A For-Next bug in 1.2.8-s682

[boriel]

This works:

Code:

For i = AttrAddress to AttrAddress + NumberOfCells - 1 Poke i, AttrColor Next i

This does not:

Code:

For AttrAddress = AttrAddress to AttrAddress + NumberOfCells - 1 Poke AttrAddress, AttrColor Next AttrAddress

This would work in other dialects.

Thanks,

Darkstar

This is related to the ZX Basic to have "Dynamic" evaluation on each pass. In your loop:

Code:

For i = i to i + N - 1 Poke i, AttrColor Next i

the expression i + N - 1 is evaluated *on each pass* (like in C). On most BASIC dialects (including Sinclair BASIC), that expression is only evaluated the 1st time (on entering the loop). On each pass, i + N - 1 is recalculated, and since it's always increasing, the loop will eventually overflow (or run forever).
At the moment, the only way to fix this is:

Code:

LET z = i + N - 1 For i = i to z Poke i, AttrColor Next i

Can you check this?

Which produces the expected behavior. I'm thinking in fixing this in an more efficient manner, so the user can choose dynamic or static FOR loops with a #pragma directive, and let FOR to be static by default for compatibility's sake. What do you think?