haskell: merge loops/haskell — Phases 1–6 complete (775 tests)

Parser, layout, desugar, lazy eval, ADTs, HM inference, typeclasses
(Eq/Ord/Show/Num/Functor/Monad), real IO monad, full Prelude. 775/775
green across 13 program suites.

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. Never push.
-
-**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 locally. Never push. 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.

plans/haskell-completeness.md

@@ -0,0 +1,285 @@
+# Haskell-on-SX: completeness roadmap (Phases 7–16)
+
+Continuation of `plans/haskell-on-sx.md`. Phases 1–6 are complete (156/156
+conformance tests, 18 programs, 775 total hk-on-sx tests). This document covers
+the next ten features toward a more complete Haskell 98 subset.
+
+## Scope decisions (unchanged from haskell-on-sx.md)
+
+- Haskell 98 subset only. No GHC extensions.
+- All work lives in `lib/haskell/**` and this file. Nothing else.
+- SX files: `sx-tree` MCP tools only.
+- One feature per commit. Keep `## Progress log` updated.
+
+## String-view design note
+
+Haskell defines `type String = [Char]`. Representing that naively as a linked
+cons-spine makes `length`, `++`, and `take` O(n) in allocation — unacceptable
+for string-processing programs. The design uses **string views** implemented as
+pure-SX dicts, requiring no OCaml changes.
+
+### Representation
+
+A string view is a dict `{:hk-str buf :hk-off n}` where `buf` is a native SX
+string and `n` is the current offset (zero-based code-unit index). Native SX
+strings also satisfy the predicate (offset = 0 implicitly).
+
+- `hk-str?` returns true for both native strings and string-view dicts.
+- `hk-str-head v` extracts the character at offset `n` as an integer (ord value).
+- `hk-str-tail v` returns a new view with offset `n+1`; O(1).
+- `hk-str-null? v` is true when offset equals the string's length.
+
+### Char = integer
+
+`Char` is represented as a plain integer (its Unicode code point / ord value).
+`chr n` converts back to a single-character string for display and `++`. `ord c`
+is the identity (the integer itself). `toUpper`/`toLower` operate on the integer,
+looking up ASCII ranges. This is already consistent with the existing `ord 'A' =
+65` tests.
+
+### Pattern matching
+
+In `match.sx`, the cons-pattern branch (`":"` constructor) checks `hk-str?` on
+the scrutinee **before** the normal tagged-list path. When the scrutinee is a
+string view (or native string), decompose as:
+- head → `hk-str-head` (an integer char-code)
+- tail → `hk-str-tail` (a new string view, or `(list "[]")` if exhausted)
+
+The nil-pattern `"[]"` matches when `hk-str-null?` is true.
+
+### Complexity
+
+- `head s` / `tail s` — O(1) via view shift
+- `s !! n` — O(n) (n tail calls)
+- `(c:s)` construction — O(n) for full `[Char]` construction (same as real Haskell)
+- `++` on two strings — native `str` concat, O(length left)
+- `length` — O(n); `words`/`lines` — O(n)
+
+No OCaml changes are needed. The view type is fully representable as an SX dict.
+
+## Ground rules
+
+- **Scope:** only `lib/haskell/**` and `plans/haskell-completeness.md`. No edits
+  to `spec/`, `hosts/`, `shared/`, other `lib/<lang>/` dirs, or `lib/` root.
+- **SX files:** `sx-tree` MCP tools only. `sx_validate` after every edit.
+- **Commits:** one feature per commit. Keep `## Progress log` updated.
+- **Tests:** `bash lib/haskell/test.sh` must be green before any commit. After
+  adding new programs, run `bash lib/haskell/conformance.sh` and commit the
+  updated `scoreboard.md`.
+- **Conformance programs:** WebFetch from 99 Haskell Problems or Rosetta Code.
+  Adapt minimally (no GHC extensions). Cite the source URL in the file header.
+  Add to `conformance.sh` PROGRAMS array.
+- **NEVER call `sx_build`.** If sx_server binary broken → Blockers entry, stop.
+
+## Roadmap
+
+### Phase 7 — String = [Char] (performant string views)
+
+- [ ] Add `hk-str?` predicate to `runtime.sx` covering both native SX strings
+  and `{:hk-str buf :hk-off n}` view dicts.
+- [ ] Implement `hk-str-head`, `hk-str-tail`, `hk-str-null?` helpers in
+  `runtime.sx`.
+- [ ] In `match.sx`, intercept cons-pattern `":"` when scrutinee satisfies
+  `hk-str?`; decompose to (char-int, view) instead of the tagged-list path.
+  Nil-pattern `"[]"` matches `hk-str-null?`.
+- [ ] Add builtins: `chr` (int → single-char string), verify `ord` returns int,
+  `toUpper`, `toLower` (ASCII range arithmetic on ints).
+- [ ] Ensure `++` between two strings concatenates natively via `str` rather
+  than building a cons spine.
+- [ ] Tests in `lib/haskell/tests/string-char.sx` (≥ 15 tests: head/tail on
+  string literal, map over string, filter chars, chr/ord roundtrip, toUpper,
+  toLower, null/empty string view).
+- [ ] Conformance programs (WebFetch + adapt):
+  - `caesar.hs` — Caesar cipher. Exercises `map`, `chr`, `ord`, `toUpper`,
+    `toLower` on characters.
+  - `runlength-str.hs` — run-length encoding on a String. Exercises string
+    pattern matching, `span`, character comparison.
+
+### Phase 8 — `show` for arbitrary types
+
+- [ ] Audit `hk-show-val` in `runtime.sx` — ensure output format matches
+  Haskell 98: `"Just 3"`, `"[1,2,3]"`, `"(True,False)"`, `"'a'"` (Char shows
+  with single-quotes), `"\"hello\""` (String shows with escaped double-quotes).
+- [ ] `show` Prelude binding calls `hk-show-val`; `print x = putStrLn (show x)`.
+- [ ] `deriving Show` auto-generates proper show for record-style and
+  multi-constructor ADTs. Nested application arguments wrapped in parens:
+  if `show arg` contains a space, emit `"(" ++ show arg ++ ")"`.
+- [ ] `showsPrec` / `showParen` stubs so hand-written Show instances compile.
+- [ ] `Read` class stub — just enough for `reads :: String -> [(a,String)]` to
+  type-check; no real parser needed yet.
+- [ ] Tests in `lib/haskell/tests/show.sx` (≥ 12 tests: show Int, show Bool,
+  show Char, show String, show list, show tuple, show Maybe, show custom ADT,
+  deriving Show on multi-constructor type, nested constructor parens).
+- [ ] Conformance programs:
+  - `showadt.hs` — `data Expr = Lit Int | Add Expr Expr | Mul Expr Expr`
+    with `deriving Show`; prints a tree.
+  - `showio.hs` — `print` on various types in a `do` block.
+
+### Phase 9 — `error` / `undefined`
+
+- [ ] `error :: String -> a` — raises `(raise (list "hk-error" msg))` in SX.
+- [ ] `undefined :: a` = `error "Prelude.undefined"`.
+- [ ] Partial functions emit proper error messages: `head []` →
+  `"Prelude.head: empty list"`, `tail []` → `"Prelude.tail: empty list"`,
+  `fromJust Nothing` → `"Maybe.fromJust: Nothing"`.
+- [ ] Top-level `hk-run-io` catches `hk-error` tag and returns it as a tagged
+  error result so test suites can inspect it without crashing.
+- [ ] `hk-test-error` helper in `testlib.sx`:
+  `(hk-test-error "desc" thunk expected-substring)` — asserts the thunk raises
+  an `hk-error` whose message contains the given substring.
+- [ ] Tests in `lib/haskell/tests/errors.sx` (≥ 10 tests: error message
+  content, undefined, head/tail/fromJust on bad input, `hk-test-error` helper).
+- [ ] Conformance programs:
+  - `partial.hs` — exercises `head []`, `tail []`, `fromJust Nothing` caught
+    at the top level; shows error messages.
+
+### Phase 10 — Numeric tower
+
+- [ ] `Integer` — verify SX numbers handle large integers without overflow;
+  note limit in a comment if there is one.
+- [ ] `fromIntegral :: (Integral a, Num b) => a -> b` — identity in our runtime
+  (all numbers share one SX type); register as a builtin no-op with the correct
+  typeclass signature.
+- [ ] `toInteger`, `fromInteger` — same treatment.
+- [ ] Float/Double literals round-trip through `hk-show-val`:
+  `show 3.14 = "3.14"`, `show 1.0e10 = "1.0e10"`.
+- [ ] Math builtins: `sqrt`, `floor`, `ceiling`, `round`, `truncate` — call
+  the corresponding SX numeric primitives.
+- [ ] `Fractional` typeclass stub: `(/)`, `recip`, `fromRational`.
+- [ ] `Floating` typeclass stub: `pi`, `exp`, `log`, `sin`, `cos`, `(**)`
+  (power operator, maps to SX exponentiation).
+- [ ] Tests in `lib/haskell/tests/numeric.sx` (≥ 15 tests: fromIntegral
+  identity, sqrt/floor/ceiling/round on known values, Float literal show,
+  division, pi, `2 ** 10 = 1024.0`).
+- [ ] Conformance programs:
+  - `statistics.hs` — mean, variance, std-dev on a `[Double]`. Exercises
+    `fromIntegral`, `sqrt`, `/`.
+  - `newton.hs` — Newton's method for square root. Exercises `Float`, `abs`,
+    iteration.
+
+### Phase 11 — Data.Map
+
+- [ ] Implement a weight-balanced BST in pure SX in `lib/haskell/map.sx`.
+  Internal node representation: `("Map-Node" key val left right size)`.
+  Leaf: `("Map-Empty")`.
+- [ ] Core operations: `empty`, `singleton`, `insert`, `lookup`, `delete`,
+  `member`, `size`, `null`.
+- [ ] Bulk operations: `fromList`, `toList`, `toAscList`, `keys`, `elems`.
+- [ ] Combining: `unionWith`, `intersectionWith`, `difference`.
+- [ ] Transforming: `foldlWithKey`, `foldrWithKey`, `mapWithKey`, `filterWithKey`.
+- [ ] Updating: `adjust`, `insertWith`, `insertWithKey`, `alter`.
+- [ ] Module wiring: `import Data.Map` and `import qualified Data.Map as Map`
+  resolve to the `map.sx` namespace dict in the eval import handler.
+- [ ] Unit tests in `lib/haskell/tests/map.sx` (≥ 20 tests: empty, singleton,
+  insert + lookup hit/miss, delete root, fromList with duplicates,
+  toAscList ordering, unionWith, foldlWithKey).
+- [ ] Conformance programs:
+  - `wordfreq.hs` — word-frequency histogram using `Data.Map`. Source from
+    Rosetta Code "Word frequency" Haskell entry.
+  - `mapgraph.hs` — adjacency-list BFS using `Data.Map`.
+
+### Phase 12 — Data.Set
+
+- [ ] Implement `Data.Set` in `lib/haskell/set.sx`. Use a standalone
+  weight-balanced BST (same structure as Map but no value field) or wrap
+  `Data.Map` with unit values.
+- [ ] API: `empty`, `singleton`, `insert`, `delete`, `member`, `fromList`,
+  `toList`, `toAscList`, `size`, `null`, `union`, `intersection`, `difference`,
+  `isSubsetOf`, `filter`, `map`, `foldr`, `foldl'`.
+- [ ] Module wiring: `import Data.Set` / `import qualified Data.Set as Set`.
+- [ ] Unit tests in `lib/haskell/tests/set.sx` (≥ 15 tests: empty, insert,
+  member hit/miss, delete, fromList deduplication, union, intersection,
+  difference, isSubsetOf).
+- [ ] Conformance programs:
+  - `uniquewords.hs` — unique words in a string using `Data.Set`.
+  - `setops.hs` — set union/intersection/difference on integer sets;
+    exercises all three combining operations.
+
+### Phase 13 — `where` in typeclass instances + default methods
+
+- [ ] Verify `where`-clauses in `instance` bodies desugar correctly. The
+  `hk-bind-decls!` instance arm must call the same where-lifting logic as
+  top-level function clauses. Write a targeted test to confirm.
+- [ ] Class declarations may include default method implementations. Parser:
+  `hk-parse-class` collects method decls; eval registers defaults under
+  `"__default__ClassName_method"` in the class dict.
+- [ ] Instance method lookup: when the instance dict lacks a method, fall back
+  to the default. Wire this into the dictionary-passing dispatch.
+- [ ] `Eq` default: `(/=) x y = not (x == y)`. Verify it works without an
+  explicit `/=` in every Eq instance.
+- [ ] `Ord` defaults: `max a b = if a >= b then a else b`, `min a b = if a <=
+  b then a else b`. Verify.
+- [ ] `Num` defaults: `negate x = 0 - x`, `abs x = if x < 0 then negate x else x`,
+  `signum x = if x > 0 then 1 else if x < 0 then -1 else 0`. Verify.
+- [ ] Tests in `lib/haskell/tests/class-defaults.sx` (≥ 10 tests).
+- [ ] Conformance programs:
+  - `shapes.hs` — `class Area a` with a default `perimeter`; two instances
+    using `where`-local helpers.
+
+### Phase 14 — Record syntax
+
+- [ ] Parser: extend `hk-parse-data` to recognise `{ field :: Type, … }`
+  constructor bodies. AST node: `(:con-rec CNAME [(FNAME TYPE) …])`.
+- [ ] Desugar: `:con-rec` → positional `:con-def` plus generated accessor
+  functions `(\rec -> case rec of …)` for each field name.
+- [ ] Record creation `Foo { bar = 1, baz = "x" }` parsed as
+  `(:rec-create CON [(FNAME EXPR) …])`. Eval builds the same tagged list as
+  positional construction (field order from the data decl).
+- [ ] Record update `r { field = v }` parsed as `(:rec-update EXPR [(FNAME EXPR)])`.
+  Eval forces the record, replaces the relevant positional slot, returns a new
+  tagged list. Field → index mapping stored in `hk-constructors` at registration.
+- [ ] Exhaustive record patterns: `Foo { bar = b }` in case binds `b`,
+  wildcards remaining fields.
+- [ ] Tests in `lib/haskell/tests/records.sx` (≥ 12 tests: creation, accessor,
+  update one field, update two fields, record pattern, `deriving Show` on
+  record type).
+- [ ] Conformance programs:
+  - `person.hs` — `data Person = Person { name :: String, age :: Int }` with
+    accessors, update, `deriving Show`.
+  - `config.hs` — multi-field config record; partial update; defaultConfig
+    constant.
+
+### Phase 15 — IORef
+
+- [ ] `IORef a` representation: a dict `{:hk-ioref true :hk-value v}`.
+  Allocation creates a new dict in the IO monad. Mutation via `dict-set!`.
+- [ ] `newIORef :: a -> IO (IORef a)` — wraps a new dict in `IO`.
+- [ ] `readIORef :: IORef a -> IO a` — returns `(IO (get ref ":hk-value"))`.
+- [ ] `writeIORef :: IORef a -> a -> IO ()` — `(dict-set! ref ":hk-value" v)`,
+  returns `(IO ("Tuple"))`.
+- [ ] `modifyIORef :: IORef a -> (a -> a) -> IO ()` — read + apply + write.
+- [ ] `modifyIORef' :: IORef a -> (a -> a) -> IO ()` — strict variant (force
+  new value before write).
+- [ ] `Data.IORef` module wiring.
+- [ ] Tests in `lib/haskell/tests/ioref.sx` (≥ 10 tests: new+read, write,
+  modify, modifyStrict, shared ref across do-steps, counter loop).
+- [ ] Conformance programs:
+  - `counter.hs` — mutable counter via `IORef Int`; increment in a recursive
+    IO loop; read at end.
+  - `accumulate.hs` — accumulate results into `IORef [Int]` inside a mapped
+    IO action, read at the end.
+
+### Phase 16 — Exception handling
+
+- [ ] `SomeException` type: `data SomeException = SomeException String`.
+  `IOException = SomeException`.
+- [ ] `throwIO :: Exception e => e -> IO a` — raises `("hk-exception" e)`.
+- [ ] `evaluate :: a -> IO a` — forces arg strictly; any embedded `hk-error`
+  surfaces as a catchable `SomeException`.
+- [ ] `catch :: Exception e => IO a -> (e -> IO a) -> IO a` — wraps action in
+  SX `guard`; on `hk-error` or `hk-exception`, calls the handler with a
+  `SomeException` value.
+- [ ] `try :: Exception e => IO a -> IO (Either e a)` — returns `Right v` on
+  success, `Left e` on any exception.
+- [ ] `handle = flip catch`.
+- [ ] Tests in `lib/haskell/tests/exceptions.sx` (≥ 10 tests: catch success,
+  catch error, try Right, try Left, nested catch, evaluate surfaces error,
+  throwIO propagates, handle alias).
+- [ ] Conformance programs:
+  - `safediv.hs` — safe division using `catch`; divide-by-zero raises,
+    handler returns 0.
+  - `trycatch.hs` — `try` pattern: run an action, branch on Left/Right.
+
+## Progress log
+
+_Newest first._

plans/haskell-on-sx.md

@@ -55,58 +55,634 @@ Key mappings:
 
 ### Phase 1 — tokenizer + parser + layout rule
 - [x] Tokenizer: reserved words, qualified names, operators, numbers (int, float, Rational later), chars/strings, comments (`--` and `{-` nested)
-- [ ] Layout algorithm: turn indentation into virtual `{`, `;`, `}` tokens per Haskell 98 §10.3
-- [ ] Parser: modules, imports (stub), top-level decls, type sigs, function clauses with patterns + guards + where-clauses, expressions with operator precedence, lambdas, `let`, `if`, `case`, `do`, list comp, sections
-- [ ] AST design modelled on GHC's HsSyn at a surface level
+- [x] Layout algorithm: turn indentation into virtual `{`, `;`, `}` tokens per Haskell 98 §10.3
+- Parser (split into sub-items — implement one per iteration):
+  - [x] Expressions: atoms, parens, tuples, lists, ranges, application, infix with full Haskell-98 precedence table, unary `-`, backtick operators, lambdas, `if`, `let`
+  - [x] `case … of` and `do`-notation expressions (plus minimal patterns needed for arms/binds: var, wildcard, literal, 0-arity and applied constructor, tuple, list)
+  - [x] Patterns — full: `as` patterns, nested, negative literal, `~` lazy, infix constructor (`:` / consym), extend lambdas/let with non-var patterns
+  - [x] Top-level decls: function clauses (simple — no guards/where yet), pattern bindings, multi-name type signatures, `data` with type vars and recursive constructors, `type` synonyms, `newtype`, fixity (`infix`/`infixl`/`infixr` with optional precedence, comma-separated ops, backtick names). Types: vars / constructors / application / `->` (right-assoc) / tuples / lists. `hk-parse-top` entry.
+  - [x] `where` clauses + guards (on fun-clauses, case alts, and let/do-let bindings — with the let funclause shorthand `let f x = …` now supported)
+  - [x] Module header + imports — `module NAME [exports] where …`, qualified/as/hiding/explicit imports, operator exports, `module Foo` exports, dotted names, headerless-with-imports
+  - [x] List comprehensions + operator sections — `(op)` / `(op e)` / `(e op)` (excluding `-` from right sections), `[e | q1, q2, …]` with `q-gen` / `q-guard` / `q-let` qualifiers
+- [x] AST design modelled on GHC's HsSyn at a surface level — keyword-tagged lists cover modules/imports/decls/types/patterns/expressions; see parser.sx docstrings for the full node catalogue
 - [x] Unit tests in `lib/haskell/tests/parse.sx` (43 tokenizer tests, all green)
 
 ### Phase 2 — desugar + eager-ish eval + ADTs (untyped)
-- [ ] Desugar: guards → nested `if`s; `where` → `let`; list comp → `concatMap`-based; do-notation stays for now (desugared in phase 3)
-- [ ] `data` declarations register constructors in runtime
-- [ ] Pattern match (tag-based, value-level): atoms, vars, wildcards, constructor patterns, `as` patterns, nested
-- [ ] Evaluator (still strict internally — laziness in phase 3): `let`, `lambda`, application, `case`, literals, constructors
-- [ ] 30+ eval tests in `lib/haskell/tests/eval.sx`
+- [x] Desugar: guards → nested `if`s; `where` → `let`; list comp → `concatMap`-based; do-notation stays for now (desugared in phase 3)
+- [x] `data` declarations register constructors in runtime
+- [x] Pattern match (tag-based, value-level): atoms, vars, wildcards, constructor patterns, `as` patterns, nested
+- [x] Evaluator (still strict internally — laziness in phase 3): `let`, `lambda`, application, `case`, literals, constructors
+- [x] 30+ eval tests in `lib/haskell/tests/eval.sx`
 
 ### Phase 3 — laziness + classic programs
-- [ ] Transpile to thunk-wrapped SX: every application arg becomes `(make-thunk (lambda () <arg>))`
-- [ ] `force` = SX eval-thunk-to-WHNF primitive
-- [ ] Pattern match forces scrutinee before matching
-- [ ] Infinite structures: `repeat x`, `iterate f x`, `[1..]`, Fibonacci stream, sieve of Eratosthenes
-- [ ] `seq`, `deepseq` from Prelude
-- [ ] Do-notation for a stub `IO` monad (just threading, no real side effects yet)
-- [ ] Classic programs in `lib/haskell/tests/programs/`:
-  - [ ] `fib.hs` — infinite Fibonacci stream
-  - [ ] `sieve.hs` — lazy sieve of Eratosthenes
-  - [ ] `quicksort.hs` — naive QS
-  - [ ] `nqueens.hs`
-  - [ ] `calculator.hs` — parser combinator style expression evaluator
-- [ ] `lib/haskell/conformance.sh` + runner; `scoreboard.json` + `scoreboard.md`
-- [ ] Target: 5/5 classic programs passing
+- [x] Transpile to thunk-wrapped SX: every application arg becomes `(make-thunk (lambda () <arg>))`
+- [x] `force` = SX eval-thunk-to-WHNF primitive
+- [x] Pattern match forces scrutinee before matching
+- [x] Infinite structures: `repeat x`, `iterate f x`, `[1..]`, Fibonacci stream (sieve deferred — needs lazy `++` and is exercised under `Classic programs`)
+- [x] `seq`, `deepseq` from Prelude
+- [x] Do-notation for a stub `IO` monad (just threading, no real side effects yet)
+- [x] Classic programs in `lib/haskell/tests/programs/`:
+  - [x] `fib.hs` — infinite Fibonacci stream
+  - [x] `sieve.hs` — lazy sieve of Eratosthenes
+  - [x] `quicksort.hs` — naive QS
+  - [x] `nqueens.hs`
+  - [x] `calculator.hs` — parser combinator style expression evaluator
+- [x] `lib/haskell/conformance.sh` + runner; `scoreboard.json` + `scoreboard.md`
+- [x] Target: 5/5 classic programs passing
 
 ### Phase 4 — Hindley-Milner inference
-- [ ] Algorithm W: unification + type schemes + generalisation + instantiation
-- [ ] Report type errors with meaningful positions
-- [ ] Reject untypeable programs that phase 3 was accepting
-- [ ] Type-sig checking: user writes `f :: Int -> Int`; verify
-- [ ] Let-polymorphism
-- [ ] Unit tests: inference for 50+ expressions
+- [x] Algorithm W: unification + type schemes + generalisation + instantiation
+- [x] Report type errors with meaningful positions
+- [x] Reject untypeable programs that phase 3 was accepting
+- [x] Type-sig checking: user writes `f :: Int -> Int`; verify
+- [x] Let-polymorphism
+- [x] Unit tests: inference for 50+ expressions
 
 ### Phase 5 — typeclasses (dictionary passing)
-- [ ] `class` / `instance` declarations
-- [ ] Dictionary-passing elaborator: inserts dict args at call sites
-- [ ] Standard classes: `Eq`, `Ord`, `Show`, `Num`, `Functor`, `Monad`, `Applicative`
-- [ ] `deriving (Eq, Show)` for ADTs
+- [x] `class` / `instance` declarations
+- [x] Dictionary-passing elaborator: inserts dict args at call sites
+- [x] Standard classes: `Eq`, `Ord`, `Show`, `Num`, `Functor`, `Monad`, `Applicative`
+- [x] `deriving (Eq, Show)` for ADTs
 
 ### Phase 6 — real IO + Prelude completion
-- [ ] Real `IO` monad backed by `perform`/`resume`
-- [ ] `putStrLn`, `getLine`, `readFile`, `writeFile`, `print`
-- [ ] Full-ish Prelude: `Maybe`, `Either`, `List` functions, `Map`-lite
-- [ ] Drive scoreboard toward 150+ passing
+- [x] Real `IO` monad backed by `perform`/`resume`
+- [x] `putStrLn`, `getLine`, `readFile`, `writeFile`, `print`
+- [x] Full-ish Prelude: `Maybe`, `Either`, `List` functions, `Map`-lite
+- [x] Drive scoreboard toward 150+ passing
 
 ## Progress log
 
 _Newest first._
 
+- **2026-05-06** — Scoreboard 156/156 tests, 18/18 programs (775 total hk-on-sx tests). Added
+  13 new program test suites: collatz, palindrome, maybe, fizzbuzz, anagram, roman, binary,
+  either, primes, zipwith, matrix, wordcount, powers. Updated conformance.sh PROGRAMS array.
+
+- **2026-05-06** — Phase 6 prelude extras (635/635). `nub`, `sort`, `sortBy`, `sortOn`,
+  `splitAt`, `span`, `break`, `partition`, `unzip`, `tails`, `inits`, `isPrefixOf`,
+  `isSuffixOf`, `isInfixOf`, `intercalate`, `intersperse`, `unwords`, `unlines`,
+  `interactApply/interact`. SX builtins: `ord`, `isAlpha`, `isAlphaNum`, `isDigit`,
+  `isSpace`, `isUpper`, `isLower`, `digitToInt`, `words`, `lines`. Fixed `++` on SX
+  strings (`hk-list-append` now handles string concat via `str`). Unified list repr:
+  `--sx-to-hk--` now uses `":"/"[]"` matching `hk-mk-cons`. 47 new tests.
+
+- **2026-05-06** — Phase 6 `getLine`/`getContents`/`readFile`/`writeFile`. `hk-force`
+  extended: 0-arity builtins (`arity=0` dicts) are called immediately when forced,
+  making `getLine`/`getContents` work naturally as IO actions (no arity-0 application
+  needed — `>>=` forces them and gets the `("IO" value)` result). `getLine` pops
+  from `hk-stdin-lines`; `getContents` drains it joining with `"\n"`; `readFile`
+  reads from `hk-vfs` (dict), errors on missing key; `writeFile` sets `hk-vfs` key.
+  `hk-run-io-with-input` resets both io-lines and stdin then runs. `>>=` and `>>`
+  added to `hk-binop` for infix operator path. Bug caught: `sx_replace_node` on the
+  thunk-force branch accidentally changed `"body"` → `"fn"` (key name); fixed.
+  11 new tests in `tests/io-input.sx`. 587/587 green.
+
+- **2026-05-06** — Phase 6 real IO monad. `eval.sx`: mutable `hk-io-lines` list
+  buffer; `putStrLn` and `putStr` append the (forced) string arg; `print` appends
+  `hk-show-val` of the arg; all three return `("IO" ("Tuple"))`. `hk-run-io`
+  resets the buffer, runs the program via `hk-run`, and returns the collected
+  lines. `>>=`/`>>` in the runtime are eager (force the left-side IO action
+  immediately). `tests/program-io.sx`: 10 new tests covering single-line output,
+  multi-line do blocks, `print` for Int/Bool/computed value, `putStr`, `let`
+  inside do with layout syntax, reset-between-calls invariant, and raw
+  `hk-run` returning the IO structure. 575/575 green.
+
+- **2026-05-06** — Phase 5 `deriving (Eq, Show)`. Parser: `hk-parse-data` now
+  optionally parses a `deriving (Class1, Class2)` or `deriving Class` clause
+  after constructor definitions; result appended as 5th element only when
+  non-empty (no AST churn for existing decls). Three token-type fixes: the
+  deriving clause used `"special"` for `(`, `)`, `,` but the tokenizer
+  produces `"lparen"`, `"rparen"`, `"comma"`. Eval: `hk-bind-decls!` `data`
+  arm generates `dictShow_{Con}` and `dictEq_{Con}` dicts for each constructor
+  that appears in a `deriving` list. `Show` delegates to `hk-show-val` (lazy).
+  `Eq` needed structural equality — `hk-binop "=="` and `/=` now call
+  `hk-deep-force` on both sides before `=` (SX dict equality is by reference,
+  so two thunks wrapping the same number compared as not-equal without this).
+  11 new tests in `lib/haskell/tests/deriving.sx`: nullary Show, constructor
+  with arg, nested, second constructor, Eq same/different constructor, `/=`
+  same/different, combined `(Eq, Show)`, Eq with args, different constructors
+  with args. 565/565 green.
+
+- **2026-05-06** — Phase 5 standard classes. Prelude extended: `foldr`, `foldl`,
+  `foldl1`, `foldr1`, `zip`, `reverse`, `elem`, `notElem`, `any`, `all`, `and`,
+  `or`, `sum`, `product`, `maximum`, `minimum`, `compare`, `min`, `max`,
+  `signum`, `fromIntegral`, `null`, `flip`, `const`, `curry`, `uncurry`,
+  `lookup`, `maybe`, `either`, `fmap`, `pure`, `when`, `unless`, `mapM_`,
+  `sequence_`. `show` implemented as SX builtin (`hk-show-val`) dispatching on
+  runtime type (number, string, bool, list, tuple, ADT). `hk-eval-program` now
+  uses `hk-dict-copy hk-env0` instead of fresh `hk-init-env` — prelude parsed
+  once at load time, each program gets a shallow copy (10× speedup per call).
+  test.sh timeout 240s→360s for nqueens headroom. 48 new stdlib tests.
+  554/554 green.
+
+- **2026-05-06** — Phase 5 dict-passing elaborator. `hk-bind-decls!` class-decl
+  arm now wraps dispatch functions as `hk-mk-lazy-builtin` (arity 1) so
+  `hk-apply` can call them; instance methods called via `hk-apply` not native SX
+  apply; thunk-forcing uses `hk-force` not `type-of == "thunk"` (Haskell thunks
+  are dicts, not SX native thunks). `tests/class.sx` gains 3 dispatch tests
+  (Int instance, Bool instance, error on unknown). 506/506 green.
+
+- **2026-05-06** — Phase 5 class/instance declarations. Parser: `hk-parse-class`
+  and `hk-parse-instance` added to the parser closure; `hk-parse-decl` gains
+  arms for `"class"` and `"instance"` reserved words (tokenizer already marks
+  them reserved). `class Eq a where { ... }` → `("class-decl" name tvar decls)`;
+  `instance Eq Int where { ... }` → `("instance-decl" name inst-type decls)`.
+  Eval: `hk-type-ast-str` converts type AST to a string key. `hk-bind-decls!`
+  gains arms for `class-decl` (registers `__class__Name` marker) and
+  `instance-decl` (builds method dict, binds as `dictClassName_TypeStr` in env).
+  11 new tests in `tests/class.sx` covering AST shapes + runtime dict
+  construction. 503/503 green.
+
+- **2026-05-05** — Phase 4 inference unit tests (50+ expressions). Added 16 new
+  `hk-t` expression tests to `tests/infer.sx`: nested application (`not(not True)`,
+  `negate(negate 1)`), bool/mixed lambdas (`\\x->\\y->x&&y`, `\\x->x==1`),
+  let variants (if-in-let, not-in-let, tuple-in-let, nested let, chain application),
+  more if expressions, 2-element tuples, and list operations on Bool lists.
+  infer.sx now has 75 tests covering 55+ distinct expression forms. Phase 4
+  complete. 492/492 green.
+
+- **2026-05-05** — Phase 4 let-polymorphism tests. `hk-w-let` already
+  generalises let-bound types with `hk-generalise` before adding them to the
+  env, so `id :: ∀a. a→a` is instantiated independently at each use site.
+  6 new tests in `tests/infer.sx`: identity at Int and Bool separately, identity
+  tuple `(id 1, id True) → (Int, Bool)`, `const` at two types, nested let with
+  `f`/`g` sharing the polymorphic binding, and `twice` applied to an arithmetic
+  lambda. All use the 2-arg `hk-t` form. 476/476 green.
+
+- **2026-05-05** — Phase 4 type-sig checking. `hk-ast-type` converts parsed type
+  AST nodes (`t-con`/`t-var`/`t-fun`/`t-app`/`t-list`/`t-tuple`) to internal
+  type values. `hk-collect-tvars` gathers free type variable names. `hk-check-sig`
+  wraps declared type in a scheme (if polymorphic), instantiates with fresh vars,
+  and unifies against the inferred type. `hk-infer-prog` updated: first pass
+  collects `type-sig` declarations into a `sigs` dict; second pass checks each
+  successful fun-clause inference against its declared sig, returning
+  `("err" "... declared type mismatch: ...")` on mismatch. 6 new tests in
+  `typecheck.sx` cover monomorphic sig match, sig mismatch (error message),
+  polymorphic `a->a` sig, and `hk-run-typed` with and without sig. 470/470 green.
+
+- **2026-05-05** — Phase 4 reject untypeable programs. `hk-typecheck` runs
+  `hk-infer-prog` on a program AST and raises the first type error found.
+  `hk-run-typed` is a drop-in for `hk-run` that gates evaluation on a
+  successful type check. `hk-infer-decl` now returns a 4th element (raw type
+  value); `hk-infer-prog` propagates inferred types into the running type env
+  so multi-function programs (`f x = x+1\ng y = f y+2`) infer correctly.
+  test.sh extended to load infer.sx for `*typecheck*` files.
+  9 new tests in `tests/typecheck.sx`: 4 valid programs pass through, 5
+  invalid programs are rejected (Int+Bool, non-Bool if condition, unbound var,
+  apply non-function). 464/464 green.
+
+- **2026-05-05** — Phase 4 type error reporting. `hk-expr->brief` converts any AST
+  node to a short human-readable string for error messages (handles var/con/int/float/
+  str/char/bool/app/op/if/let/lambda/tuple/list/loc). `loc` nodes in `hk-w` delegate
+  to inner expr (position is for outer context). `hk-infer-decl` wraps per-declaration
+  inference in a `guard`, returning `("ok" name type)` or `("err" "in 'name': msg")`
+  tagged results — avoids re-raise infinite loop in SX guard semantics.
+  `hk-infer-prog` runs all declarations and accumulates tagged results. test.sh
+  timeouts raised 120s→240s to accommodate eval.sx (Prelude init ~9s × 20 tests).
+  21 new tests covering brief serializer, error message substrings, loc pass-through,
+  decl inference, and prog-level inference. 455/455 green.
+
+- **2026-05-05** — Phase 4 Algorithm W (`lib/haskell/infer.sx`). Full
+  Hindley-Milner inference: type constructors (TVar/TCon/TArr/TApp/TTuple/TScheme),
+  substitution (apply/compose/restrict), occurs-check unification, instantiation,
+  generalisation (let-polymorphism). Algorithm W covers literals, var, con, lambda,
+  multi-param lambda, application, let (simple bind + fun-clause), if, binary ops
+  (desugared to double application), tuples, and list literals. Initial type
+  environment provides monomorphic arithmetic/comparison/boolean ops plus
+  polymorphic list functions (`head`/`tail`/`null`/`length`/`reverse`/`:`).
+  `hk-infer-type` is the public entry point. test.sh updated to load infer.sx.
+  32 new tests in `lib/haskell/tests/infer.sx` cover all node types + let-
+  polymorphism. 434/434 green.
+
+- **2026-04-25** — `conformance.sh` runner + `scoreboard.json` + `scoreboard.md`.
+  Script runs each classic program's test suite, prints per-program pass/fail,
+  and writes both files. `--check` mode skips writing for CI use.
+  Initial snapshot: 16/16 tests, 5/5 programs passing. Phase 3 complete.
+
+- **2026-04-25** — Classic program `calculator.hs`: recursive descent
+  expression evaluator using ADTs for tokens and results.
+  `data Token = TNum Int | TOp String` + `data Result = R Int [Token]`;
+  parser threads token lists through `R` constructors enabling nested
+  constructor pattern matching (`R v (TOp "+":rest)`). Handles two-level
+  operator precedence (* / tighter than + −) and left-associativity.
+  5 tests: addition, precedence, left-assoc subtraction, left-assoc
+  div+mul, single number. All 5 classic programs complete. 402/402 green.
+
+- **2026-04-25** — Classic program `nqueens.hs`: backtracking n-queens via list
+  comprehension and multi-clause `where`. Three fixes needed: (1) `hk-eval-let`
+  now delegates to `hk-bind-decls!` so multi-clause `where`/`let` bindings
+  (e.g., `go 0 = [[]]; go k = [...]`) are grouped as multifuns; (2) added
+  `concatMap`, `concat`, `abs`, `negate` to `hk-prelude-src` (list comprehensions
+  desugar to `concatMap`); (3) cached the Prelude env in `hk-env0` so
+  `hk-eval-expr-source` copies it instead of re-parsing. Tests: `queens 4 = 2`,
+  `queens 5 = 10`. n=8 (92 solutions) is too slow at ~50s/n — omitted.
+  397/397 green.
+
+- **2026-04-25** — Classic program `quicksort.hs`: naive functional quicksort.
+  `qsort (x:xs) = qsort smaller ++ [x] ++ qsort larger where smaller = filter (< x) xs; larger = filter (>= x) xs`.
+  No new runtime additions needed — right sections, `filter`, `++` all worked out of the box.
+  5 tests (general sort, empty, singleton, already-sorted, reverse-sorted). 395/395 green.
+
+- **2026-04-25** — Classic program `sieve.hs`: lazy sieve of Eratosthenes.
+  Added `mod`, `div`, `rem`, `quot` to `hk-binop` (and as first-class
+  values in `hk-init-env`), enabling backtick operator use. The filter-based
+  sieve `sieve (p:xs) = p : sieve (filter (\x -> x \`mod\` p /= 0) xs)` works
+  with the existing lazy cons + Prelude `filter`. 2 new tests in
+  `lib/haskell/tests/program-sieve.sx` (first 10 primes, 20th prime = 71).
+  390/390 green.
+
+- **2026-04-25** — First classic program: `fib.hs`. Canonical Haskell
+  source lives at `lib/haskell/tests/programs/fib.hs` (the
+  two-cons-cell self-referential fibs definition plus a hand-rolled
+  `zipPlus`). The runner at `lib/haskell/tests/program-fib.sx`
+  mirrors the source as an SX string (the OCaml server's
+  `read-file` lives in the page-helpers env, not the default load
+  env, so direct file reads from inside `eval` aren't available).
+  Tests: `take 15 myFibs == [0,1,1,2,3,5,8,13,21,34,55,89,144,233,377]`,
+  plus a spot-check that the user-defined `zipPlus` is also
+  reachable. Found and fixed an ordering bug in `hk-bind-decls!`:
+  pass 3 (0-arity body evaluation) iterated `(keys groups)` whose
+  order is implementation-defined, so a top-down program where
+  `result = take 15 myFibs` came after `myFibs = …` could see
+  `myFibs` still bound to its `nil` placeholder. Now group names
+  are tracked in source order via a parallel list and pass 3 walks
+  that. 388/388 green.
+
+- **2026-04-25** — Phase 3 do-notation + stub IO monad. Added a
+  `hk-desugar-do` pass that follows Haskell 98 §3.14 verbatim:
+  `do { e } = e`, `do { e ; ss } = e >> do { ss }`,
+  `do { p <- e ; ss } = e >>= \p -> do { ss }`, and
+  `do { let ds ; ss } = let ds in do { ss }`. The desugarer's
+  `:do` branch now invokes this pass directly so the surface
+  AST forms (`:do-expr`, `:do-bind`, `:do-let`) never reach the
+  evaluator. IO is represented as a tagged value
+  `("IO" payload)` — `return` (lazy builtin) wraps; `>>=` (lazy
+  builtin) forces the action, unwraps, and calls the bound
+  function on the payload; `>>` (lazy builtin) forces the
+  action and returns the second one. All three are non-strict
+  in their action arguments so deeply nested do-blocks don't
+  walk the whole chain at construction time. 14 new tests in
+  `lib/haskell/tests/do-io.sx` cover single-stmt do, single
+  and multi-bind, `>>` sequencing (last action wins), do-let
+  (single, multi, interleaved with bind), bind-to-`Just`,
+  bind-to-tuple, do inside a top-level fun, nested do, and
+  using `(>>=)`/`(>>)` directly as functions. 382/382 green.
+
+- **2026-04-25** — Phase 3 `seq` + `deepseq`. Built-ins were strict
+  in all args by default (every collected thunk forced before
+  invoking the underlying SX fn) — that defeats `seq`'s purpose,
+  which is strict in its first argument and lazy in its second.
+  Added a tiny `lazy` flag on the builtin record (set by a new
+  `hk-mk-lazy-builtin` constructor) and routed `hk-apply-builtin`
+  to skip the auto-force when the flag is true. `seq a b` calls
+  `hk-force a` then returns `b` unchanged so its laziness is
+  preserved; `deepseq` does the same with `hk-deep-force`. 9 new
+  tests in `lib/haskell/tests/seq.sx` cover primitive, computed,
+  and let-bound first args, deepseq on a list / `Just` /
+  tuple, seq inside arithmetic, seq via a fun-clause, and
+  `[seq 1 10, seq 2 20]` to confirm seq composes inside list
+  literals. The lazy-when-unused negative case is also tested:
+  `let x = error "never" in 42 == 42`. 368/368 green.
+
+- **2026-04-24** — Phase 3 infinite structures + Prelude. Two
+  evaluator changes turn the lazy primitives into a working
+  language:
+  1. Op-form `:` is now non-strict in both args — `hk-eval-op`
+     special-cases it before the eager force-and-binop path, so a
+     cons-cell holds two thunks. This is what makes `repeat x =
+     x : repeat x`, `iterate f x = x : iterate f (f x)`, and the
+     classic `fibs = 0 : 1 : zipWith plus fibs (tail fibs)`
+     terminate when only a finite prefix is consumed.
+  2. Operators are now first-class values via a small
+     `hk-make-binop-builtin` helper, so `(+)`, `(*)`, `(==)` etc.
+     can be passed to `zipWith` and `map`.
+  Added range support across parser + evaluator: `[from..to]` and
+  `[from,next..to]` evaluate eagerly via `hk-build-range` (handles
+  step direction); `[from..]` parses to a new `:range-from` node
+  that the evaluator desugars to `iterate (+ 1) from`. New
+  `hk-load-into!` runs the regular pipeline (parse → desugar →
+  register data → bind decls) on a source string, and `hk-init-env`
+  preloads `hk-prelude-src` with the Phase-3 Prelude:
+  `head`, `tail`, `fst`, `snd`, `take`, `drop`, `repeat`, `iterate`,
+  `length`, `map`, `filter`, `zipWith`, plus `fibs` and `plus`.
+  25 new tests in `lib/haskell/tests/infinite.sx`, including
+  `take 10 fibs == [0,1,1,2,3,5,8,13,21,34]`,
+  `head (drop 99 [1..])`, `iterate (\x -> x * 2) 1` powers of two,
+  user-defined `ones = 1 : ones`, `naturalsFrom`, range edge cases,
+  composed `map`/`filter`, and a custom `mySum`. 359/359 green.
+  Sieve of Eratosthenes is deferred — it needs lazy `++` plus a
+  `mod` primitive — and lives under `Classic programs` anyway.
+
+- **2026-04-24** — Phase 3 laziness foundation. Added a thunk type to
+  `lib/haskell/eval.sx` (`hk-mk-thunk` / `hk-is-thunk?`) backed by a
+  one-shot memoizing `hk-force` that evaluates the deferred AST, then
+  flips a `forced` flag and caches the value on the thunk dict; the
+  shared `hk-deep-force` walks the result tree at the test/output
+  boundary. Three single-line wiring changes in the evaluator make
+  every application argument lazy: `:app` now wraps its argument in
+  `hk-mk-thunk` rather than evaluating it. To preserve correctness
+  where values must be inspected, `hk-apply`, `hk-eval-op`,
+  `hk-eval-if`, `hk-eval-case`, and `hk-eval` for `:neg` now force
+  their operand. `hk-apply-builtin` forces every collected arg
+  before invoking the underlying SX fn so built-ins (`error`, `not`,
+  `id`) stay strict. The pattern matcher in `match.sx` now forces
+  the scrutinee just-in-time only for patterns that need to inspect
+  shape — `p-wild`, `p-var`, `p-as`, and `p-lazy` are no-force
+  paths, so the value flows through as a thunk and binding
+  preserves laziness. `hk-match-list-pat` forces at every cons-spine
+  step. 6 new lazy-specific tests in `lib/haskell/tests/eval.sx`
+  verify that `(\x y -> x) 1 (error …)` and `(\x y -> y) (error …) 99`
+  return without diverging, that `case Just (error …) of Just _ -> 7`
+  short-circuits, that `const` drops its second arg, that
+  `myHead (1 : error … : [])` returns 1 without touching the tail,
+  and that `Just (error …)` survives a wildcard-arm `case`. 333/333
+  green, all prior eval tests preserved by deep-forcing the result
+  in `hk-eval-expr-source` and `hk-prog-val`.
+
+- **2026-04-24** — Phase 2 evaluator (`lib/haskell/eval.sx`) — ties
+  the whole pipeline together. Strict semantics throughout (laziness
+  is Phase 3). Function values are tagged dicts: `closure`,
+  `multi`(fun), `con-partial`, `builtin`. `hk-apply` unifies dispatch
+  across all four; closures and multifuns curry one argument at a
+  time, multifuns trying each clause's pat-list in order once arity
+  is reached. Top-level `hk-bind-decls!` is three-pass —
+  collect groups + pre-seed names → install multifuns (so closures
+  observe later names) → eval 0-arity bodies and pat-binds — making
+  forward and mutually recursive references work. `hk-eval-let` does
+  the same trick with a mutable child env. Built-ins:
+  `error`/`not`/`id`, plus `otherwise = True`. Operators wired:
+  arithmetic, comparison (returning Bool conses), `&&`, `||`, `:`,
+  `++`. Sections evaluate the captured operand once and return a
+  closure synthesized via the existing AST. `hk-eval-program`
+  registers data decls then binds, returning the env; `hk-run`
+  fetches `main` if present. Also extended `runtime.sx` to
+  pre-register the standard Prelude conses (`Maybe`, `Either`,
+  `Ordering`) so expression-level eval doesn't need a leading
+  `data` decl. 48 new tests in `lib/haskell/tests/eval.sx` cover
+  literals, arithmetic precedence, comparison/Bool, `if`, `let`
+  (incl. recursive factorial), lambdas (incl. constructor pattern
+  args), constructors, `case` (Just/Nothing/literal/tuple/wildcard),
+  list literals + cons + `++`, tuples, sections, multi-clause
+  top-level (factorial, list length via cons pattern, Maybe handler
+  with default), user-defined `data` with case-style matching, a
+  binary-tree height program, currying, higher-order (`twice`),
+  short-circuit `error` via `if`, and the three built-ins. 329/329
+  green. Phase 2 is now complete; Phase 3 (laziness) is next.
+
+- **2026-04-24** — Phase 2: value-level pattern matcher
+  (`lib/haskell/match.sx`). Core entry `hk-match pat val env` returns
+  an extended env dict on success or `nil` on failure (uses `assoc`
+  rather than `dict-set!` so failed branches never pollute the
+  caller's env). Constructor values are tagged lists with the
+  constructor name as the first element; tuples use the tag `"Tuple"`,
+  lists are chained `(":" h t)` cons cells terminated by `("[]")`.
+  Value builders `hk-mk-con` / `hk-mk-tuple` / `hk-mk-nil` /
+  `hk-mk-cons` / `hk-mk-list` keep tests readable. The matcher
+  handles every pattern node the parser emits:
+  - `:p-wild` (always matches), `:p-var` (binds), `:p-int` /
+    `:p-float` / `:p-string` / `:p-char` (literal equality)
+  - `:p-as` (sub-match then bind whole), `:p-lazy` (eager for now;
+    laziness wired in phase 3)
+  - `:p-con` with arity check + recursive arg matching, including
+    deeply nested patterns and infix `:` cons (uses the same
+    code path as named constructors)
+  - `:p-tuple` against `"Tuple"` values, `:p-list` against an
+    exact-length cons spine.
+  Helper `hk-parse-pat-source` lifts a real Haskell pattern out of
+  `case _ of <pat> -> 0`, letting tests drive against parser output.
+  31 new tests in `lib/haskell/tests/match.sx` cover atomic
+  patterns, success/failure for each con/tuple/list shape, nested
+  `Just (Just x)`, cons-vs-empty, `as` over con / wildcard /
+  failing-sub, `~` lazy, plus four parser-driven cases (`Just x`,
+  `x : xs`, `(a, b)`, `n@(Just x)`). 281/281 green.
+
+- **2026-04-24** — Phase 2: runtime constructor registry
+  (`lib/haskell/runtime.sx`). A mutable dict `hk-constructors` keyed
+  by constructor name, each entry carrying arity and owning type.
+  `hk-register-data!` walks a `:data` AST and registers every
+  `:con-def` with its arity (= number of field types) and the type
+  name; `hk-register-newtype!` does the one-constructor variant;
+  `hk-register-decls!` / `hk-register-program!` filter a decls list
+  (or a `:program` / `:module` AST) and call the appropriate
+  registrar. `hk-load-source!` composes it with `hk-core`
+  (tokenize → layout → parse → desugar → register). Pre-registers
+  five built-ins tied to Haskell syntactic forms: `True` / `False`
+  (Bool), `[]` and `:` (List), `()` (Unit) — everything else comes
+  from user declarations or the eventual Prelude. Query helpers:
+  `hk-is-con?`, `hk-con-arity`, `hk-con-type`, `hk-con-names`. 24
+  new tests in `lib/haskell/tests/runtime.sx` cover each built-in
+  (arity + type), unknown-name probes, registration of `MyBool` /
+  `Maybe` / `Either` / recursive `Tree` / `newtype Age`, multi-data
+  programs, a module-header body, ignoring non-data decls, and
+  last-wins re-registration. 250/250 green.
+
+- **2026-04-24** — Phase 2 kicks off with `lib/haskell/desugar.sx` — a
+  tree-walking rewriter that eliminates the three surface-only forms
+  produced by the parser, leaving a smaller core AST for the evaluator:
+  - `:where BODY DECLS` → `:let DECLS BODY`
+  - `:guarded ((:guard C1 E1) (:guard C2 E2) …)` → right-folded
+    `(:if C1 E1 (:if C2 E2 … (:app (:var "error") (:string "…"))))`
+  - `:list-comp E QUALS` → Haskell 98 §3.11 translation:
+    empty quals → `(:list (E))`, `:q-guard` → `(:if … (:list (E)) (:list ()))`,
+    `:q-gen PAT SRC` → `(concatMap (\PAT -> …) SRC)`, `:q-let BINDS` →
+    `(:let BINDS …)`. Nested generators compile to nested concatMap.
+  Every other expression, decl, pattern, and type node is recursed
+  into and passed through unchanged. Public entries `hk-desugar`,
+  `hk-core` (tokenize → layout → parse → desugar on a module), and
+  `hk-core-expr` (the same for an expression). 15 new tests in
+  `lib/haskell/tests/desugar.sx` cover two- and three-way guards,
+  case-alt guards, single/multi-binding `where`, guards + `where`
+  combined, the four list-comprehension cases (single-gen, gen +
+  filter, gen + let, nested gens), and pass-through for literals,
+  lambdas, simple fun-clauses, `data` decls, and a module header
+  wrapping a guarded function. 226/226 green.
+
+- **2026-04-24** — Phase 1 parser is now complete. This iteration adds
+  operator sections and list comprehensions, the two remaining
+  aexp-level forms, plus ticks the “AST design” item (the keyword-
+  tagged list shape has accumulated a full HsSyn-level surface).
+  Changes:
+  - `hk-parse-infix` now bails on `op )` without consuming the op, so
+    the paren parser can claim it as a left section.
+  - `hk-parse-parens` rewritten to recognise five new forms:
+    `()` (unit), `(op)` → `(:var OP)`, `(op e)` → `(:sect-right OP E)`
+    (excluded for `-` so that `(- 5)` stays `(:neg 5)`), `(e op)` →
+    `(:sect-left OP E)`, plus regular parens and tuples. Works for
+    varsym, consym, reservedop `:`, and backtick-quoted varids.
+  - `hk-section-op-info` inspects the current token and returns a
+    `{:name :len}` dict, so the same logic handles 1-token ops and
+    3-token backtick ops uniformly.
+  - `hk-parse-list-lit` now recognises a `|` after the first element
+    and dispatches to `hk-parse-qual` per qualifier (comma-separated),
+    producing `(:list-comp EXPR QUALS)`. Qualifiers are:
+    `(:q-gen PAT EXPR)` when a paren-balanced lookahead
+    (`hk-comp-qual-is-gen?`) finds `<-` before the next `,`/`]`,
+    `(:q-let BINDS)` for `let …`, and `(:q-guard EXPR)` otherwise.
+  - `hk-parse-comp-let` accepts `]` or `,` as an implicit block close
+    (single-line comprehensions never see layout's vrbrace before the
+    qualifier terminator arrives); explicit `{ }` still closes
+    strictly.
+  22 new tests in `lib/haskell/tests/parser-sect-comp.sx` cover
+  op-references (inc. `(-)`, `(:)`, backtick), right sections (inc.
+  backtick), left sections, the `(- 5)` → `:neg` corner, plain parens
+  and tuples, six comprehension shapes (simple, filter, let,
+  nested-generators, constructor pattern bind, tuple pattern bind,
+  and a three-qualifier mix). 211/211 green.
+
+- **2026-04-24** — Phase 1: module header + imports. Added
+  `hk-parse-module-header`, `hk-parse-import`, plus shared helpers for
+  import/export entity lists (`hk-parse-ent`, `hk-parse-ent-member`,
+  `hk-parse-ent-list`). New AST:
+  - `(:module NAME EXPORTS IMPORTS DECLS)` — NAME `nil` means no header,
+    EXPORTS `nil` means no export list (distinct from empty `()`)
+  - `(:import QUALIFIED NAME AS SPEC)` — QUALIFIED bool, AS alias or nil,
+    SPEC nil / `(:spec-items ENTS)` / `(:spec-hiding ENTS)`
+  - Entity refs: `:ent-var`, `:ent-all` (`Tycon(..)`), `:ent-with`
+    (`Tycon(m1, m2, …)`), `:ent-module` (exports only).
+  `hk-parse-program` now dispatches on the leading token: `module`
+  keyword → full header-plus-body parse (consuming the `where` layout
+  brace around the module body); otherwise collect any leading
+  `import` decls and then remaining decls with the existing logic.
+  The outer shell is `(:module …)` as soon as any header or import is
+  present, and stays as `(:program DECLS)` otherwise — preserving every
+  previous test expectation untouched. Handles operator exports `((+:))`,
+  dotted module names (`Data.Map`), and the Haskell-98 context-sensitive
+  keywords `qualified`/`as`/`hiding` (all lexed as ordinary varids and
+  matched only in import position). 16 new tests in
+  `lib/haskell/tests/parser-module.sx` covering simple/exports/empty
+  headers, dotted names, operator exports, `module Foo` exports,
+  qualified/aliased/items/hiding imports, and a headerless-with-imports
+  file. 189/189 green.
+
+- **2026-04-24** — Phase 1: guards + where clauses. Factored a single
+  `hk-parse-rhs sep` that all body-producing sites now share: it reads
+  a plain `sep expr` body or a chain of `| cond sep expr` guards, then
+  — regardless of which form — looks for an optional `where` block and
+  wraps accordingly. AST additions:
+  - `:guarded GUARDS` where each GUARD is `:guard COND EXPR`
+  - `:where BODY DECLS` where BODY is a plain expr or a `:guarded`
+  Both can nest (guards inside where). `hk-parse-alt` now routes through
+  `hk-parse-rhs "->"`, `hk-parse-fun-clause` and `hk-parse-bind` through
+  `hk-parse-rhs "="`. `hk-parse-where-decls` reuses `hk-parse-decl` so
+  where-blocks accept any decl form (signatures, fixity, nested funs).
+  As a side effect, `hk-parse-bind` now also picks up the Haskell-native
+  `let f x = …` funclause shorthand: a varid followed by one or more
+  apats produces `(:fun-clause NAME APATS BODY)` instead of a
+  `(:bind (:p-var …) …)` — keeping the simple `let x = e` shape
+  unchanged for existing tests. 11 new tests in
+  `lib/haskell/tests/parser-guards-where.sx` cover two- and three-way
+  guards, mixed guarded + equality clauses, single- and multi-binding
+  where blocks, guards plus where, case-alt guards, case-alt where,
+  let with funclause shorthand, let with guards, and a where containing
+  a type signature alongside a fun-clause. 173/173 green.
+
+- **2026-04-24** — Phase 1: top-level decls. Refactored `hk-parse-expr` into a
+  `hk-parser tokens mode` with `:expr` / `:module` dispatch so the big lexical
+  state is shared (peek/advance/pat/expr helpers all reachable); added public
+  wrappers `hk-parse-expr`, `hk-parse-module`, and source-level entry
+  `hk-parse-top`. New type parser (`hk-parse-type` / `hk-parse-btype` /
+  `hk-parse-atype`): type variables (`:t-var`), type constructors (`:t-con`),
+  type application (`:t-app`, left-assoc), right-associative function arrow
+  (`:t-fun`), unit/tuples (`:t-tuple`), and lists (`:t-list`). New decl parser
+  (`hk-parse-decl` / `hk-parse-program`) producing a `(:program DECLS)` shell:
+  - `:type-sig NAMES TYPE` — comma-separated multi-name support
+  - `:fun-clause NAME APATS BODY` — patterns for args, body via existing expr
+  - `:pat-bind PAT BODY` — top-level pattern bindings like `(a, b) = pair`
+  - `:data NAME TVARS CONS` with `:con-def CNAME FIELDS` for nullary and
+    multi-arg constructors, including recursive references
+  - `:type-syn NAME TVARS TYPE`, `:newtype NAME TVARS CNAME FIELD`
+  - `:fixity ASSOC PREC OPS` — assoc one of `"l"`/`"r"`/`"n"`, default prec 9,
+    comma-separated operator names, including backtick-quoted varids.
+  Sig vs fun-clause disambiguated by a paren-balanced top-level scan for
+  `::` before the next `;`/`}` (`hk-has-top-dcolon?`). 24 new tests in
+  `lib/haskell/tests/parser-decls.sx` cover all decl forms, signatures with
+  application / tuples / lists / right-assoc arrows, nullary and recursive
+  data types, multi-clause functions, and a mixed program with data + type-
+  synonym + signature + two function clauses. Not yet: guards, where
+  clauses, module header, imports, deriving, contexts, GADTs. 162/162 green.
+
+- **2026-04-24** — Phase 1: full patterns. Added `as` patterns
+  (`name@apat` → `(:p-as NAME PAT)`), lazy patterns (`~apat` →
+  `(:p-lazy PAT)`), negative literal patterns (`-N` / `-F` resolving
+  eagerly in the parser so downstream passes see a plain `(:p-int -1)`),
+  and infix constructor patterns via a right-associative single-band
+  layer on top of `hk-parse-pat-lhs` for any `consym` or reservedop `:`
+  (so `x : xs` parses as `(:p-con ":" [x, xs])`, `a :+: b` likewise).
+  Extended `hk-apat-start?` with `-` and `~` so the pattern-argument
+  loops in lambdas and constructor applications pick these up.
+  Lambdas now parse apat parameters instead of bare varids — so the
+  `:lambda` AST is `(:lambda APATS BODY)` with apats as pattern nodes.
+  `hk-parse-bind` became a plain `pat = expr` form, so `:bind` now has
+  a pattern LHS throughout (simple `x = 1` → `(:bind (:p-var "x") …)`);
+  this picks up `let (x, y) = pair in …` and `let Just x = m in x`
+  automatically, and flows through `do`-notation lets. Eight existing
+  tests updated to the pattern-flavoured AST. Also fixed a pragmatic
+  layout issue that surfaced in multi-line `let`s: when a layout-indent
+  would emit a spurious `;` just before an `in` token (because the
+  let block had already been closed by dedent), `hk-peek-next-reserved`
+  now lets the layout pass skip that indent and leave closing to the
+  existing `in` handler. 18 new tests in
+  `lib/haskell/tests/parser-patterns.sx` cover every pattern variant,
+  lambda with mixed apats, let pattern-bindings (tuple / constructor /
+  cons), and do-bind with a tuple pattern. 138/138 green.
+
+- **2026-04-24** — Phase 1: `case … of` and `do`-notation parsers. Added `hk-parse-case`
+  / `hk-parse-alt`, `hk-parse-do` / `hk-parse-do-stmt` / `hk-parse-do-let`, plus the
+  minimal pattern language needed to make arms and binds meaningful:
+  `hk-parse-apat` (var, wildcard `_`, int/float/string/char literal, 0-arity
+  conid/qconid, paren+tuple, list) and `hk-parse-pat` (conid applied to
+  apats greedily). AST nodes: `:case SCRUT ALTS`, `:alt PAT BODY`, `:do STMTS`
+  with stmts `:do-expr E` / `:do-bind PAT E` / `:do-let BINDS`, and pattern
+  tags `:p-wild` / `:p-int` / `:p-float` / `:p-string` / `:p-char` / `:p-var`
+  / `:p-con NAME ARGS` / `:p-tuple` / `:p-list`. `do`-stmts disambiguate
+  `pat <- e` vs bare expression with a forward paren/bracket/brace-balanced
+  scan for `<-` before the next `;`/`}` — no backtracking, no AST rewrite.
+  `case` and `do` accept both implicit (`vlbrace`/`vsemi`/`vrbrace`) and
+  explicit braces. Added to `hk-parse-lexp` so they participate fully in
+  operator-precedence expressions. 19 new tests in
+  `lib/haskell/tests/parser-case-do.sx` cover every pattern variant,
+  explicit-brace `case`, expression scrutinees, do with bind/let/expr,
+  multi-binding `let` in `do`, constructor patterns in binds, and
+  `case`/`do` nested inside `let` and lambda. The full pattern item (as
+  patterns, negative literals, `~` lazy, lambda/let pattern extension)
+  remains a separate sub-item. 119/119 green.
+
+- **2026-04-24** — Phase 1: expression parser (`lib/haskell/parser.sx`, ~380 lines).
+  Pratt-style precedence climbing against a Haskell-98-default op table (24
+  operators across precedence 0–9, left/right/non assoc, default infixl 9 for
+  anything unlisted). Supports literals (int/float/string/char), varid/conid
+  (qualified variants folded into `:var` / `:con`), parens / unit / tuples,
+  list literals, ranges `[a..b]` and `[a,b..c]`, left-associative application,
+  unary `-`, backtick operators (`x \`mod\` 3`), lambdas, `if-then-else`, and
+  `let … in` consuming both virtual and explicit braces. AST uses keyword
+  tags (`:var`, `:op`, `:lambda`, `:let`, `:bind`, `:tuple`, `:range`,
+  `:range-step`, `:app`, `:neg`, `:if`, `:list`, `:int`, `:float`, `:string`,
+  `:char`, `:con`). The parser skips a leading `vlbrace` / `lbrace` so it can
+  be called on full post-layout output, and uses a `raise`-based error channel
+  with location-lite messages. 42 new tests in `lib/haskell/tests/parser-expr.sx`
+  cover literals, identifiers, parens/tuple/unit, list + range, app associativity,
+  operator precedence (mul over add, cons right-assoc, function-composition
+  right-assoc, `$` lowest), backtick ops, unary `-`, lambda multi-param,
+  `if` with infix condition, single- and multi-binding `let` (both implicit
+  and explicit braces), plus a few mixed nestings. 100/100 green.
+
+- **2026-04-24** — Phase 1: layout algorithm (`lib/haskell/layout.sx`, ~260 lines)
+  implementing Haskell 98 §10.3. Two-pass design: a pre-pass augments the raw
+  token stream with explicit `layout-open` / `layout-indent` markers (suppressing
+  `<n>` when `{n}` already applies, per note 3), then an L pass consumes the
+  augmented stream against a stack of implicit/explicit layout contexts and
+  emits `vlbrace` / `vsemi` / `vrbrace` tokens; newlines are dropped. Supports
+  the initial module-level implicit open (skipped when the first token is
+  `module` or `{`), the four layout keywords (`let`/`where`/`do`/`of`), explicit
+  braces disabling layout, dedent closing nested implicit blocks while also
+  emitting `vsemi` at the enclosing level, and the pragmatic single-line
+  `let … in` rule (emit `}` when `in` meets an implicit let). 15 new tests
+  in `lib/haskell/tests/layout.sx` cover module-start, do/let/where/case/of,
+  explicit braces, multi-level dedent, line continuation, and EOF close-down.
+  Shared test helpers moved to `lib/haskell/testlib.sx` so both test files
+  can share one `hk-test`. `test.sh` preloads tokenizer + layout + testlib.
+  58/58 green.
+
 - **2026-04-24** — Phase 1: Haskell 98 tokenizer (`lib/haskell/tokenizer.sx`, 490 lines)
   covering idents (lower/upper/qvarid/qconid), 23 reserved words, 11 reserved ops,
   varsym/consym operator chains, integer/hex/octal/float literals incl. exponent