Allow stepped integer parameters.

[hjoliver]

[cylc]
   [[parameters]]
        idx = 1..9^2  # 1, 3, 5, 7, 9

[UPDATE: syntax changed to 1..9..2 below]

[hjoliver]

I can't recall if I had a reason for not assigning reviews on this 3 weeks ago 😬 - looks good to go, including documentation and tests. See what you think...

[matthewrmshin]

As a matter of interest, did you borrow this syntax from any language? (In both Perl and Python, the ^ operator appears to be the bitwise XOR operator.)

[hjoliver]

Nope, thought that might be a point of contention. We can't use comma, obviously.

[matthewrmshin]

In fact, the ^ operator appears to be the bitwise XOR operator in most languages derived from C. The only other thing I can think of is to use .. again in a ternary way, START..END[..STEP], e.g. 1..9..2.

[arjclark]

I think @matthewrmshin's solution makes sense as it's in line with what you'd expect from something like python's range(start, end, step=1) function.

[hjoliver]

Maybe... IMO .. is intuitive syntax for a range, but ideally we'd have something else for step. What about 1..9;2?

[arjclark]

Or how about 1:9:2?

[hjoliver]

Yeah, I could go for the colon.

[matthewrmshin]

The .. operator is a well known operator in various languages including Perl and Ruby, but none of them have thought about steps.

I don't like : or ; for the same reason as ^ - both are well known operators that mean something else.

[dvalters]

1..9..2 mimics bash, 1:9:2 is python slice style...I like either. Making up our own seems confusing possibly?

[oliver-sanders]

+1 for START..END..STEP. In python's slice syntax the end-point is excluded i.e. 1:9:2 = 1, 3, 5, 7, whereas in bash this is inclusive i.e. 1..9..2 = 1, 3, 5, 7, 9.

[matthewrmshin]

I suppose you can do:

REC_PARAM_INT_RANGE = re.compile('(\d+)\.\.(\d+)(?:\^(\d+))?')

to avoid capturing the 3rd bracket?

[oliver-sanders]

Looks good. Same comment from me about making the "junk" regex group non-capturing.

[matthewrmshin]

Hi @hjoliver Are you happy to settle for the START..END..STEP syntax?

[hjoliver]

@matthewrmshin - yes I'm happy, just crazy busy this week (sorry). (have started the big review btw, but not finished...)

[matthewrmshin]

(I'll merge after the CI test passes.)