todo.tag-counts

How many todos carry each tag, for a tag sidebar: most used first, open todos only unless asked.

1.0.0 · published 2026-10-03 by charlie · Anterra

Pinned by 10 tests, run in TypeScript, Python and Rust.

What it does

How many todos carry each tag, for a tag sidebar or filter chips: a list of `{ tag, count }`, most used first, ties in tag order (code point, via collections.sort-by, so `b-2`, `b10`, `b2`, not natural-number order).

- With `includeDone` false only open todos count, so the sidebar shows what is left to do; a tag whose todos are all done is left out rather than listed with a zero. - A todo counts once per tag, even if its tag list repeats one. - Tags are counted as stored. todo.item keeps them normalised (todo.normalise-tags), so `home` and `#Home` are already one tag.

For example

tagCounts(todos ×6, false) → ×3 open todos only: ties go alphabetically
tagCounts(todos ×6, true) → ×4 including done todos adds bills and more home and work
tagCounts(, true) → an empty list has no tags

The function

The same function in TypeScript, Python and Rust, pinned by the same tests. Pick your language; the choice follows you around the registry.

export function tagCounts(todos: readonly Todo[], includeDone: boolean): readonly TagCount[]

todos	Todo[]
includeDone	bool	false counts only open todos
returns	TagCount[]	count descending, then tag ascending; no zero counts

The type it declares, generated into your project

/** One tag and how many todos carry it. */
export interface TagCount {
  readonly tag: string;
  readonly count: number;
}

Your code names it in one line, in the file that uses it

import { tagCounts } from "#fune/todo.tag-counts@^1";

impl/typescript.ts · 20 lines · open · raw

Imports name this capability’s declared dependencies, which fune builds next to it in your project; each one links to its page.

import { sortBy } from "./collections_sort_by.ts";  ← from collections.sort-by ^1.0.0 · built alongside by fune
import { type Todo } from "./todo_item.ts";  ← from todo.item ^1.0.0 · built alongside by fune
import { type TagCount } from "./todo_tag_counts_types.ts";

/**
 * How many todos carry each tag, for a tag sidebar. A todo counts once per tag
 * even if its list repeats one. With includeDone false only open todos count,
 * so a tag whose todos are all done disappears. Most used first, then by tag
 * in code-point order (collections.sort-by, so every language agrees).
 */
export function tagCounts(todos: readonly Todo[], includeDone: boolean): readonly TagCount[] {
  const counts = new Map<string, number>();
  for (const todo of todos) {
    if (todo.done && !includeDone) continue;
    for (const tag of new Set(todo.tags)) counts.set(tag, (counts.get(tag) ?? 0) + 1);
  }
  const rows = [...counts].map(([tag, count]) => ({ tag, count }));
  const sorted = sortBy(sortBy(rows, "tag", "asc"), "count", "desc");
  return sorted.map((r) => ({ tag: r.tag as string, count: r.count as number }));
}

Install

fune build

With that line in your source, in a TypeScript project (language typescript in fune.project), fune build resolves it and its 2 dependencies, pins them in fune.lock, downloads only the TypeScript package of each, and builds the code above into your project’s .fune/build, one readable file per capability with a header linking back here. Or pin a range in fune.project and build in one step:

fune add todo.tag-counts

Download for TypeScript todo.tag-counts-1.0.0-typescript.fune · 10,632 bytes sha256 ae731054869b7a852554895db445417cc415e1af55411c5d14736876575748eb

The manifest, vectors and README with only the TypeScript implementation. Install it without the registry with fune add ./todo.tag-counts-1.0.0-typescript.fune, or fetch it from a terminal with fune pull todo.tag-counts@1.0.0:typescript.

The whole function, every language, is one file too: todo.tag-counts-1.0.0.fune, 13,164 bytes, sha256 3666265c41bbbb558c4084744eea9703df9e92cb87e8831c6fd0e5f1d8e56185. It installs into a project of any language.

Customise it in your app

The seams this capability offers. Put a marker directly above a function of your own and fune build wires it into the built code; the package on the registry is not changed, the built file’s header lists it under CUSTOMISED, and fune hooks lists every hook in the project. How hooks work.

before — your function gets the arguments and returns them, changed or not, or throws to refuse the call.

// fune: before todo.tag-counts

after — your function gets the result and the arguments, and returns the final result.

// fune: after todo.tag-counts

replace — inside this capability’s code only, calls to a dependency go to your function, with the same signature. Other capabilities that use it are unaffected; write in * to replace it everywhere.

// fune: replace collections.sort-by in todo.tag-counts
// fune: replace todo.item in todo.tag-counts

step — your function runs at a numbered point inside the function’s body, receives the in-scope values it names as parameters, and may return replacements. List the points with fune show todo.tag-counts --steps.

// fune: step todo.tag-counts after <n|label>

Tests

A version published now needs at least 8 tests for every function, and one that expects the error for each function that throws; the registry refuses it otherwise. fune verify --all runs each case in TypeScript, Python and Rust, and a project runs them again with fune verify. This page lists the cases; it does not run them. The exact JSON is vectors.json.

Case	Arguments		Expected
open todos only: ties go alphabetically	todos ×6, false	→	×3
including done todos adds bills and more home and work	todos ×6, true	→	×4
an empty list has no tags	, true	→
tags only on done todos are left out, not counted as zero	todos ×2, false	→
todos without tags	todos ×2, true	→
a tag repeated on one todo counts once	todos ×1, true	→	×1
ties are code-point order, not natural order: b-2, b10, b2	todos ×1, false	→	×4
count beats alphabet	todos ×3, false	→	×2
one todo's tags come out alphabetically, not in its own order	todos ×1, false	→	×2
a done todo counts when asked	todos ×1, true	→	×1

Files

Path	Bytes
README.md	601
impl/python.py	775
impl/rust.rs	1,632
impl/typescript.ts	1,000
vectors.json	6,278