plans: haskell-completeness phases 7-16 + updated loop briefing

String=[Char] via pure-SX views, show, error, numeric tower,
Data.Map, Data.Set, records, IORef, exceptions. Briefing updated
to point at new plan; old phases 1-6 plan untouched.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

plans/agent-briefings/haskell-loop.md

@@ -1,6 +1,8 @@
 # haskell-on-sx loop agent (single agent, queue-driven)
 
-Role: iterates `plans/haskell-on-sx.md` forever. Mini-Haskell 98 with real laziness (SX thunks are first-class). Phases 1-3 are untyped — laziness + ADTs first; HM inference is phase 4.
+Role: iterates `plans/haskell-completeness.md` forever. Mini-Haskell 98 with
+real laziness (SX thunks are first-class). Phases 1–6 are complete; this loop
+works Phases 7–16.
 
 ```
 description: haskell-on-sx queue loop
@@ -11,66 +13,141 @@ isolation: worktree
 
 ## Prompt
 
-You are the sole background agent working `/root/rose-ash/plans/haskell-on-sx.md`. Isolated worktree, forever, one commit per feature. Push to `origin/loops/haskell` after every commit.
-
-**Note:** there's an existing `/root/rose-ash/sx-haskell/` directory (~25 M). Check whether it has prior work you should fold into `lib/haskell/` rather than starting from scratch. Summarise what you find in the first iteration's Progress log entry; do not edit `sx-haskell/` itself.
+You are the sole background agent working
+`/root/rose-ash-loops/haskell/plans/haskell-completeness.md`. Isolated worktree,
+forever, one commit per feature. Push to `origin/loops/haskell` after every commit.
 
 ## Restart baseline — check before iterating
 
-1. Read `plans/haskell-on-sx.md` — roadmap + Progress log.
-2. First-run only: peek at `/root/rose-ash/sx-haskell/` — does any of it belong in `lib/haskell/`? Report in Progress log. Don't edit sx-haskell/.
-3. `ls lib/haskell/` — pick up from the most advanced file.
-4. Run `lib/haskell/tests/*.sx` if they exist. Green before new work.
-5. If `lib/haskell/scoreboard.md` exists, that's your baseline.
+1. Read `plans/haskell-completeness.md` — roadmap + Progress log.
+2. `ls lib/haskell/` — orient on current state.
+3. Run `bash lib/haskell/test.sh`. All 775 tests must be green before new work.
+4. Check `lib/haskell/scoreboard.md` — baseline is 156/156 (18 programs).
 
 ## The queue
 
-Phase order per `plans/haskell-on-sx.md`:
+Phase order per `plans/haskell-completeness.md`:
 
-- **Phase 1** — tokenizer + parser + **layout rule** (indentation-sensitive, painful but required per Haskell 98 §10.3)
-- **Phase 2** — desugar + eager eval + ADTs (`data` declarations, constructor tagging, pattern matching). Still untyped.
-- **Phase 3** — **laziness**: thunk-wrap every application arg, `force` = WHNF, pattern match forces scrutinee. Classic programs (infinite Fibonacci, sieve of Eratosthenes, quicksort, n-queens, expression calculator) green.
-- **Phase 4** — Hindley-Milner type inference (Algorithm W, let-polymorphism, type-sig checking)
-- **Phase 5** — typeclasses (dictionary passing, Eq/Ord/Show/Num/Functor/Monad/Applicative, `deriving`)
-- **Phase 6** — real `IO` monad backed by `perform`/`resume`, full Prelude, drive corpus to 150+
+- **Phase 7** — String = [Char] via O(1) string-view dicts. No OCaml changes.
+  Read the "String-view design" section below before touching anything.
+- **Phase 8** — `show` for arbitrary types; `deriving Show` generates proper
+  instances; `print x = putStrLn (show x)`.
+- **Phase 9** — `error` / `undefined`; partial functions raise; top-level runner
+  catches and a new `hk-test-error` helper checks error messages.
+- **Phase 10** — Numeric tower: `fromIntegral`, Float/Double literals,
+  `sqrt`/`floor`/`ceiling`/`round`/`truncate`, `Fractional`/`Floating` stubs.
+- **Phase 11** — `Data.Map` — weight-balanced BST in pure SX in `map.sx`.
+- **Phase 12** — `Data.Set` — BST in pure SX in `set.sx`.
+- **Phase 13** — `where` in typeclass instances + default methods.
+- **Phase 14** — Record syntax: `data Foo = Foo { bar :: Int }`, accessors,
+  update `r { field = v }`, record patterns.
+- **Phase 15** — `IORef` — mutable cells via existing `perform`/`resume` IO.
+- **Phase 16** — Exception handling: `catch`, `try`, `throwIO`, `evaluate`.
 
 Within a phase, pick the checkbox with the best tests-per-effort ratio.
 
-Every iteration: implement → test → commit → tick `[ ]` → Progress log → next.
+Every iteration: implement → test → commit → tick `[ ]` → Progress log → push.
+
+## String-view design (Phase 7 — read before touching strings)
+
+A string view is a pure-SX dict `{:hk-str buf :hk-off n}`. Native SX strings
+also satisfy `hk-str?` (offset = 0 implicitly). No OCaml changes needed.
+
+- `hk-str?` covers both native strings and view dicts.
+- `hk-str-head v` returns the character at offset `n` as an **integer** (ord
+  value). Char = integer throughout.
+- `hk-str-tail v` returns a new view dict with offset `n+1`; **O(1)**.
+- `hk-str-null? v` is true when offset ≥ string length.
+- In `match.sx`, the `":"` cons-pattern branch checks `hk-str?` on the scrutinee
+  **before** the normal tagged-list path. On a string: head = char-int, tail =
+  shifted view (or `(list "[]")` if exhausted).
+- `chr n` converts an integer back to a single-character SX string for display
+  and for `++`.
+- `++` between two strings concatenates natively via `str`; no cons-spine built.
+- The natural hazard: any code that checks `(list? v)` or `(= (first v) ":")` on
+  a value must be audited — string views are dicts, not lists. Check `hk-str?`
+  first in every dispatch chain.
+
+## Conformance test programs
+
+For each phase's conformance programs:
+
+1. **WebFetch the source** from one of:
+   - 99 Haskell Problems: https://wiki.haskell.org/H-99:_Ninety-Nine_Haskell_Problems
+   - Rosetta Code Haskell: https://rosettacode.org/wiki/Category:Haskell
+   - Self-contained snippets from Real World Haskell / Learn You a Haskell
+2. **Adapt minimally** — no GHC extensions, no external packages beyond
+   `Data.Map`/`Data.Set`/`Data.IORef` (once those phases are done).
+3. **Cite the source** as a comment at the top of the `.sx` test file.
+4. Add the program name (without `.sx`) to `PROGRAMS` in `lib/haskell/conformance.sh`.
+5. Run `bash lib/haskell/conformance.sh` and verify green before committing.
+
+Target: scoreboard grows from 156 → 300+ as phases complete.
 
 ## Ground rules (hard)
 
-- **Scope:** only `lib/haskell/**` and `plans/haskell-on-sx.md`. Do **not** edit `spec/`, `hosts/`, `shared/`, other `lib/<lang>/` dirs, `lib/stdlib.sx`, `lib/` root, or `sx-haskell/`. Haskell primitives go in `lib/haskell/runtime.sx`.
-- **NEVER call `sx_build`.** 600s watchdog. If sx_server binary broken → Blockers entry, stop.
-- **Shared-file issues** → plan's Blockers with minimal repro.
-- **SX thunks** (`make-thunk`, force on use) are already in the trampolining evaluator — reuse. Don't invent your own thunk type.
-- **SX files:** `sx-tree` MCP tools ONLY. `sx_validate` after edits.
-- **Worktree:** commit, then push to `origin/loops/haskell`. Never touch `main`.
+- **Scope:** only `lib/haskell/**` and `plans/haskell-completeness.md`. Do
+  **not** edit `spec/`, `hosts/`, `shared/`, other `lib/<lang>/` dirs,
+  `lib/stdlib.sx`, `lib/` root.
+- **NEVER call `sx_build`.** 600s watchdog. If sx_server binary broken →
+  Blockers entry in the plan, stop.
+- **Shared-file issues** → plan's Blockers section with minimal repro.
+- **SX thunks** (`make-thunk`, force on use) already in the trampolining
+  evaluator — reuse. String views are SX dicts, not thunks.
+- **SX files:** `sx-tree` MCP tools ONLY (`sx_read_subtree`, `sx_find_all`,
+  `sx_replace_node`, `sx_insert_child`, `sx_insert_near`,
+  `sx_replace_by_pattern`, `sx_rename_symbol`, `sx_validate`, `sx_write_file`).
+  `sx_validate` after every edit. Never `Edit`/`Read`/`Write` on `.sx` files.
+- **Shell, Markdown, JSON:** edit with normal tools.
+- **Worktree:** commit then push to `origin/loops/haskell`. Never touch `main`.
 - **Commit granularity:** one feature per commit.
 - **Plan file:** update Progress log + tick boxes every commit.
+- **Tests:** `bash lib/haskell/test.sh` must stay green. Never regress existing
+  775 tests. After new programs, run `bash lib/haskell/conformance.sh`.
 
 ## Haskell-specific gotchas
 
-- **Layout rule is the hard bit of parsing** — you need a lexer-parser feedback loop that inserts virtual `{`, `;`, `}` based on indentation. Budget proportionally.
-- **Every application arg is a thunk** — compiling `f x y` to `(f (thunk x) (thunk y))` not `(f x y)`. Pattern-match forces.
-- **ADT representation:** tagged list, e.g. `data Maybe a = Nothing | Just a` → constructors are `(:Nothing)` (0-ary) and `(:Just <thunk>)` (1-ary). Pattern match on the head symbol.
-- **Let-polymorphism** (phase 4): generalise at let-binding boundaries only, not at lambda.
-- **Typeclass dictionaries** (phase 5): each class is a record type; each instance builds the record; method call = project + apply.
-- **`IO`** (phase 6): internally `World -> (a, World)` but in practice backed by `perform`/`resume` for real side effects. Desugar `do`-notation to `>>=`.
-- **Out of scope:** GHC extensions. No `DataKinds`, `GADTs`, `TypeFamilies`, `TemplateHaskell`. Stick to Haskell 98.
+- **String views are dicts** — `(list? v)` returns false for a string view.
+  Audit every value-dispatch chain in `match.sx` and `eval.sx` for this.
+- **Char = integer** — `'a'` parses to int 97. `chr 97 = "a"` (1-char string).
+  Do not represent Char as a 1-char SX string internally.
+- **`deriving Show`** (Phase 8): nested constructor args need parens if their
+  show string contains a space. Rule: `if string-contains (show arg) " " then
+  "(" ++ show arg ++ ")" else show arg`.
+- **`error` tag** (Phase 9): use `(raise (list "hk-error" msg))`. The top-level
+  `hk-run-io` guard must catch this tag; do not let `hk-error` leak as an
+  uncaught SX exception into the test runner's output.
+- **`Data.Map` module resolution** (Phase 11): qualified imports `import
+  qualified Data.Map as Map` need the eval import handler to resolve the dotted
+  module name to the `map.sx` namespace dict. Check `hk-bind-decls!` import arm.
+- **Record update field index** (Phase 14): `r { field = v }` needs the field →
+  positional-index mapping at runtime. Store it in `hk-constructors` when
+  registering `:con-rec`.
+- **IORef mutation** (Phase 15): `dict-set!` is the SX in-place mutator. The
+  `IORef` dict is heap-allocated and passed by reference — mutation is safe.
+- **Every application arg is a thunk** — `f x y` → `(f (thunk x) (thunk y))`.
+  Pattern-match forces before matching. Builtins force their args.
+- **ADT representation:** `("Just" thunk)`, `("Nothing")`, `(":" h t)`, `("[]")`.
+- **Let-polymorphism:** generalise at let-binding boundaries only, not lambda.
+- **Typeclass dictionaries:** class = record; instance = record value; method
+  call = project + apply. Defaults stored under `"__default__ClassName_method"`,
+  used as fallback when the instance dict lacks the key.
+- **Out of scope:** GHC extensions. No `DataKinds`, `GADTs`, `TypeFamilies`,
+  `TemplateHaskell`. Haskell 98 only.
 
 ## General gotchas (all loops)
 
-- SX `do` = R7RS iteration. Use `begin` for multi-expr sequences.
-- `cond`/`when`/`let` clauses evaluate only the last expr.
+- SX `do` = R7RS iteration. Use `begin` for multi-expression sequences.
+- `cond`/`when`/`let` clauses evaluate only the last expression.
 - `type-of` on user fn returns `"lambda"`.
-- Shell heredoc `||` gets eaten — escape or use `case`.
+- Shell heredoc `||` gets eaten by bash — escape or use `case`.
+- `keys` on an SX dict returns keys in implementation-defined order.
 
 ## Style
 
 - No comments in `.sx` unless non-obvious.
-- No new planning docs — update `plans/haskell-on-sx.md` inline.
-- Short, factual commit messages (`haskell: layout rule + first parse (+10)`).
+- No new planning docs — update `plans/haskell-completeness.md` inline.
+- Short, factual commit messages (`haskell: string-view O(1) head/tail (+15)`).
 - One feature per iteration. Commit. Log. Next.
 
-Go. Read the plan; (first run only) peek at sx-haskell/ and report; find first `[ ]`; implement.
+Go. Read `plans/haskell-completeness.md`; find the first `[ ]`; implement.