I guess
1) the "by 2" should not be ignored.
2) "2.. by 2" should be counted as a correct expression for a
UniversalSegment.
```
(12) -> l := [a,b,c,d,e,f,g,h,i,j]
(12) [a, b, c, d, e, f, g, h, i, j]
Type:
List(OrderedVariableList([a,b,c,d,e,f,g,h,i,j]))
(15) -> l(2..7)
(15) [b, c, d, e, f, g]
Type:
List(OrderedVariableList([a,b,c,d,e,f,g,h,i,j]))
(16) -> l(2..7 by 2)
(16) [b, c, d, e, f, g]
Type:
List(OrderedVariableList([a,b,c,d,e,f,g,h,i,j]))
(17) -> l(2.. by 2)
There are no library operations named BY having 1 argument(s) though
there are 1 exposed operation(s) and 0 unexposed operation(s)
having a different number of arguments. Use HyperDoc Browse, or
issue
)what op BY
to learn what operations contain " BY " in their names, or issue
)display op BY
to learn more about the available operations.
Cannot find a definition or applicable library operation named BY
with argument type(s)
PositiveInteger
Perhaps you should use "@" to indicate the required return type,
or "$" to specify which version of the function you need.
(17) -> l((2..) by 2)
(17) [b, c, d, e, f, g, h, i, j]
Type:
List(OrderedVariableList([a,b,c,d,e,f,g,h,i,j]))
```
Clearly, the problem lies here
https://github.com/fricas/fricas/blob/master/src/algebra/aggcat.spad#L1658
```
elt(x : %, i : UniversalSegment(Integer)) ==
l := low(i) - minIndex x
l < 0 => error "index out of range"
not hasHi i => copy(rest(x, l::NonNegativeInteger))
(h := high(i) - minIndex x) < l => empty()
first(rest(x, l::NonNegativeInteger), (h - l +
1)::NonNegativeInteger)
```
However, it is not so clear how the stepsize can be taken into account,
given that a generic implementation should work for finite (List) and
infinite (Stream) structures.
The same applies for the delete function.
Should we rather move that function into the respective domains and
implement it properly there? Or explicitly forbid (in the ++ docstrng
the "by n" in the UniversalSegment?
Ralf
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