Re: [9fans] Inferno, Limbo unexpectancies

[forsyth@caldo.demon.co.uk]

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>>1 shadowing

shad.b:12: warning: redeclaration of local n, previously declared as a local on line shad.b:10

request warnings and you'll get them (-w option to limbo)

>>2 no bounds check in JIT

there's a plan to make them available in JIT mode as well.
(at least optionally: there are some things that can be proved
correct and don't need them but could use the speed.)

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To: 9fans@cse.psu.edu
Subject: [9fans] Inferno, Limbo unexpectancies
Date: Thu, 14 Feb 2002 16:05:15 +0100 (MET)
Message-ID: <200202141505.g1EF5FP01844@cbe.ericsson.se>

With the Inferno mail list down I hope to reach 'the right people' here at 
9fans.

If Inferno related emails are considered bandwith waisting, please let me know 
and I will stop.

I have stumbled upon 2 things in Limbo that I would like to warn about 
(presumably somebody else is as stupid as I am :-)


1 Unintended variable shadowing:

n := 3
while (n > 0) {
	n:= n - 1; # i know of n--, but this is an example
}


as is obvious (afterwards), n will never reach 0.
i really think the compiler should warn about this.



2 No array bounds checking (only for JIT):

The below program will crash at the return statement in crash(), not in the 
for() loop. Moreover, this only happens when using JIT.


bengt

implement Crash;

include "draw.m";
include "sys.m";
	sys: Sys;


Crash: module {
	init:	fn(nil: ref Draw->Context, args: list of string);
};

init(nil: ref Draw->Context, args: list of string) {
	sys = load Sys Sys->PATH;

	a:= crash(  );
	
	return;
}

crash(  ): array of byte {
	result:= array [1] of byte;

	for (i:= 0; i < 10; i++) {
		sys->print( "%d\n", i );
		result[i] = byte 0;
		sys->print( "%d\n", len result );
	}

	return result[:5];
}