (caddr resolved-func-type))))
174 (list cs return-type))
175 (error #f "not a function")))))))
176 ;; (display "result of ")
179 ;; (display (cadr res))
181 ;; (display (car res))
184 (cadr (check '() (normalize prog))))
186 ; returns a list of pairs of constraints
188 (cond ((eq? a b) '())
189 ((or (tvar? a) (tvar? b)) (~ a b))
190 ((and (abs? a) (abs? b))
191 (consolidate (unify (cadr a) (cadr b))
192 (unify (caddr a) (caddr b))))
193 (else (error #f "could not unify"))))
195 ; TODO: what's the most appropriate substitution?
196 ; should all constraints just be limited to a pair?
197 (define (substitute cs t)
198 ; gets the first concrete type
199 ; otherwise returns the last type variable
201 (define (get-concrete c)
202 (let ((last (null? (cdr c))))
203 (if (not (tvar? (car c)))
205 (substitute cs (car c))
209 (get-concrete (cdr c))))))
212 (substitute cs (cadr t))
213 (substitute cs (caddr t))))
222 (define (substitute-env cs env)
223 (map (lambda (x) (cons (car x) (substitute cs (cdr x)))) env))
228 (define (consolidate x y)
232 (else (if (member (car b) a)
234 (cons (car b) (merge a (cdr b)))))))
235 (define (overlap? a b)
236 (if (or (null? a) (null? b))
238 (if (fold-left (lambda (acc v)
239 (or acc (eq? v (car a))))
242 (overlap? (cdr a) b))))
246 (else (let* ((a (car y))
256 (filter (lambda (b) (not (eq? b (cdr merged)))) x)
259 (consolidate removed (cons (car merged) (cdr y)))
260 (consolidate (cons a x) (cdr y)))))))