I guess using 'from a known integer' could be slightly misleading since
the base type for the enum could be something other than an _int. I
would prefer the error to mention the enum in the text (I see its in the
error, but its at the front).
"expected a known _my-enum from C"
or something like that
On 11/16/2010 12:02 PM, John Clements wrote:
>
> 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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