On Nov 15, 2010, at 3:02 PM, John Clements wrote: > The documentation for '_enum" says this: > > 3.8 Enumerations and Masks > > Although the constructors below are describes as procedures, they are > implemented as syntax, so that error messages can report a type name where > the syntactic context implies one. > > (_enum symbols [basetype]) → ctype? > symbols : list? > basetype : ctype? = _ufixint > Takes a list of symbols and generates an enumeration type. The enumeration > maps between a symbol in the given symbols list and corresponding integers, > counting from0. > The list symbols can also set the values of symbols by putting '= and an > exact integer after the symbol. For example, the list '(x y = 10 z) maps 'x > to 0, 'y to 10, and 'z to11. > > The basetype argument specifies the base type to use. > > > This says nothing about what happens when using racket->C on a symbol that's > not mentioned by the enumeration, or what happens when using C->racket on a > number that's not mentioned in the enumeration. > > Based on my tests, it appears that the conversion signals an error in the > racket->C direction, but simply returns #f in the C->racket direction. > > Should I document the current behavior, or would it make more sense to change > it to signal an error rather than returning #f?
Okay the existing behavior was bothering me because (post-conversion to #f)
there's no way to recover the problematic integer. I therefore changed it so
it signals an error instead, like this:
. . . plt/collects/racket/private/more-scheme.rkt:265:2: enum:int->_my-enum:
expected a known integer from C, got: 6
That error comes from linking to a file with this C function:
int tester(int x){
return x+2;
}
... using this racket program:
#lang racket
(require ffi/unsafe)
(define lib (ffi-lib "/tmp/tester.dylib"))
(define _my-enum
(_enum
'(chicken = 3
monkey = 4
duck = 5)))
(define tester
(get-ffi-obj "tester" lib (_fun _my-enum -> _my-enum)))
(tester 'monkey)
... and finally, here's the diff:
pcp062767pcs:~/plt/collects/ffi clements$ git diff unsafe.rkt
diff --git a/collects/ffi/unsafe.rkt b/collects/ffi/unsafe.rkt
index 66fd34a..99e0d7f 100644
--- a/collects/ffi/unsafe.rkt
+++ b/collects/ffi/unsafe.rkt
@@ -765,6 +765,8 @@
(define int->sym '())
(define s->c
(if name (string->symbol (format "enum:~a->int" name)) 'enum->int))
+ (define c->s
+ (if name (string->symbol (format "enum:int->~a" name)) 'int->enum))
(let loop ([i 0] [symbols symbols])
(unless (null? symbols)
(let-values ([(i rest)
@@ -784,7 +786,11 @@
(if a
(cdr a)
(raise-type-error s->c (format "~a" (or name "enum")) x))))
- (lambda (x) (cond [(assq x int->sym) => cdr] [else #f]))))
+ (lambda (x) (cond [(assq x int->sym) => cdr]
+ [else
+ (error c->s
+ "expected a known integer from C, got: ~s"
+ x)]))))
;; Macro wrapper -- no need for a name
(provide _enum)
Let me know if it's okay to commit this. If I don't hear back in a couple of
days, I'll just go ahead :).
John
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