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; Copyright (c) 1993-1999 by Richard Kelsey and Jonathan Rees. See file COPYING.
; Rudimentary type reconstruction, hardly worthy of the name.
; Currently, NODE-TYPE is called in two places. One is to determine
; the type of the right-hand side of a DEFINE for a variable that is
; never assigned, so uses of the variable can be checked later. The
; other is when compiling a call, to check types of arguments and
; produce warning messages.
; This is heuristic, to say the least. It's not clear what the right
; interface or formalism is for Scheme; I'm still experimenting.
; Obviously we can't do Hindley-Milner inference. Not only does
; Scheme have subtyping, but it also has dependent types up the wazoo.
; For example, the following is perfectly correct Scheme:
;
; (define (foo x y) (if (even? x) (car y) (vector-ref y 3)))
(define (node-type node)
(reconstruct node 'fast any-values-type))
(define (reconstruct-type node env)
(reconstruct node '() any-values-type))
(define (reconstruct node constrained want-type)
((operator-table-ref reconstructors (node-operator-id node))
node
constrained
want-type))
(define (examine node constrained want-type)
(if (pair? constrained)
(reconstruct node constrained want-type)
want-type))
(define reconstructors
(make-operator-table (lambda (node constrained want-type)
(reconstruct-call (node-form node)
constrained
want-type))))
(define (define-reconstructor name type proc)
(operator-define! reconstructors name type proc))
(define-reconstructor 'lambda syntax-type
(lambda (node constrained want-type)
(reconstruct-lambda node constrained want-type #f)))
(define-reconstructor 'flat-lambda syntax-type
(lambda (node constrained want-type)
(reconstruct-lambda node constrained want-type #f)))
(define (reconstruct-lambda node constrained want-type called?)
(if (eq? constrained 'fast)
any-procedure-type
(let* ((form (node-form node))
(want-result (careful-codomain want-type))
(formals (cadr form))
(alist (map (lambda (node)
(cons node value-type))
(normalize-formals formals)))
(cod (reconstruct (last form) ; works for normal and flat
(if called?
(append alist constrained)
alist)
want-result)))
(procedure-type (if (n-ary? formals)
any-values-type ;lose
(make-some-values-type (map cdr alist)))
cod
#t))))
(define (careful-codomain proc-type)
(if (procedure-type? proc-type)
(procedure-type-codomain proc-type)
any-values-type))
(define-reconstructor 'name 'leaf
(lambda (node constrained want-type)
(if (eq? constrained 'fast)
(reconstruct-name node)
(let ((z (assq node constrained)))
(if z
(let ((type (meet-type (cdr z) want-type)))
(begin (set-cdr! z type)
type))
(reconstruct-name node))))))
(define (reconstruct-name node)
(let ((probe (node-ref node 'binding)))
(if (binding? probe)
(let ((type (binding-type probe)))
(cond ((variable-type? type)
(variable-value-type type))
((subtype? type value-type)
type)
(else
value-type)))
value-type)))
(define-reconstructor 'call 'internal
(lambda (node constrained want-type)
(let ((form (node-form node)))
(cond ((proc->reconstructor (car form))
=> (lambda (recon)
(recon (cdr form) constrained want-type)))
(else
(reconstruct-call form constrained want-type))))))
; See if PROC is a primop or a variable bound to a primop, and then return
; that primops reconstructor, if it has one.
(define (proc->reconstructor proc)
(cond ((name-node? proc)
(let ((probe (node-ref proc 'binding)))
(if (and probe
(binding? probe)
(primop? (binding-static probe)))
(table-ref primop-reconstructors
(binding-static probe))
#f)))
((literal-node? proc)
(if (primop? (node-form proc))
(table-ref primop-reconstructors
(node-form proc))
#f))
(else #f)))
(define (reconstruct-call form constrained want-type)
(let* ((want-op-type (procedure-type any-arguments-type
want-type
#f))
(op-type (if (lambda-node? (car form))
(reconstruct-lambda (car form)
constrained
want-op-type
#t)
(reconstruct (car form)
constrained
want-op-type)))
(args (cdr form))
(lose (lambda ()
(for-each (lambda (arg)
(examine arg constrained value-type))
args))))
(if (procedure-type? op-type)
(begin (if (restrictive? op-type)
(let loop ((args args)
(dom (procedure-type-domain op-type)))
(if (not (or (null? args)
(empty-rail-type? dom)))
(begin (examine (car args)
constrained
(head-type dom))
(loop (cdr args) (tail-type dom)))))
(lose))
(procedure-type-codomain op-type))
(begin (lose)
any-values-type))))
(define-reconstructor 'literal 'leaf
(lambda (node constrained want-type)
(constant-type (node-form node))))
(define-reconstructor 'quote syntax-type
(lambda (node constrained want-type)
(constant-type (cadr (node-form node)))))
(define-reconstructor 'unspecific #f
(lambda (node constrained wnat-type)
unspecific-type))
(define-reconstructor 'unassigned #f
(lambda (node constrained wnat-type)
unspecific-type))
(define-reconstructor 'if syntax-type
(lambda (node constrained want-type)
(let ((form (node-form node)))
(examine (cadr form) constrained value-type)
;; Fork off two different constrain sets
(let ((con-alist (fork-constraints constrained))
(alt-alist (fork-constraints constrained)))
(let ((con-type (reconstruct (caddr form) con-alist want-type))
(alt-type (reconstruct (cadddr form) alt-alist want-type)))
(if (pair? constrained)
(for-each (lambda (c1 c2 c)
(set-cdr! c (join-type (cdr c1) (cdr c2))))
con-alist
alt-alist
constrained))
(join-type con-type alt-type))))))
(define (fork-constraints constrained)
(if (pair? constrained)
(map (lambda (x) (cons (car x) (cdr x)))
constrained)
constrained))-
(define-reconstructor 'begin syntax-type
(lambda (node constrained want-type)
;; This is unsound - there might be a throw out of some subform
;; other than the final one.
(do ((forms (cdr (node-form node)) (cdr forms)))
((null? (cdr forms))
(reconstruct (car forms) constrained want-type))
(examine (car forms) constrained any-values-type))))
(define-reconstructor 'set! syntax-type
(lambda (node constrained want-type)
(examine (caddr (node-form node)) constrained value-type)
unspecific-type))
(define-reconstructor 'letrec syntax-type
(lambda (node constrained want-type)
(let ((form (node-form node)))
(if (eq? constrained 'fast)
(reconstruct (caddr form) 'fast want-type)
(let ((alist (map (lambda (spec)
(cons (car spec)
(reconstruct (cadr spec)
constrained
value-type)))
(cadr form))))
(reconstruct (caddr form)
(append alist constrained)
want-type))))))
(define-reconstructor 'loophole syntax-type
(lambda (node constrained want-type)
(let ((args (cdr (node-form node))))
(examine (cadr args) constrained any-values-type)
(car args))))
(define (node->type node)
(if (node? node)
(let ((form (node-form node)))
(if (pair? form)
(map node->type form)
(desyntaxify form)))
(desyntaxify node)))
(define-reconstructor 'define syntax-type
(lambda (node constrained want-type)
':definition))
(define-reconstructor 'lap syntax-type
(lambda (node constrained want-type)
any-procedure-type))
(define name-node? (node-predicate 'name 'leaf))
(define lambda-node? (node-predicate 'lambda syntax-type))
(define literal-node? (node-predicate 'literal 'leaf))
; --------------------
; Primops.
;
; Most primops just have the types assigned in comp-prim.scm.
(define primop-reconstructors (make-symbol-table))
(define (define-primop-reconstructor name proc)
(table-set! primop-reconstructors name proc))
(define-reconstructor 'primitive-procedure syntax-type
(lambda (node constrained want-type)
(primop-type (get-primop (cadr (node-form node))))))
(define-primop-reconstructor 'values
(lambda (args constrained want-type)
(make-some-values-type (map (lambda (node)
(meet-type
(reconstruct node constrained value-type)
value-type))
args))))
(define-primop-reconstructor 'call-with-values
(lambda (args constrained want-type)
(if (= (length args) 2)
(let ((thunk-type (reconstruct (car args)
constrained
(procedure-type empty-rail-type
any-values-type
#f))))
(careful-codomain
(reconstruct (cadr args)
constrained
(procedure-type (careful-codomain thunk-type)
any-values-type
#f))))
error-type)))
(define (reconstruct-apply args constrained want-type)
(if (not (null? args))
(let ((proc-type (reconstruct (car args)
constrained
any-procedure-type)))
(for-each (lambda (arg) (examine arg constrained value-type))
(cdr args))
(careful-codomain proc-type))
error-type))
(define-primop-reconstructor 'apply reconstruct-apply)
(define-primop-reconstructor 'primitive-catch reconstruct-apply)
(define (constant-type x)
(cond ((number? x)
(meet-type (if (exact? x) exact-type inexact-type)
(cond ((integer? x) integer-type)
((rational? x) rational-type)
((real? x) real-type)
((complex? x) complex-type)
(else number-type))))
((boolean? x) boolean-type)
((pair? x) pair-type)
((string? x) string-type)
((char? x) char-type)
((null? x) null-type)
((symbol? x) symbol-type)
((vector? x) vector-type)
(else value-type)))
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