make contract-stronger? recognize that predicates are stronger than

values that they accept (for certain, well-known predicates, anyway)

pkgs/racket-pkgs/racket-test/tests/racket/contract/stronger.rkt

@@ -128,6 +128,20 @@
       (define x (flat-rec-contract x (or/c (cons/c x '()) '())))
       (,test #t contract-stronger? x (or/c (cons/c x '()) '()))))
   
+  (ctest #t contract-stronger? "x" string?)
+  (ctest #f contract-stronger? string? "x")
+
+  (ctest #t contract-stronger? 1 real?)
+  (ctest #f contract-stronger? real? 1)
+
+  (ctest #t contract-stronger? 'x symbol?)
+  (ctest #f contract-stronger? symbol? 'x)
+  
+  ;; chances are, this predicate will accept "x", but
+  ;; we don't want to consider it stronger, since it 
+  ;; will not always accept "x".
+  (ctest #f contract-stronger? "x" (λ (x) (not (zero? (random 10000)))))
+
   (contract-eval
    `(let ()
       (define (non-zero? x) (not (zero? x)))

racket/collects/racket/contract/private/guts.rkt

@@ -5,9 +5,9 @@
          "prop.rkt"
          "rand.rkt"
          "generate-base.rkt"
-         racket/pretty)
-
-(require (for-syntax racket/base))
+         racket/pretty
+         (for-syntax racket/base
+                     "helpers.rkt"))
 
 (provide coerce-contract
          coerce-contracts
@@ -151,7 +151,7 @@
                             "contract?"
                             x)))
 
-;; coerce-contracts : symbols (listof any) -> (listof contract)
+;; coerce-contracts : symbol (listof any) -> (listof contract)
 ;; turns all of the arguments in 'xs' into contracts
 ;; the error messages assume that the function named by 'name'
 ;; got 'xs' as it argument directly
@@ -173,13 +173,20 @@
   (cond
     [(contract-struct? x) x]
     [(and (procedure? x) (procedure-arity-includes? x 1)) 
-     (make-predicate-contract (or (object-name x) '???) x #f)]
+     (make-predicate-contract (or (object-name x) '???) 
+                              x 
+                              #f 
+                              (memq x the-known-good-contracts))]
     [(or (symbol? x) (boolean? x) (char? x) (null? x) (keyword? x)) (make-eq-contract x)]
     [(or (bytes? x) (string? x)) (make-equal-contract x)]
     [(number? x) (make-=-contract x)]
     [(or (regexp? x) (byte-regexp? x)) (make-regexp/c x)]
     [else #f]))
 
+(define the-known-good-contracts
+  (let-syntax ([m (λ (x) #`(list #,@(known-good-contracts)))])
+    (m)))
+
 (struct wrapped-extra-arg-arrow (real-func extra-neg-party-argument)
   #:property prop:procedure 0)
 
@@ -300,8 +307,12 @@
      (λ (fuel) (λ () v)))
    #:stronger
    (λ (this that)
-      (and (eq-contract? that)
-           (eq? (eq-contract-val this) (eq-contract-val that))))))
+     (define this-val (eq-contract-val this))
+     (or (and (eq-contract? that)
+              (eq? this-val (eq-contract-val that)))
+         (and (predicate-contract? that)
+              (predicate-contract-sane? that)
+              ((predicate-contract-pred that) this-val))))))
 
 (define-struct equal-contract (val)
   #:property prop:custom-write custom-write-property-proc
@@ -311,8 +322,12 @@
    #:name (λ (ctc) (equal-contract-val ctc))
    #:stronger
    (λ (this that)
-      (and (equal-contract? that)
-           (equal? (equal-contract-val this) (equal-contract-val that))))
+     (define this-val (equal-contract-val this))
+     (or (and (equal-contract? that)
+              (equal? this-val (equal-contract-val that)))
+         (and (predicate-contract? that)
+              (predicate-contract-sane? that)
+              ((predicate-contract-pred that) this-val))))
    #:generate
    (λ (ctc) 
      (define v (equal-contract-val ctc))
@@ -326,8 +341,12 @@
    #:name (λ (ctc) (=-contract-val ctc))
    #:stronger
    (λ (this that)
-      (and (=-contract? that)
-           (= (=-contract-val this) (=-contract-val that))))
+     (define this-val (=-contract-val this))
+     (or (and (=-contract? that)
+              (= this-val (=-contract-val that)))
+         (and (predicate-contract? that)
+              (predicate-contract-sane? that)
+              ((predicate-contract-pred that) this-val))))
    #:generate
    (λ (ctc) 
      (define v (=-contract-val ctc))
@@ -349,7 +368,9 @@
       (and (regexp/c? that) (eq? (regexp/c-reg this) (regexp/c-reg that))))))
 
 
-(define-struct predicate-contract (name pred generate)
+;; sane? : boolean -- indicates if we know that the predicate is well behaved
+;; (for now, basically amounts to trusting primitive procedures)
+(define-struct predicate-contract (name pred generate sane?)
   #:property prop:custom-write custom-write-property-proc
   #:property prop:flat-contract
   (build-flat-contract-property
@@ -391,7 +412,7 @@
 (define (check-flat-named-contract predicate) (coerce-flat-contract 'flat-named-contract predicate))
 (define (check-flat-contract predicate) (coerce-flat-contract 'flat-contract predicate))
 (define (build-flat-contract name pred [generate #f])
-  (make-predicate-contract name pred generate))
+  (make-predicate-contract name pred generate #f))
 
 
 ;; Key used by the continuation mark that holds blame information for the current contract.

racket/collects/racket/contract/private/helpers.rkt

@@ -7,6 +7,7 @@
          add-name-prop
          all-but-last
          known-good-contract?
+         known-good-contracts
          update-loc)
 
 (require setup/main-collects
@@ -370,3 +371,7 @@
   (and (symbol? r-id)
        (hash-ref known-good-syms-ht r-id #f)
        (free-identifier=? id (datum->syntax #'here r-id))))
+
+(define (known-good-contracts)
+  (for/list ([(k v) (in-hash known-good-syms-ht)])
+    (datum->syntax #'here k)))

racket/collects/racket/contract/private/misc.rkt

@@ -1447,9 +1447,9 @@
   (cond
     [(and (procedure? predicate)
           (procedure-arity-includes? predicate 1))
-     (make-predicate-contract name predicate generate)]
+     (make-predicate-contract name predicate generate #f)]
     [(flat-contract? predicate)
-     (make-predicate-contract name (flat-contract-predicate predicate) generate)]
+     (make-predicate-contract name (flat-contract-predicate predicate) generate #f)]
     [else
      (raise-argument-error 'flat-named-contract
                            (format "~s" `(or/c flat-contract?