Re: [Bug-apl] Error handling and IO

[Juergen Sauermann]

Hi Kacper et al, I understand. But I would say that using ⎕EA as you describe is exactly how cleanup should be done. I see ⎕EA not like (as the name may suggest) a means of trying different paths until one succeeds like in: 'try_A' ⎕EA 'try_B' ⎕EA 'try_C' ... but rather as: 'cleanup_failed_B' ⎕EA 'try_B' I also don;t see a good way of introducing a defer function without introducing a dubious APL syntax extension that would be difficult to read for people not knowing the extended syntax. For the sake of compatibility, such things should, IMHO, be avoided. /// Jürgen On 04/12/2016 02:10 AM, Kacper Gutowski wrote: If I understand correctly, Elias wants to have something that would ensure that every file opened is eventually closed (only more general so it can be applied to any external resources not only files). That is in a code similar to the following, to ensure the line 3 is always run even if there's an error in FUN. [1] FD←⎕FIO[3]STH [2] FUN FD [3] ⎕FIO[4]FD This can be ensured by wrapping FUN call with ⎕EA or ⎕EC. They return to the caller instead of suspending execution if error happens and this is correct and expected behaviour. But the intention is to have the file closed, not making the function unsuspendable, so this would be a side effect of the solution of using ⎕EA rather than the intended behaviour. But this doesn't mean there's anything wrong with ⎕EA or ⎕EC, of course. My understanding is that requested is some way to associate some kind of clean up code with )SI entry that would be run upon that entry being cleared from )SI regardless of how that happens. The way I imagine it, it could look like this (using an imaginary function ‘defer’ with a name borrowed from Golang; not an actual transcript): ∇ FOO [1] FD←⎕FIO[3]STH [2] defer '⎕FIO[4]FD' [3] FUN FD [4] other stuff ∇ STH←'filename' ⎕FX 'FUN F' '1+' FOO SYNTAX ERROR FUN[1] 1+ ^^ ⍝ here situation can be examined )VARS F FD )SIS FUN[1] 1+ ^^ FOO[3] FUN FD ^ ⋆ FOO ^ → ⍝ here ⎕FIO[4]FD is executed -k