rose-ash/plans/haskell-on-sx.md

Haskell-on-SX: mini-Haskell with real laziness

Mini-Haskell is the research-paper-worthy demo. Laziness is native to the SX runtime (thunks are already a first-class type); algebraic data types map onto tagged lists; typeclasses map onto dictionary passing; IO maps onto perform/resume. Hindley-Milner inference is the one real piece of new work.

End-state goal: a Haskell 98 subset that runs the small classic programs (sieve of Eratosthenes lazy stream, fibonacci as infinite list, naive quicksort, n-queens, expression evaluator) plus a ~150-test corpus.

Scope decisions (defaults — override)

• Standard: Haskell 98 subset. No GHC extensions (no DataKinds, no GADTs, no TypeFamilies, no TemplateHaskell).
• Phase 1-3 are untyped — we get the evaluator right first with laziness + ADTs, then add HM inference in phase 4. This is deliberate: typing is the hard bit and will take a full phase on its own.
• Typeclasses: dictionary passing, no overlap, no orphan instances. Added in phase 5.
• Layout rule: yes — phase 1 implements Haskell's indentation-sensitive parsing (painful but required).
• Test corpus: custom. No GHC test suite. Bundle classic programs + ~100 hand-written expression-level tests + mini Prelude tests.

Ground rules

• Scope: only lib/haskell/** and plans/haskell-on-sx.md. No edits to spec/, hosts/, shared/, or other language dirs.
• SX files: sx-tree MCP tools only.
• Architecture: Haskell source → AST → desugared-core → SX AST → CEK. Thunks on the SX side provide laziness natively.
• Commits: one feature per commit. Keep ## Progress log updated.

Architecture sketch

Haskell source
    │
    ▼
lib/haskell/tokenizer.sx  — idents, operators, layout-sensitive indentation
    │
    ▼
lib/haskell/parser.sx     — AST: modules, data decls, type sigs, fn clauses, expressions
    │
    ▼
lib/haskell/desugar.sx    — surface → core: case-of-case, do-notation, list comp, guards
    │
    ▼
lib/haskell/transpile.sx  — core → SX AST, wrapping everything in thunks for laziness
    │
    ▼
lib/haskell/runtime.sx    — force, ADT constructors, Prelude, typeclass dicts (phase 5+)
    │
    ▼
existing CEK / VM

Key mappings:

• Laziness = every function argument is an SX thunk; force is WHNF reduction. SX already has make-thunk from the trampolining evaluator — we reuse it.
• Pattern match = forces the scrutinee to WHNF, then structural match on the tag
• ADT = data Maybe a = Nothing | Just a compiles to tagged lists: (:Nothing) and (:Just <thunk>)
• Typeclass = each class becomes a record type; each instance becomes a record value; each method becomes a projection; the elaborator inserts the dict at each call site (phase 5)
• IO = IO a is a function World -> (a, World) internally; in practice uses perform/resume for actual side effects
• Layout = offside rule; inserted virtual braces + semis during a lexer-parser feedback pass

Roadmap

Phase 1 — tokenizer + parser + layout rule

• 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 (split into sub-items — implement one per iteration):
  • Expressions: atoms, parens, tuples, lists, ranges, application, infix with full Haskell-98 precedence table, unary -, backtick operators, lambdas, if, let
  • case … of and do-notation expressions (plus minimal patterns needed for arms/binds: var, wildcard, literal, 0-arity and applied constructor, tuple, list)
  • Patterns — full: as patterns, nested, negative literal, ~ lazy, infix constructor (: / consym), extend lambdas/let with non-var patterns
  • 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.
  • where clauses + guards (on fun-clauses, case alts, and let/do-let bindings — with the let funclause shorthand let f x = … now supported)
  • Module header + imports — module NAME [exports] where …, qualified/as/hiding/explicit imports, operator exports, module Foo exports, dotted names, headerless-with-imports
  • List comprehensions + operator sections — (op) / (op e) / (e op) (excluding - from right sections), [e | q1, q2, …] with q-gen / q-guard / q-let qualifiers
• 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
• Unit tests in lib/haskell/tests/parse.sx (43 tokenizer tests, all green)

Phase 2 — desugar + eager-ish eval + ADTs (untyped)

• Desugar: guards → nested ifs; 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

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 deferred — needs lazy ++ and is exercised under Classic programs)
• 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

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

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

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

Progress log

Newest first.

• 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 lets: 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/lbraceso it can be called on full post-layout output, and uses araise-based error channel with location-lite messages. 42 new tests in lib/haskell/tests/parser-expr.sxcover 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, ifwith infix condition, single- and multi-bindinglet` (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 notation, char + string literals with escape sequences, nested {- ... -} block comments with depth counter, -- ... EOL line comments (respecting the "followed by symbol = not a comment" Haskell 98 rule), backticks, punctuation, and explicit newline tokens for the upcoming layout pass. 43 structural tests in lib/haskell/tests/parse.sx, a lightweight hk-deep=? equality helper and a custom lib/haskell/test.sh runner (pipes through the OCaml epoch protocol, falls back to the main-repo build when run from a worktree). 43/43 green.

  Also peeked at /root/rose-ash/sx-haskell/ per briefing: that directory is a Haskell program implementing an SX interpreter (Types.hs, Eval.hs, Primitives.hs, etc. — ~2800 lines of .hs) — the opposite direction from this project. Nothing to fold in.

  Gotchas hit: emit! and peek are SX evaluator special forms, so every local helper uses the hk- prefix. cond/when/let clauses evaluate ONLY the last expression; multi-expression bodies MUST be wrapped in (do ...). These two together account for all the tokenizer's early crashes.

Blockers

• (none yet)