Hi Alexander,
Your solution is a little more in the functional style than what I did
(below). Compared to mine it changes the semantics from a stand-alone
statement to an expression returning a value, but that really is not a
significant difference. I do like that it encapsulates the definition
of the error return variable.
Thanks,
George
(define-syntax with-database-connection
(syntax-rules ()
((with-database-connection conn err body ...)
; -- start template
(let/ec fail-network
(with-handlers [
(exn:fail:network?
(lambda (e)
(set! err "database connection error")
(fail-network)))
]
(let [
(conn (connect-database))
(sql-cmd #f)
]
(let/ec fail-sql
(with-handlers [
(exn:fail:sql?
(lambda (e)
(let [(info (exn:fail:sql-info e))]
(set! err (cdr (assoc 'message info)))
(fail-sql))))
]
(call-with-transaction conn
(lambda ()
body ...
)
#:isolation 'repeatable-read)
)
(disconnect conn))
)))
; -- end template
)))
On 12/8/2014 9:12 PM, Alexander D. Knauth wrote:
Sorry I missed this:
On Dec 8, 2014, at 6:45 PM, George Neuner <[email protected]
<mailto:[email protected]>> wrote:
and code in the <body> needs to reference “db"
(define (boiler-plate/f f)
(define err-msg #f)
(let/ec fail-network
(with-handlers ([exn:fail:network?
(lambda (e)
(set! err-msg "database connection error")
(fail-network err-msg))])
(let ([db (connect-database)])
(define (thunk)
(f db))
(let/ec fail-sql
(with-handlers ([exn:fail:sql?
(lambda (e)
(let ([info (exn:fail:sql-info e)])
(set! err-msg (cdr (assoc 'message info)))
(fail-sql err-msg)))])
(call-with-transaction db thunk #:isolation 'repeatable-read))
(disconnect db)
err-msg)))))
(define-syntax-rule (boiler-plate db body ...)
(boiler-plate/f (λ (db) body ...)))
(let ()
(define err-msg
(boiler-plate
db
< body ... >
))
; err-msg needed here
err-msg
)
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