# Session summary — 2026-09-28 (b): Unicode, stdlib, language polish

Suite **128/128**; self-hosting fixpoint **OK**
(`bootstrap/fixpoint.sh`, image **2,080,607 bytes**). `master`, tree
clean except the user's uncommitted `compiler/toto.mod`.

This session continued from "V3 self-hosts (byte-identical fixpoint)"
and completed four workstreams, each its own tagged step. Every step
re-ran the fixpoint, so the compiler's own sources are compiled with
the new semantics each time.

## Steps, tags and headline commits

| Step | Tag | Commit | What |
| --- | --- | --- | --- |
| Unicode inc. 1 | `v3-unicode-1` | `af09dc6` | `UCHAR`, `U'..'`/`U".."` literals, strict RFC 3629 → 234, `UCHR`/`CHR8`/`UORD` |
| Unicode inc. 2 | `v3-unicode-2` | `f1bfd76` | `runtime/syslib/Utf8`, `TextIO.U*` UTF-8 output |
| stdlib | `v3-stdlib-conversions` | `2f80422` | `Conversions`, `RealIO` (+ shim real helpers) |
| session doc | `v3-unicode-stdlib-summary` | `810946b` | first consolidated summary |
| language | `v3-lang-polish` | `23e7bf3` | enum literals everywhere; string `=`/`#` |
| stdlib | `v3-programargs-iochan` | `4afc2b2` | `ProgramArgs`, `IOChan` (+ `SysShim` primitives) |
| showcase | `v3-showcase14`, `v3-showcase14-summary` | `94c4c5e` | end-to-end program linking 7 modules |
| language | `v3-strcat` | `259f5ac` | string `+`, content-copy assignment, `LEN` of literals |

## 1. Unicode (complete)

- `UCHAR`: 32-bit codepoint, a distinct type (QBE `w`).
- `U'..'`/`U".."` literals with strict RFC 3629 decoding
  (overlong/surrogate/`>10FFFF`/truncation → error
  **234 `invalid UTF-8 in U-literal`**). One codepoint → `UCHAR`;
  otherwise a **UString** descriptor `{ l count, w cp… }`, which is a
  valid V3 array for an open `ARRAY OF UCHAR` formal.
- `runtime/syslib/Utf8` (`Decode`/`Encode`); `TextIO.UWriteChar`/
  `UWriteString`/`UWriteLn` emit real UTF-8 (verified byte-for-byte).
- **Flagged deviations**: `UORD` returns `INTEGER` (V3 has no
  `LONGCARD` name and no 64→32-bit conversion); `UCHR` also accepts an
  integer operand; the front-end decode lives in `QbeGen.DeclUStr`
  (Stage 1 is gm2-built and cannot import a `UCHAR`-typed module).
- Docs: `docs/summary_unicode.md`.

## 2. Library

- **`Conversions`** — `IntToStr`/`CardToStr`/`RealToStr`,
  `StrToInt`/`StrToCard`/`StrToReal` (BOOLEAN results).
- **`RealIO`** — `WriteReal`/`WriteRealF`/`ReadReal`.
- **`ProgramArgs`** — `ArgCount` (excludes the program name),
  `GetArg` (1-based) over `/proc/self/cmdline`.
- **`IOChan`** — opaque `ChanId` over the standard streams;
  `ReadChar`/`WriteChar`/`WriteString`/`WriteLn`/`WriteInt`.
- `runtime/syslib/shim.c` gained the real, string and stdio helpers;
  `SysShim` gained `argc`/`stdin`/`fgetc`/`fwriteint`.
- Docs: `summary_stdlib-conversions.md`,
  `summary_programargs-iochan.md`.

## 3. Language polish

- **Enum literals everywhere**: ordinals assigned at declaration;
  usable in expressions, `=`/`#`/ordering, `CASE` labels, `CONST`
  initialisers and as value/parameter types.
- **String `=`/`#`**: content comparison through the shim.
- **String `+`**: concatenation (strings and a `CHAR` operand); the
  result lives in a static shim buffer — consume it immediately.
- **String assignment** is now a **content copy** (truncated to the
  array capacity, NUL-terminated), replacing the count-checked copy
  that trapped. `a := "abcd"` into capacity 3 yields `"abc"`.
- **`LEN`/`LENGTH`** of string literals fold to the content length.
- Docs: `summary_lang-polish.md`, `summary_strcat.md`.

## 4. Showcase

`compiler/tests/showcase14.mod` (`Showcase14`, exit 42) links seven
modules and exercises the whole session: enums (CASE/CONST/ordering),
string `=`/`#`, `Utf8.Decode`, `Conversions`, `ProgramArgs`, `RealIO`,
`TextIO.U*` and `IOChan`.

```
showcase14 n=42
3.500000E+00 ok ✓
```

Docs: `summary_showcase14.md`.

## Test suite

128 tests (was 111 at the start of the session): run, trap, reject and
session/separate-compilation cases, plus the gm2-import gate. New
this session: `t_unicode`, `t_trap_chr8`, four invalid-UTF-8 rejects,
`utf8_prog`, `utext_prog`, `conv_prog`, `realio_prog`, `t_enum`
(`t_enumdecl` promoted from reject), `t_streq`, `progargs_prog`,
`iochan_prog`, `showcase14`, `t_strcat`, `t_strtrunc`, `t_strempty`.
`expect_run`/`expect_trap` now link the shim.

## Resume

```sh
cd .../m2compiler-V3
./bootstrap/fixpoint.sh                       # FIXPOINT OK
cd compiler && ./build.sh && ./run_tests.sh   # 128/128
```

## Remaining polish

- Strict `231` def/impl signature checks (types, not just arity).
- Variant records (`RECORD CASE`).
- Unicode: `UString` whole-string assignment to a fixed array.
- `IOChan` beyond the standard streams (files, `ReadString`,
  position).
- String concat: a growable/consumer-owned buffer instead of the
  single static 8 KiB slot.