Re: Questions about behavior observed in gm2

[Eric Streit]

hi,

I'm in the same state : I wrote a lot of programs in JPI Modula2, 30 
years ago.

I try to get back to Modula2 programming, but it's not easy (under Linux)

Answer to your first question : (in gm2.pdf )

-findexgenerate code to check whether array index values are out of 
bounds. Array
index checking can be disabled via ‘-fno-index’.


Eric


On 04/12/2023 07:22, Benjamin Kowarsch wrote:
> Welcome back to Modula-2
>
> On Mon, 4 Dec 2023 at 14:49, Jack Perry wrote:
>
>
>     I would be very grateful for any insight people can give on these;
>     I'm pretty sure they're easy to answer!
>
>     1. If I define the type `Constraints = [1..140]` and the variable
>     `Idx: Constraints`, then if I increment `Idx` repeatedly until `Idx
>     = MAX(Constraints) + 1`, should that be a run-time error? It is in
>     Ada, but not in Modula-2 w/gm2.
>
>
> It should cause a runtime fault in Modula-2 as well. However, some 
> compilers permit such runtime checks to be turned on and off by compiler 
> switches and if the default is 'off' it would have to be explicitly 
> turned on. I am not sure what the intended default behaviour in GM2 is. 
> Gaius (the developer of GM2) can clarify this.
>
>     4. There's no way to obtain a subscript of an array by "slicing", is
>     there? For example,
>
>            VAR
>               A: ARRAY [1..10] OF CHAR;
>           BEGIN
>               DoSomethignWith(A[3..5]);
>
>
> Array slicing is not a feature in PIM2/3/4 and ISO M2.
>
> FYI, it is a feature in M2 R10 though.
>
> array[n..m]  yields slice with elements of indices n to m
> array[n..-1]  yields slice with element of index n to last element
> array[n..-2]  yields slice with element of index n to second last element
> etc
>
> https://github.com/m2sf/m2bsk/wiki/Language-Specification-(7)-:- 
> Operators-and-Expressions#designation-operations <https://github.com/ 
> m2sf/m2bsk/wiki/Language-Specification-(7)-:-Operators-and- 
> Expressions#designation-operations>
>
> There's also insertion and concatenation.
>
> array[n..] := { foo, bar, baz }  inserts elements foo, bar and baz at 
> index n
> array1 & array2  yields concatenation product of array1 and array2
>
> https://github.com/m2sf/m2bsk/wiki/Language-Specification-(7)-:- 
> Operators-and-Expressions#collection-operations <https://github.com/ 
> m2sf/m2bsk/wiki/Language-Specification-(7)-:-Operators-and- 
> Expressions#collection-operations>
>
> Unfortunately though, the compiler is still work in progress and whilst 
> Gaius had expressed his intent for support in GM2 before, this hasn't 
> come to fruition yet either. I hope to find some time again working on 
> the compiler in the coming year. Eventually we'll get there, but for now 
> there is no array slicing in any working M2 compiler.
>
> regards
> benjamin (who is now rather busy running an artisan bakery)