Hi,
HiPhish <[email protected]> skribis:
> Hello, it's me again, the guy who wants to implement MessagePack [1] in
> Guile.
> The specification defines a type of "extension" [2], a pair of an 8-bit
> integer and a byte array for data. Implementing this type as a record is
> obvious, but what should be the name of the constructor?
>
> (define-record-type ext
> (make-ext type data)
> ext?
> (type ext-type)
> (data ext-data))
>
> Either `make-ext` or just `ext` seem appropriate.
For immutable records (which should be the norm :-)), I often leave out
‘make-’ nowadays. (The analogy is ‘string’ vs. ‘make-string’, for
instance.)
> I have seen both types of constructors, what do you guys say? And
guys and gals :-)
> while I'm on the topic, what about types? An extension is only valid
> if the first field (type) is an integer from -128 to 127 and the data
> a vector of bytes (integer in the range from 0 to 255). How do I
> enforce this invariant without static typing?
You could enforce it by not exporting the raw record constructor, and
instead exporting a procedure that performs all the necessary checks:
(define-record-type <ext>
(%ext type data) ;private
ext?
…)
(define (ext type data) ;public
(assert-valid-arguments type data)
(%ext type data))
HTH!
Ludo’.
