Error message <corrupted statement> when using [i,j] with invalid indices

[ssiccha]

In GAP 4.9.1 and in the current master branch I get:

gap> l := [[1]];
[ [ 1 ] ]
gap> f := {} -> l[2,1];
function(  ) ... end
gap> f();
Error, List Element: <list>[2] must have an assigned value in
  return m[i][j]; at /home/sergio/projects/gap-master/lib/matrix.gi:30 called from 
<corrupted statement>  called from
<function "f">( <arguments> )
 called from read-eval loop at *stdin*:3
you can 'return;' after assigning a value
brk> 

Is it worth the effort to let GAP show the line from where the offending l[2,1] was called?

[stevelinton]

It's easy to fix this problem -- Just add SET_BRK_CALL_TO( expr) in EvalElm2List much as it appears in ElmList, and it seems to work correctly.

However, when I starting looking through related functions, though like EvalElmsList and EvalAss2List I become confused about where SET_BRK_CURR_STAT and SET_BRK_CALL_TO ought to appear and why. Does anyone understand the rules for these? If so, any chance of writing something about them (perhaps as comments vars.h where they are defined?

[ChrisJefferson]

I did look at this at some point, and got confused. I think @fingolfin was looking too, not sure how confused he got. This might require a sit down at a gap days to decide what we want, once and for all :)

[stevelinton]

It looks like PR #2520 is WIP on tackling this.

[fingolfin]

I'll take care of this as part of PR #2520 (or some successor PR)