[e-lang] lambda-args block ejectors: beginning or end?

[Kevin Reid]

Context: Mark Miller and I were discussing lambda-args yesterday, and  
I pointed out that the current expansion does not allow for the  
control object to handle match failures in the blocks' patterns.

At the time, we decided that each block function should have the  
first argument be an ejector.

? someControl () foo [x] [y] {}
# expansion: someControl."foo__control/0/2"(def _ {
#
#                method run() {
#                    __makeList.run(__makeList.run(), def _ {
#
#                        method run(ej__1, sp__1, sp__2) {
#                            def [x] exit ej__1 := sp__1
#                            def [y] exit ej__1 := sp__2
#                            null
#                        }
#                    })
#                }
#            }).run__control()

(After having implemented this, I'd like to propose the special case  
that if there are no parameters, there should be no ejector.)

However, in the case where the block has 1 parameter, this is the  
opposite of the common (specimen, ejector) argument order.

In particular, I was updating the control emakers to this expansion,  
and noticed that I could implement match failure in the 'escape'  
control object to match Kernel-E:

? escape f { f(1) } catch x :String { [x] }
# value: 1

in this way:

def flip(f) {
   return fn a, b { f(b, a) }
}

                     ...
                     to run__control() :any {
                         return escape ejector {
                             tryFn(null, ejector)
                         } catch via (flip(handlerFn)) value {
                             value
                         }
                     }

It would be nice if the 'flip' could be eliminated here.

-- 
Kevin Reid                            <http://homepage.mac.com/kpreid/>