# Session summary — DList showcase and generics limitation fixes (2026-10-16)

Branch **`resolve-check`**, tree clean.  Suite **219/219**; fixpoint
**OK (3,714,376 bytes)**; corpus **372 OK / 0 crash**.

Tags this arc: `v3-showcase23`, `v3-generics-limitations-fixed`.

## The showcase

`showcase23` is a **generic doubly linked list**: `DList (T : TYPE)`
with `Node`/`List` records, `Init`/`Append`/`Prepend`/`Count`/`Get`/
`Sum`/`Reverse`/`ForEach`, instantiated as `IntList = DList(INTEGER)`.
It exercises a type parameter, **arithmetic over it** (`Sum`), and a
**procedure parameter** (`ForEach` with an imported visitor):

```
list: 5 10 20
sum=35          (Sum over T)
foreach=35      (ForEach + imported visitor procedure)
reversed: 20 10 5
```

Files: `showcase23lib.def/.mod` (generic), `showcase23int.def/.mod`
(refinement), `showcase23vis.def/.mod` (the visitor), `showcase23.mod`
(the program).  Wired as `expect_run_files_out Showcase23 35 "list: 5 10 20"`.

## Bug fixed — global record data size (general)

`QbeGen.RecItems` emitted `w 0` (4 bytes) for *every* scalar record
field, including pointers/`LONGINT`/proc (8 bytes), so a global of such
a record was **under-sized** and later globals clobbered its tail
(`List.count` read as 0).  Now emits `l 0` for
`ClPtr`/`ClLong`/`ClProc`.  Regression `t_recptr`.

## Limitations fixed (`65f331e`)

1. **Arithmetic/relations over a type formal** — the expression checks
   (`ArithCheck`/`RelCheck`/`BoolCheck`/`OrdCheck`/`InCheck`/`EqCheck`)
   now skip on `Resolve(x) = InvalidType` (as `Assignable` already did),
   so an unbound formal is *unknown* in the template and checked
   normally once bound.  (`Sum` over `T` works.)
2. **Proc-typed formals in a DEF/IMPL pair** — `FormalOk` compares two
   `FProc` formals structurally (`ProcTypesOk`), like open arrays,
   instead of by `TypeIndex`.  No more false `235`.
3. **Imported procedure used as a value** — `LowerProcAddr` falls back
   to `SymTab.SymBase(nm)`, so `f := Visitor.Add` resolves to the code
   address (was `0`).  (`t_importproc`.)

## Verify

```sh
cd .../m2compiler-V3/compiler
./M2 ../stdlib/sysio.def ../stdlib/sysio.mod \
    tests/showcase23lib.def tests/showcase23lib.mod \
    tests/showcase23int.def tests/showcase23int.mod \
    tests/showcase23vis.def tests/showcase23vis.mod tests/showcase23.mod
# -> list: 5 10 20 / sum=35 / foreach=35 / reversed: 20 10 5, exit 35
```

## Standing generics status

Type/value/procedure parameters, constraints
(`ORDINAL`/`INTEGER`/`REAL`/`POINTER`/`SCALAR`), nested generics, and
generic classes (via generic modules) all work; see
`docs/summary_generics-closed-2026-10-16.md`.