haskell: case/do + minimal patterns (+19 tests, 119/119)

plans/haskell-on-sx.md

@@ -58,8 +58,8 @@ Key mappings:
 - [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`
-  - [ ] `case … of` and `do`-notation expressions
-  - [ ] Patterns (var, wildcard, literal, constructor, as, nested) — consumed by lambdas, let, case, and function clauses
+  - [x] `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, extend lambdas/let with non-var patterns
   - [ ] Top-level decls: function clauses, type signatures, `data`, `type`, `newtype`, fixity decls
   - [ ] `where` clauses + guards
   - [ ] Module header + imports (stub)
@@ -114,6 +114,27 @@ Key mappings:
 
 _Newest first._
 
+- **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