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Re: [Bug-apl] Error handling and IO

From: Juergen Sauermann
Subject: Re: [Bug-apl] Error handling and IO
Date: Tue, 21 Jun 2016 16:57:11 +0200
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coming back to an earlier discussion, I have added ⎕EB ("Execute Both") to GNU APL.

A ⎕EB B is similiar to A ⎕EA B in that it first executes B. However, unlike
⎕EA which executes A only when B fails, ⎕EB always executes A regardless
of failures in B.

For example:

      '⎕←"CLEAN-UP"' ⎕EB '⍳4'
1 2 3 4

      '⎕←"CLEAN-UP"' ⎕EB '⍳4.5'
      '⎕←"CLEAN-UP"' μ-Z__A_Quad_EB_B '⍳4.5'
      ^                                    ^

SVN 750. All EOC stuff is gone now.

/// Jürgen

Elias Mårtenson <address@hidden> writes:
Yesterday, I participated in the Google Code Jam (programming competition). For one of the tasks,
APL was a very good fit. The question is here:

My solution (which I will not post right now, since one of you might want to give it a shot first) was terse
and simple. A very simple APL _expression_.

However, reading the input a file and formatting the result took many lines of very ugly code.

This attempt at using APL to solve a real-world programming problem illustrated two separate issues
that, needs to be handled:

Firstly, the FILE_IO library is way too low-level. For example, in the Codejam tasks, one usually have to
read a whitespace-limited sequence of numbers. When I solve the problems in Lisp, all I need to do is
to call READ. A flextible IO probrary that makes these kinds of this simple would be nice.

I could (and indeed have considered to) write such functions in APL, but this causes a second problem:

Error handling in GNU APL is very bad. In particular, there is nothing similar to UNWIND-PROTECT (or
try/finally in Java). There is no way to safely write code that opens a file, works on it and then closes it.
If an error occurs, there is no way to ensure that the filehandle is closed. When I developed my solution
to the Codejam problem, I ended up leaking a lot of file handles.

Does anyone know how Dyalog and other vendors handle this? Do they have a full exception system?



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