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Show HN: I rewrote my notepad calculator as a local-first app with CRDT syncing (numpad.io)

46 points by tonyonodi ↗ HN
I launched NumPad v1 on here a few years ago, and back then it wasn't much more than a thin CodeMirror wrapper around the calculator engine I'd written.

Now I've rewritten it as a PWA that supports multiple documents, persists them to IndexedDB, and has a syncing service for paying customers. Syncing is handled by Automerge[1] under the hood, which should make it relatively easy to get document sharing working too.

[1] https://automerge.org/

20 comments

[ 3.6 ms ] story [ 57.3 ms ] thread
johncosta27
This is very cool. I was able to so some a small budget to see what my expenses are monthly, it's quite nice. I can see myself using it anytime I need something more than paper, and less than a full spreadsheet. Very cool.
[dead] eps
[flagged]
abfar
Nice tool, but the calculator executes division before exponentiation. E.g. 2^4/2 is evaluated to 4, not 8. However, it executes exponentiation first before multiplication (e.g. 2^2*3 is evaluated to 12). Is this intentional?
kragen
That's pretty nice; I've made a few attempts at such things myself, but the UI flow seems pretty smooth.

What's the license? I wouldn't want to use your code if copyright law poses a threat.

tonyonodi
It's closed source
kragen
Oh, okay, then I won't use it. Maybe it would have been better to say that up front instead of springing it on people later.
ajjenkins
This is really cool. I’m not sure what I would ever use it for, but it’s a cool idea and seems well executed.
justusthane
I don't mean this as a knock on OP, but it's not a new idea — I think the best known apps in this category are Soulver and Numi.

I find them super useful. Using natural language and storing the context along with the calculations helps me to sort of think through problems.

Being able to define variables on the fly is also very useful — I often use them for pricing out materials for projects. E.g.:

  "8ft 4 × 4" = $15
  "8ft 2 × 4" = $4
  "8ft 2 × 8" = $12
  "8ft 2 × 6" = $6.50
  "3/8in x 8in carriage bolt" = $3.50
  
  Adjustable stand
  "8ft 4 × 4" × 4
  "8ft 2 × 4" × 2
  "3/8in x 8in carriage bolt" × 12
  Plans $12
(What you can't see here is that Soulver gives all the totals in a bar on the right).

Soulver has some examples of other uses on their homepage: https://soulver.app

eviks
Unfortunately doesn't support superscripts 6²

Also is it possible to use CRDT as rich undo history, not only syncing?

tonyonodi
Yes it is, and it's on my roadmap.
zamadatix
Super clean style of interaction regarding the units and general syntax.

Regarding the CRDT side of things what's the main driver? Syncing is probably better off without CRDT (I'd rather know a note had 2 copies significantly edited differently and now I have a sync conflict rather than no sync conflict but a hacked up note) so I'm assuming paid customers get (or will soon get) live multi user editing (i.e. you can trade local for concurrent usage)

tonyonodi
Yes exactly, I had live multi-user editing as a feature until just before launch. In the end it needed a bit more work though, so I had to pull it.
shepik
The interface looks great.

Handling of "to" is a bit odd though.

150 kn in km/h [277.79976 kph] - this is unit convertion

150 kn to km/h [-276.79976 kph] - this is unexpectedly subtraction. I expected the unit conversion here, because of Raycast and Google

tonyonodi
Yeah, this was a deliberate decision, but a tough one and I can see why you might find it annoying. I think it makes date and time calculations more readable:

09:11 to 15:46

zuzzurro
How do I do get the right result when trying: 200Mbps * 2hours? I get "400 Mbits/s hr" and that's not what I'm looking for. It seems to be working if I use seconds instead. 200Mbps*2s=400 megabits
tonyonodi
`200 Mbps * 2 hours in Mb` the second one works because the derived unit of the calculation works out to be exactly the same as a megabit, but that's not the case for the first one so you have to convert manually.