The Axiom interpreter is not able to parse the following statement:

[i for i in -1.0..0.0 by 0.5]

   The lower bound in a loop must be an integer.

But this has an obvious and useful interpretation so it is not clear why "lower bound in a loop must be an integer".

This is not a restriction that needs to be imposed on the Axiom library. See for example:

http://wiki.axiom-developer.org/SandBoxFloatSegment