Re: [Chicken-users] define-foreign-enum-type

[John J Foerch]

I think I am beginning to understand.  Thank you.

John

Jim Ursetto <address@hidden> writes:
> define-foreign-enum-type also defines a bunch of other stuff that you are 
> skipping over
> in your version that compiles, such as garmonbozia->int conversions.  
> Specifically
> if you expand the macro you will find it expands to something like
>
> (define-foreign-type garmonbozia "garmonbozia")
> (define-foreign-variable pain "garmonbozia" "pain")
> (define (int->garmonbozia x)
>   (cond ((= x pain) 'pain)                 ;; this line fails to compile
>   ... etc. ...)
>
> The reason is Chicken cannot convert the reference to the C
> foreign variable pain to a Scheme value, because "garmonbozia"
> is not a valid Scheme foreign type.
>
> It works fine in the pointer case because you can pass
> around pointers to any foreign type (as it's just a
> C pointer, and Chicken doesn't have to do any conversion).
>
> Jim
>
>
> On Apr 26, 2012, at 9:40 PM, John J Foerch wrote:
>
>> Hello,
>> 
>> I am using chicken 4.7.0, and in the course of writing some library
>> bindings, I came upon a difference between define-foreign-type and
>> define-foreign-enum-type that puzzles me.  Here is a minimal program
>> that shows it:
>> 
>>    (import chicken scheme foreign foreigners)
>> 
>>    #>
>>    typedef enum {
>>        pain,
>>        suffering,
>>        fear
>>    } garmonbozia;
>> 
>>    void creepy_dream (garmonbozia *x) {
>>        printf("give me back my garmonbozia!\n");
>>        *x = fear;
>>    }
>>    <#
>> 
>>    ;;; this compiles:
>>    (define-foreign-type garmonbozia "garmonbozia")
>> 
>>    ;;; this does not:
>>    ;; (define-foreign-enum-type (garmonbozia "garmonbozia")
>>    ;;   (garmonbozia->int int->garmonbozia)
>>    ;;   pain suffering fear)
>> 
>>    (define (creepy-dream)
>>      (let-location ((a int))
>>        ((foreign-lambda void creepy_dream (c-pointer garmonbozia))
>>         (location a))
>>        a))
>> 
>>    (print (creepy-dream))
>> 
>> It compiles and works fine with the 'define-foreign-type' form, but if I
>> comment that one out, and uncomment the 'define-foreign-enum-type' form,
>> I get the following error:
>> 
>>    Error: illegal foreign return type `garmonbozia'
>> 
>>    Error: shell command terminated with non-zero exit status 256:
>>    /usr/bin/chicken enumpointer6.scm -output-file enumpointer6.c
>> 
>> Can somebody explain the difference?
>> 
>> Thank you,
>> 
>> -- 
>> John Foerch
>> 
>> 
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