Is your feature request related to a problem? Please describe.

The main module I encountered this to report by was battery, but I can see this as a helpful feature in general. I was getting frustrated at writing out the same bit of line 20 times in order to accomplish what I wanted. Eg, I currently have

ramp-capacity-0 = 
ramp-capacity-1 = 
ramp-capacity-2 = 
ramp-capacity-0-foreground = ${color.red}
ramp-capacity-1-foreground = ${color.yellow}
ramp-capacity-2-foreground = ${color.lgreen}

animation-charging-0 = 
animation-charging-1 = 
animation-charging-2 = 
animation-charging-0-foreground = ${color.blue}
animation-charging-1-foreground = ${color.blue}
animation-charging-2-foreground = ${color.blue}
animation-charging-framerate = 750

The effect I want to achieve is likely going to be that <= 5% should be red, 5 - 25 yellow, 25 - 85 green, and 85+ a different shade of green (the colors aren't support important, I'm still playing with them). The current status quo for ranges seems to be from issue #63 where we would have to define at least 20 different ramp capacities and each one's foreground color.

Why does polybar need this feature?

There are times when we have a lot of repetitive code that could've been written in exponentially shorter number of lines. In addition, it provides for more... dynamic code. Eg, the battery solution could be written as:

for i in range(5):
    ramp-capacity-$i$ = 
    ramp-capacity-0-foreground = ${color.red}
for i in range(5, 25):
    ramp-capacity-$i$ = 
    ramp-capacity-0-foreground = ${color.yellow}
for i in range(25, 85):
    ramp-capacity-$i$ = 
    ramp-capacity-0-foreground = ${color.lgreen}
for i in range(85, 100):
    ramp-capacity-$i$ = 
    ramp-capacity-0-foreground = ${color.green}

Now, we'd only have to change one line to change a whole range's values. (this could have been done with 2 loops admittedly for actually 20 ramps, but I did it for uniformity for the example)

Describe the solution you'd like

I discuss these in the other headings 🙃

Describe alternatives you've considered

The easiest solution would be to just write my statements out 20 times and use regex replaces. I've considered possibly a custom script, but that sort of defeats the purpose of various modules (like battery). My other solution was writing a python program or of the sort and having it output the lines we can replace. These are obviously less attractive than actual loop functionality.

Additional context

I realize this feature could be fatally flawed. It would be best to limit the loops to be for loops, iterating over only over ranges. A normal loop like for(int i = 0; i < 5; i++) or while loop could hold potential to have flawed logic and fail horribly (eg for(int i = 0; i > 5; i++)). These should probably be interpreted statically (ie if it makes sense that the loop creates 5 lines, then the loop always has those 5 lines, and not 10 in a different minute or something).