Re: [Chicken-users] Request for comments on the SQLite3 egg API

[Ivan Shmakov]

> > > > > John Cowan <address@hidden> writes:

>> 1. Introduce a new separate singleton type for SQL NULL values and
>> refrain from using booleans altogether, because there is no SQL
>> boolean type in SQLite3.

> I favor a variant of this: introduce a singleton type for SQL NULL
> values, and map #t and #f inbound to 1 and 0 respectively (but not
> outbound, of course).  Ideally, the singleton type would be the same
> in all SQL eggs rather than SQLite-specific: one could use the symbol
> sql:null or even the empty list, which some people already pronounce
> "nil".

       I'd rather like it be a type disjoint from all the other Scheme
       types.

       May we have a library to implement SQL-like ternary logic as
       well?  E. g.:

;; Ivan Shmakov, 2007
;; Public domain

(require-extension syntax-case)

(define-record-type :sql-null
 (sql-null)
 sql-null?)

(define (sql-not o)
 (if (not (sql-null? o))
     (not o)
     o))

(define-syntax sql-or
 (syntax-rules ()
   ((sql-or)   #f)
   ((sql-or a)  a)
   ((sql-or a b ...)
    (if (or (sql-null? a) (not a))
        (sql-or b ...)
        a))))

(define-syntax sql-and
 (syntax-rules ()
   ((sql-and)   #t)
   ((sql-and a)  a)
   ((sql-and a b ...)
    (if (and a (not (sql-null? a)))
        (sql-and b ...)
        a))))

;; (sql-not (sql-null))         => SQL NULL ;
;; (sql-or  (sql-null) 1)       => 1 ;
;; (sql-or  (sql-null) #f)      => SQL NULL ;
;; (sql-and (sql-null) 1)       => SQL NULL ;

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