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Further improvements for TR's error messages.

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Only the most permissive domains whose associated return type is
consistent with the expected type are shown in error messages.

For example, for a function with the following type:
Fixnum -> Fixnum
Integer -> Integer
and an expected type of Integer, only the latter domain is shown in
the error message.
This commit is contained in:
Vincent St-Amour 2010-09-24 17:43:12 -04:00
parent d6684dad8c
commit e011ea00bd
1 changed files with 88 additions and 34 deletions
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98
collects/typed-scheme/typecheck/tc-app-helper.rkt
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@ -88,6 +88,15 @@
;; unrelated to error reporting)
;; - if we have an expected type, we don't need to show the domains for which
;; the result type is not a subtype of the expected type
;; - we can disregard domains that are more restricted than required to get
;; the expected type (or all but the most liberal domain when no type is
;; expected)
;; ex: if we have the 2 following possible domains for an operator:
;; Fixnum -> Fixnum
;; Integer -> Integer
;; and an expected type of Integer for the result of the application,
;; we can disregard the Fixnum domain since it imposes a restriction that
;; is not necessary to get the expected type
(define (possible-domains doms rests drests rngs expected)
;; is fun-ty subsumed by a function type in others?
@ -103,7 +112,6 @@
(define expected-ty (and expected (match expected [(tc-result1: t) t])))
(define (returns-subtype-of-expected? fun-ty)
(and fun-ty ; was not skipped by a previous check
(or (not expected)
(match fun-ty
[(Function: (list (arr: _ rng _ _ _)))
@ -112,39 +120,85 @@
t]
[(ValuesDots: (list (Result: t _ _)) _ _)
t])])
(subtype rng expected-ty))]))))
(subtype rng expected-ty))])))
;; original info that the error message would have used
;; kept in case we discard all the cases
(define orig (map list doms rngs rests drests))
;; iterate in lock step over the function types we analyze and the parts
;; that we will need to print the error message, to make sure we throw
;; away cases consistently
(let loop ([cases (map (compose make-Function list make-arr)
doms
(map (lambda (rng) ; strip filters
(match rng
(map (match-lambda ; strip filters
[(Values: (list (Result: t _ _) ...))
(-values t)]
[(ValuesDots: (list (Result: t _ _) ...) _ _)
(-values t)]))
(-values t)])
rngs)
rests drests (make-list (length doms) null))]
[candidates '()])
;; the parts we'll need to print the error message
[parts orig]
;; accumulators
[candidates '()] ; from cases
[parts-acc '()]) ; from parts
;; discard subsumed cases (supertype modulo filters)
(if (not (null? cases))
;; discard subsumed cases
(let ([head (car cases)] [tail (cdr cases)])
(if (is-subsumed-in? head tail)
(loop tail (cons #f candidates)) ; will be skipped later
(loop tail (cons head candidates))))
(loop tail (cdr parts)
candidates parts-acc) ; we discard this one
(loop tail (cdr parts)
(cons head candidates) ; we keep this one
(cons (car parts) parts-acc))))
;; keep only the domains for which the associated function type
;; fits our criteria
(unzip4 (map cdr ; doms, rests drests
(let* ([orig (map list
(reverse candidates)
doms
rngs
rests
drests)]
[after (filter (compose returns-subtype-of-expected? car)
orig)])
;; if we somehow eliminate all the cases (bogus expected type)
;; fall back to the showing extra cases
(if (null? after) orig after)))))))
;; is consistent with the expected type
(let loop ([cases candidates]
[parts parts-acc]
;; accumulators
[candidates '()]
[parts-acc '()])
(if (not (null? cases))
(if (returns-subtype-of-expected? (car cases))
(loop (cdr cases) (cdr parts)
(cons (car cases) candidates) ; we keep this one
(cons (car parts) parts-acc))
(loop (cdr cases) (cdr parts)
candidates parts-acc)) ; we discard this one
;; among the domains that fit with the expected type, we only
;; need to keep the most liberal
;; since we only care about permissiveness of domains, we
;; reconstruct function types with a return type of any then test
;; for subtyping
(let ([fun-tys-ret-any
(map (match-lambda
[(Function: (list (arr: dom _ rest drest _)))
(make-Function (list (make-arr dom Univ rest drest null)))])
candidates)])
(let loop ([cases fun-tys-ret-any]
[parts parts-acc]
;; accumulators
;; final pass, we only need the parts to print the
;; error message
[parts-acc '()])
(if (not (null? cases))
;; if a case is a supertype of another, we discard it
(let ([head (car cases)])
(if (is-subsumed-in? head (remove head fun-tys-ret-any))
(loop (cdr cases) (cdr parts)
parts-acc) ; we discard this one
(loop (cdr cases) (cdr parts)
(cons (car parts) parts-acc)))) ; we keep this one
;; if we somehow eliminate all the cases (bogus expected
;; type) fall back to the showing extra cases
(unzip4 (if (null? parts-acc)
orig
(reverse parts-acc)))))))))))
(define (poly-fail t argtypes #:name [name #f] #:expected [expected #f])
(match t