lib/template: allow range over number

[phenpessoa]

This PR adds the ability to range over a number (i.e. ints and uints) in template.

{{range $k, $v := 2}}{{$k}}{{$v}}{{end}}

Should print 0011

{{range 2}}{{.}}{{end}}

Should print 01

{{range 0}}{{else}}empty{{end}}

Should print empty

{{range -1}}{{else}}empty{{end}}

Should throw an error

[jo3-l]

I would rather raise a runtime error in this case. WDYT?

[phenpessoa]

Sounds fine with me, but I think it might not be so user friendly if the value of n is a variable that the user does not know the value, like a count from DB
Perhaps < 0 could be a runtime error but = 0 could remain a simple break, WDYT?

[jo3-l]

I think range 0 should be permitted, but negative is nonsensical.

[phenpessoa]

Updated

[jo3-l]

ditto

[SoggySaussages]

Why is this necessary when we already have seq? You can get the same result in each of your examples by prefixing seq 0 to each number. This method saves 5 characters for each call, is that the only difference? Would this confuse users and devalue the existing function? Maybe I'm misunderstanding something here.

[phenpessoa]

It provides, imo, a better syntax. Also, it does not require allocating a slice, thus using less memory.
But yes, this PR is basically syntactic sugar.

Would this confuse users and devalue the existing function?

I don't think so. Seq still allows you to start from a value other than 0.

This PR is inspired on the proposal to range over n in go itself.