The catalogue of examples
Every example program in flang lives in one directory — examples/: 190 files in twenty-one sets and one full-size project. There is no second directory of examples in the repository: until 24 August 2026 a hundred and fifty programs stood a floor below, and they could not be found at a glance.
The number is recounted by one command: git ls-files examples | grep -c '\.flang$' → 190 (measured 29 August 2026).
The sets
| Directory | .flang files | About what |
|---|---|---|
leetcode/ | 82 | solutions to LeetCode problems; every file is self-contained on purpose — why, is said in index.json. The account of this set is 82 problems |
rosetta/ | 28 | the canonical Rosetta Code tasks |
cat/ | 12 | category theory on applied problems: arrows with promises of their own, laws, CRDT merge |
web/ | 13 | HTTP: an orders service, the URL shortener and a marketplace API of three services — catalogue, cart, orders |
io/ | 8 | I/O orders: a binary file there and back, octets over the wire, a child process, an HTTPS request, a temporary directory, parsing a packet |
crypto/ | 8 | AES, ECDSA, X25519, X.509, a revocation list, a TLS hello — on real test vectors that lie next to them |
library-api/ | 7 | the domain half of a library REST service: lending, catalogue, fines. The only set that shows a project layout in full |
db/ | 4 | talking to PostgreSQL (SCRAM included), to Redis, and reading an SQLite file |
service-on-processes/ | 4 | a service on processes rather than on a three-function example: the claim about an own alternative to OTP, checked at full size |
https/ | 3 | TLS: the RFC 8448 records, the system trust store, a hello to a real host |
proof-probes/ | 3 | probes of the proof core itself: the typed-AST door, a refused generic descent, a variant with fields |
driver/ | 2 | hardware drivers where every function must provably terminate: a UART and an MSI |
measure/ | 3 | termination by a declared measure: Euclid, binary search, natural numbers |
errors/ | 2 | failure as a value rather than a crash: summing a column of numbers that arrived as strings, parsing numbers |
surfaces/ | 2 | factorial on the Chinese and the Esperanto surface of the language |
wal/ | 2 | a write-ahead log: parsing, printing, recovery after a truncation |
monad/ | 1 | an order total written in the в монаде form |
money/ | 1 | money on the exact decimal type сотых |
paths/ | 1 | the shortest path over a network with unreachable nodes |
allocator/ | 1 | a memory allocator as a pure automaton: can malloc be written in flang, and what does the kernel take about it |
host-boundary/ | 1 | the seam: flang decides, a C host executes — printed to C, built with the system cc, run whole |
service/ | 1 | asking a service |
import-check.flang | 1 | a probe of linking modules by name |
How to run them
Examples are declared inside functions rather than in separate check files, and they are run by the binary:
bootstrap/flang test examples/rosetta/ # one set
bootstrap/flang test examples/ # the whole catalogue, 190 filesThe sets cost very different amounts, and that is worth knowing before you start. The run of 24 August 2026: leetcode — 82 files, 804 examples, 12 seconds (that set holds 806 examples today); crypto — 8 files, 1223 examples, 39 minutes, because it computes real AES and ECDSA test vectors. A file the binary did not accept is named together with the refusal code rather than skipped in silence.
About library-api
library-api stands apart in this row, and that is the only thing in which the sets here differ from one another. The other twenty-one are programs: a file with declarations that carry their own examples. library-api is a project: seven flang modules, one of them its own, with a directory layout of its own. The example shows not HTTP but a border: what moves into the language, where a piece of logic has a runnable example, and what stays with the host. The host here was on Node and was removed on 20 August 2026 together with the rest of the JavaScript scaffolding; the flang half remained and is checked by a command. The rules drawn from this layout are collected in the repository layout.
Where to go next
- How to learn the language further — a reading order in which the examples are the fourth step;
- A study of 82 leetcode problems — what proved out on live code and what did not;
- The URL shortener and an application in the browser — two programs taken apart in full.