haskell: full patterns — as/lazy/negative/infix + lambda & let pat LHS (+18 tests, 138/138)

plans/haskell-on-sx.md

@@ -59,7 +59,7 @@ Key mappings:
 - 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)
-  - [ ] Patterns — full: `as` patterns, nested, negative literal, `~` lazy, extend lambdas/let with non-var patterns
+  - [x] Patterns — full: `as` patterns, nested, negative literal, `~` lazy, infix constructor (`:` / consym), 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 +114,31 @@ Key mappings:
 
 _Newest first._
 
+- **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: