# Session summary — Unicode (UCHAR/UString) + stdlib Conversions/RealIO

Date 2026-09-28 (second save). Suite **122/122**; self-hosting
fixpoint **OK** (`bootstrap/fixpoint.sh`, image **2,062,392 bytes**).
`master`, tree clean except the user's uncommitted `compiler/toto.mod`.

Tags this session: `v3-unicode-1`, `v3-unicode-2`,
`v3-stdlib-conversions`, `v3-unicode-stdlib-summary` (this doc).

## 1. Unicode step — complete

Implemented in two increments (`docs/summary_unicode.md`).

**Increment 1 — types, literals, conversions** (`af09dc6`, `v3-unicode-1`)

- `UCHAR`: 32-bit codepoint `0..1114111` (QBE `w`), a distinct type
  (`ClUChar`/`FUChar`), usable in declarations and `ARRAY OF UCHAR`.
- `U'..'` / `U".."` literals (`ustring` token). One codepoint → `UCHAR`
  immediate; otherwise a **UString** descriptor
  `data $ustrN = { l count, w cp0, … }` — which is a V3
  length-prefixed array, so a literal is a valid actual for an open
  `ARRAY OF UCHAR` formal.
- Strict RFC 3629 decoding (`QbeGen.DeclUStr`): overlong, surrogate
  (`D800..DFFF`), `>10FFFF`, truncation → semantic error
  **234 `invalid UTF-8 in U-literal`**.
- `UCHR`, `CHR8` (l-domain `0..255` check → trap), `UORD`.

**Increment 2 — codec + output** (`f1bfd76`, `v3-unicode-2`)

- `runtime/syslib/Utf8` — `Decode`/`Encode` (`MaxUTF8Length = 4`,
  `MaxCodePoint = 1114111`).
- `TextIO.UWriteChar` / `UWriteString(VAR u: ARRAY OF UCHAR)` /
  `UWriteLn` — real UTF-8 on stdout (verified byte-for-byte).

**Flagged deviations from the locked design**

- `UORD` returns `INTEGER`, not `LONGCARD`: V3 has no `LONGCARD` type
  name and no 64→32-bit conversion, so a `LONGCARD` result would be
  unusable in codegen; a codepoint fits in 32 bits.
- `UCHR` also accepts an integer-family operand (the `UCHAR`
  constructor), so a computed codepoint can be built without a literal.
- The *front end* decodes in `QbeGen.DeclUStr`: Stage 1 is gm2-built
  and does not know `UCHAR`, so the compiler cannot import `Utf8`.
- `.ssa` is still written when error 234 fires (image gate pending).

## 2. stdlib — Conversions + RealIO

(`2f80422`, `v3-stdlib-conversions`; `docs/summary_stdlib-conversions.md`.)

- `Conversions`: `IntToStr`/`CardToStr` (M2), `RealToStr` (shim
  `%.6E`), `StrToInt`/`StrToCard` (whole-string parse), `StrToReal`
  (shim `strtod`) — `BOOLEAN` results.
- `RealIO`: `WriteReal`, `WriteRealF(x, width)`, `ReadReal`.
- `runtime/syslib/shim.c`: `m2realstr`, `m2strreal`,
  `m2writereal(f)`, `m2readreal`.

`Conversions` uses `BOOLEAN` rather than the ISO `ConvResults`
enumeration (V3 enumeration values in expressions are still `230`).

## Tests added this session

- `t_unicode.mod` (exit 31) — `U'é'`, `U'😀'`, `U'€'`, `UCHR`, `CHR8`,
  `UORD`.
- `t_trap_chr8.mod` — `CHR8(U'😀')` aborts (rc 134).
- `t_bad_overlong.mod`, `t_bad_surrogate.mod`, `t_bad_utf8big.mod`,
  `t_bad_truncutf.mod` — expect error 234 (raw invalid bytes; `.LST`
  output git-ignored).
- `utf8_prog.mod` (exit 127) — `Utf8` round-trips.
- `utext_prog.mod` — `TextIO.UWriteString(U"héllo")` → stdout `héllo`.
- `conv_prog.mod` (exit 127) — `Conversions` round-trips.
- `realio_prog.mod` (exit 42) — `WriteReal`→`3.500000E+00`, reads
  `1.25`.

## Tags of interest

- `v3-unicode-1` — `af09dc6` (types/literals/conversions).
- `v3-unicode-2` — `f1bfd76` (codec + UTF-8 output).
- `v3-stdlib-conversions` — `2f80422` (`Conversions`/`RealIO`).
- Earlier milestones: `v3-fixpoint`, `v3-bootstrap`,
  `v3-stdlib-broaden`, `v3-selfhosting`.

## Resume

```sh
cd .../m2compiler-V3
./bootstrap/fixpoint.sh                       # FIXPOINT OK
cd compiler && ./build.sh && ./run_tests.sh   # 122/122
```

## Remaining polish

- Unicode: `UString` whole-string assignment to a *fixed* array
  (the count check traps, as it does for `CHAR` arrays today);
  UString `=`/`+`/concat.
- stdlib: `ProgramArgs` (shim `m2argc`/`m2arg` already exist),
  `IOChan`; `ConvResults` once enumerations are usable in
  expressions.
- Language: enum literals in expressions / `CASE` labels; strict
  `231` def/impl signature checks; suppressing `.ssa` on error 234.