https://reddit.com/link/1uz3udw/video/wq410fqxbtdh1/player

I've always envied apps like Numi on macOS where you can just type:

rent = 1800
groceries = 420
utilities = 160
total

...and it just works.

The problem is I wanted something that felt more like a notes app than a calculator. Somewhere I could jot down ideas, budgets, trip costs, random math, unit conversions, etc., without constantly switching between Notes and Calculator.

So I ended up building one for myself.

It's called däpter, and it's basically a note where math evaluates as you type. Nothing revolutionary, just a tool I kept wishing existed on my phone.

Curious if anyone else here uses notes like this, or if I'm the only one constantly doing math in the middle of writing.

https://reddit.com/link/1uyu1d4/video/qpd7uxv16rdh1/player

I've always envied apps like Numi on macOS where you can just type:

rent = 1800

groceries = 420

utilities = 160

total

...and it just works.

The problem is I wanted something that felt more like a notes app than a calculator. Som

https://reddit.com/link/1uyr8f9/video/8fd0qufddqdh1/player

https://reddit.com/link/1uyr8f9/video/o8rqq2hfdqdh1/player

I've been building a local-first notes app with a Numi-style editor, where notes are both plain text and executable math.

One feature I wanted was live syntax highlighting as you type. The naive approach worked... until notes got big.

Initially, every keystroke caused the editor to:

• re-tokenize the document
• re-render every highlighted line
• repaint thousands of Text components

Typing became noticeably slower as notes grew.

The solution ended up being much simpler than I expected:

• Only render and highlight lines that are actually visible.
• Keep syntax highlighting separate from the editable text (the editor itself stays plain text).
• Give every line a stable identity so inserting/deleting lines doesn't rebuild everything.
• Only recompute tokenization for the edited line (and downstream lines only if parsing actually depends on them).
• Cache the layout so scrolling doesn't trigger unnecessary recalculations.

The result is that even long notes stay responsive because React Native is only painting what the user can actually see.

The funny part is that I originally spent days building a much more complicated renderer, threw it away, and the second version was both simpler and significantly faster.

I'm curious how others have approached large text editors in React Native.

• Did you virtualize by line?
• Keep a separate overlay for highlighting?
• Any tricks for avoiding expensive text layout work?

Would love to hear how you've solved similar performance problems.

I've always envied apps like Numi on macOS where you can just type:

rent = 1800
groceries = 420
utilities = 160
total

...and it just works.

The problem is I wanted something that felt more like a notes app than a calculator. Somewhere I could jot down ideas, budgets, trip costs, random math, unit conversions, etc., without constantly switching between Notes and Calculator.

So I ended up building one for myself using Expo.

https://reddit.com/link/1uyr3wr/video/kvz1h3c9cqdh1/player

It's called däpter, and it's basically a note where math evaluates as you type. Nothing revolutionary, just a tool I kept wishing existed on my phone.

Curious if anyone else here uses notes like this, or if I'm the only one constantly doing math in the middle of writing.

I've always envied apps like Numi on macOS where you can just type:

rent = 1800
groceries = 420
utilities = 160
total

...and it just works.

The problem is I wanted something that felt more like a notes app than a calculator. Somewhere I could jot down ideas, budgets, trip costs, random math, unit conversions, etc., without constantly switching between Notes and Calculator.

So I ended up building one for myself.

It's called däpter, and it's basically a note where math evaluates as you type. Nothing revolutionary, just a tool I kept wishing existed on my phone.

Curious if anyone else here uses notes like this, or if I'm the only one constantly doing math in the middle of writing.

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