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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