Ctrl-A and Ctrl-X doing the opposite of what they should

Question

I had the following piece of Markdown text that I wanted to edit:

 * 2-6 for a moka pot
 * 7-10 for a drip machine
 * 5-12 for a pour-over

When I had the cursor over the number 6 in the first bullet point, pressing Ctrl-A should “Add [count] to the number or alphabetic character at or after the cursor”. Instead of giving 7, Vim decreased the number from 6 to 5. When I tried to decrease the number using Ctrl-X, it incremented instead. It was like both commands were doing the opposite of what they should.

I checked to see if some key-mapping was over-writing Vim’s defaults but running both :map <C-A> and :nmap <C-A> printed

No mapping found

Ditto for C-X. What’s going on?

Answer 1

Just use set nrformats+=unsigned. Then vim will treat all numbers as positive and ignore the hyphen.

Answer 2

It turns out that if a number is preceded by a hyphen-minus character (ASCII 45, 0x2D), Vim interprets the number as being a negative integer so Vim was actually adding +1 to -6, giving -5.

The solution was to replace the hyphens with en dashes to represent the range of values:

 * 2–6 for a moka pot
 * 7–10 for a drip machine
 * 5–12 for a pour-over

Note: Jason Diamond’s UniCycle plugin makes it easy to replace ASCII characters with typographically appropriate Unicode characters.