Re: [Axiom-developer] Cleaning issues

[Ralf Hemmecke]

On 05/27/2007 04:34 AM, Gabriel Dos Reis wrote:
> Waldek Hebisch <address@hidden> writes:
>
> | I have looked at older issues in Issue Tracker and it seems that
> | there are significant number of issues which are just users not
> | understanding what Axiom is doing and expecting different result.
> | 
> | For example issue 165 the user clearly do not understand that
> | that Axiom blindly performs specified computations and that
> | 
> |   [j for j in 4.. | j < 10 ]
> | 
> | simply is an infinite loop.
>
> This one is indeed "paradoxical" at first sight, but is indeed
> an infinite computation.  What can we do about it? 
> Fo course we can tell user that he/she does not understand.
> Can we help with warnings from the interpreter or compiler?  Maybe we
> should. 

If an (optional) warning can be issued that would certainly be helpful. 
But one might run into that problem als in a .spad file.

Waldek, I wouldn't close that issue. The Axiom book should clearly state 
that a user might fall into this trap and at least give an example that 
the user probably meant.

  [j for j in 4.. while j < 10]

or

  [j for j in 4..9]

> | Simiarly 335 sort! drops list elements is just example of
> | linked list.  Something like:
> | 
> | (1) -> bb := [3, 4, 1, 2]
> | 
> |    (1)  [3,4,1,2]
> |                                                    Type: List PositiveInteger
> | (2) -> bs := sort! bb
> | 
> |    (2)  [1,2,3,4]
> |                                                    Type: List PositiveInteger
> | (3) -> bb

In Aldor one is told that if you use bang functions (i.e. functions that 
end in ! which are meant to be destructive on one of their arguments) 
you should be very very careful. In fact, you should never use the 
argument that you just destroyed. If a user still uses bb, it is *his* 
fault.

I know that that sounds a little too much for a beginner, but it is a 
simple rule. "Take care when you are using bang functions, you might 
introduce an explosion."

Ralf