store: 'with-store' expands to a single procedure call.

* guix/store.scm (call-with-store): New procedure.
(with-store): Write in terms of 'call-with-store'.

guix/store.scm

@@ -602,19 +602,23 @@ connection.  Use with care."
   "Close the connection to SERVER."
   (close (store-connection-socket server)))
 
-(define-syntax-rule (with-store store exp ...)
+(define (call-with-store proc)
-  "Bind STORE to an open connection to the store and evaluate EXPs;
+  "Call PROC with an open store connection."
-automatically close the store when the dynamic extent of EXP is left."
   (let ((store (open-connection)))
     (dynamic-wind
       (const #f)
       (lambda ()
         (parameterize ((current-store-protocol-version
                         (store-connection-version store)))
-         exp) ...)
+          (proc store)))
       (lambda ()
         (false-if-exception (close-connection store))))))
 
+(define-syntax-rule (with-store store exp ...)
+  "Bind STORE to an open connection to the store and evaluate EXPs;
+automatically close the store when the dynamic extent of EXP is left."
+  (call-with-store (lambda (store) exp ...)))
+
 (define current-store-protocol-version
   ;; Protocol version of the store currently used.  XXX: This is a hack to
   ;; communicate the protocol version to the build output port.  It's a hack