haskell: operator sections + list comprehensions, Phase 1 parser complete (+22 tests, 211/211)

plans/haskell-on-sx.md

@@ -63,8 +63,8 @@ Key mappings:
   - [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
-  - [ ] List comprehensions + operator sections
-- [ ] AST design modelled on GHC's HsSyn at a surface level
+  - [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)
@@ -114,6 +114,38 @@ Key mappings:
 
 _Newest first._
 
+- **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`,