haskell: Phase 17 — import declarations anywhere among top-level decls

hk-collect-module-body previously ran a fixed import-loop at the start
and then a separate decl-loop; merged into a single hk-body-step
dispatcher that routes `import` to the imports list and everything else
to hk-parse-decl. Both call sites (initial step + post-semicolon loop)
use the dispatcher. The eval side reads imports as a list (not by AST
position) so mid-stream imports feed into hk-bind-decls! unchanged.

tests/parse-extras.sx 12 → 17: very-top, mid-stream, post-main,
two-imports-different-positions, unqualified-mid-file. Regression
sweep clean: eval 66/0, exceptions 14/0, typecheck 15/0, records 14/0,
ioref 13/0, map 26/0, set 17/0.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

lib/haskell/desugar.sx

@@ -210,6 +210,7 @@
                 :op (nth node 1)
                 (hk-desugar (nth node 2))
                 (hk-desugar (nth node 3))))
+            ((= tag "type-ann") (hk-desugar (nth node 1)))
             ((= tag "neg") (list :neg (hk-desugar (nth node 1))))
             ((= tag "if")
               (list

lib/haskell/parser.sx

@@ -275,38 +275,47 @@
                             (list :sect-right op-name expr-e))))))
                   (:else
                     (let
-                      ((first-e (hk-parse-expr-inner))
+                      ((first-e (hk-parse-expr-inner)))
-                        (items (list))
-                        (is-tuple false))
-                      (append! items first-e)
-                      (define
-                        hk-tup-loop
-                        (fn
-                          ()
-                          (when
-                            (hk-match? "comma" nil)
-                            (do
-                              (hk-advance!)
-                              (set! is-tuple true)
-                              (append! items (hk-parse-expr-inner))
-                              (hk-tup-loop)))))
-                      (hk-tup-loop)
                       (cond
-                        ((hk-match? "rparen" nil)
+                        ((hk-match? "reservedop" "::")
                           (do
                             (hk-advance!)
-                            (if is-tuple (list :tuple items) first-e)))
+                            (let
+                              ((ann-type (hk-parse-type)))
+                              (hk-expect! "rparen" nil)
+                              (list :type-ann first-e ann-type))))
                         (:else
                           (let
-                            ((op-info2 (hk-section-op-info)))
+                            ((items (list)) (is-tuple false))
+                            (append! items first-e)
+                            (define
+                              hk-tup-loop
+                              (fn
+                                ()
+                                (when
+                                  (hk-match? "comma" nil)
+                                  (do
+                                    (hk-advance!)
+                                    (set! is-tuple true)
+                                    (append! items (hk-parse-expr-inner))
+                                    (hk-tup-loop)))))
+                            (hk-tup-loop)
                             (cond
-                              ((and (not (nil? op-info2)) (not is-tuple) (let ((after2 (hk-peek-at (get op-info2 "len")))) (and (not (nil? after2)) (= (get after2 "type") "rparen"))))
+                              ((hk-match? "rparen" nil)
-                                (let
+                                (do
-                                  ((op-name (get op-info2 "name")))
-                                  (hk-consume-op!)
                                   (hk-advance!)
-                                  (list :sect-left op-name first-e)))
+                                  (if is-tuple (list :tuple items) first-e)))
-                              (:else (hk-err "expected ')' after expression"))))))))))))))
+                              (:else
+                                (let
+                                  ((op-info2 (hk-section-op-info)))
+                                  (cond
+                                    ((and (not (nil? op-info2)) (not is-tuple) (let ((after2 (hk-peek-at (get op-info2 "len")))) (and (not (nil? after2)) (= (get after2 "type") "rparen"))))
+                                      (let
+                                        ((op-name (get op-info2 "name")))
+                                        (hk-consume-op!)
+                                        (hk-advance!)
+                                        (list :sect-left op-name first-e)))
+                                    (:else (hk-err "expected ')' after expression")))))))))))))))))
       (define
         hk-comp-qual-is-gen?
         (fn
@@ -1724,10 +1733,18 @@
                   (= (hk-peek-type) "eof")
                   (hk-match? "vrbrace" nil)
                   (hk-match? "rbrace" nil))))
+            (define
+              hk-body-step
+              (fn
+                ()
+                (cond
+                  ((hk-match? "reserved" "import")
+                    (append! imports (hk-parse-import)))
+                  (:else (append! decls (hk-parse-decl))))))
             (when
               (not (hk-body-at-end?))
               (do
-                (append! decls (hk-parse-decl))
+                (hk-body-step)
                 (define
                   hk-body-loop
                   (fn
@@ -1738,7 +1755,7 @@
                         (hk-advance!)
                         (when
                           (not (hk-body-at-end?))
-                          (append! decls (hk-parse-decl)))
+                          (hk-body-step))
                         (hk-body-loop)))))
                 (hk-body-loop)))
             (list imports decls))))

lib/haskell/tests/parse-extras.sx

@@ -0,0 +1,102 @@
+;; Phase 17 — parser polish unit tests.
+
+(hk-test
+  "type-ann: literal int annotated"
+  (hk-deep-force (hk-run "main = (42 :: Int)"))
+  42)
+
+(hk-test
+  "type-ann: arithmetic annotated"
+  (hk-deep-force (hk-run "main = (1 + 2 :: Int)"))
+  3)
+
+(hk-test
+  "type-ann: function arg annotated"
+  (hk-deep-force
+    (hk-run "f x = x + 1\nmain = f (1 :: Int)"))
+  2)
+
+(hk-test
+  "type-ann: string annotated"
+  (hk-deep-force (hk-run "main = (\"hi\" :: String)"))
+  "hi")
+
+(hk-test
+  "type-ann: bool annotated"
+  (hk-deep-force (hk-run "main = (True :: Bool)"))
+  (list "True"))
+
+(hk-test
+  "type-ann: tuple annotated"
+  (hk-deep-force (hk-run "main = ((1, 2) :: (Int, Int))"))
+  (list "Tuple" 1 2))
+
+(hk-test
+  "type-ann: nested annotation in arithmetic"
+  (hk-deep-force (hk-run "main = (1 :: Int) + (2 :: Int)"))
+  3)
+
+(hk-test
+  "type-ann: function-typed annotation passes through eval"
+  (hk-deep-force
+    (hk-run "main = let f = ((\\x -> x + 1) :: Int -> Int) in f 5"))
+  6)
+
+(hk-test
+  "no regression: plain parens still work"
+  (hk-deep-force (hk-run "main = (5)"))
+  5)
+
+(hk-test
+  "no regression: 3-tuple still works"
+  (hk-deep-force (hk-run "main = (1, 2, 3)"))
+  (list "Tuple" 1 2 3))
+
+(hk-test
+  "no regression: section-left still works"
+  (hk-deep-force (hk-run "main = (3 +) 4"))
+  7)
+
+(hk-test
+  "no regression: section-right still works"
+  (hk-deep-force (hk-run "main = (+ 3) 4"))
+  7)
+
+(hk-test
+  "import: still works as the very first decl"
+  (hk-deep-force
+    (hk-run "import qualified Data.IORef as I
+main = do { r <- I.newIORef 7; I.readIORef r }"))
+  (list "IO" 7))
+
+(hk-test
+  "import: between decls — after main"
+  (hk-deep-force
+    (hk-run "main = do { r <- I.newIORef 11; I.readIORef r }
+import qualified Data.IORef as I"))
+  (list "IO" 11))
+
+(hk-test
+  "import: between two decls — uses helper after import"
+  (hk-deep-force
+    (hk-run "f x = x + 100
+import qualified Data.IORef as I
+main = do { r <- I.newIORef 5; I.modifyIORef r f; I.readIORef r }"))
+  (list "IO" 105))
+
+(hk-test
+  "import: two imports in different positions"
+  (hk-deep-force
+    (hk-run "import qualified Data.IORef as I
+helper x = x * 2
+import qualified Data.Map as M
+main = do { r <- I.newIORef (helper 21); I.readIORef r }"))
+  (list "IO" 42))
+
+(hk-test
+  "import: unqualified, mid-file"
+  (hk-deep-force
+    (hk-run "go x = x
+import Data.IORef
+main = go 9"))
+  9)

lib/haskell/tests/typecheck.sx

@@ -16,15 +16,18 @@
       true)))
 
 ;; ─── Valid programs pass through ─────────────────────────────────────────────
-(hk-test "typed ok: simple arithmetic" (hk-run-typed "main = 1 + 2") 3)
+(hk-test "typed ok: simple arithmetic"
+  (hk-deep-force (hk-run-typed "main = 1 + 2")) 3)
 
-(hk-test "typed ok: boolean" (hk-run-typed "main = True") (list "True"))
+(hk-test "typed ok: boolean"
+  (hk-deep-force (hk-run-typed "main = True")) (list "True"))
 
-(hk-test "typed ok: let binding" (hk-run-typed "main = let x = 1 in x + 2") 3)
+(hk-test "typed ok: let binding"
+  (hk-deep-force (hk-run-typed "main = let x = 1 in x + 2")) 3)
 
 (hk-test
   "typed ok: two independent fns"
-  (hk-run-typed "f x = x + 1\nmain = f 5")
+  (hk-deep-force (hk-run-typed "f x = x + 1\nmain = f 5"))
   6)
 
 ;; ─── Untypeable programs are rejected ────────────────────────────────────────
@@ -76,7 +79,7 @@
 
 (hk-test
   "run-typed sig ok: Int declared matches"
-  (hk-run-typed "main :: Int\nmain = 1 + 2")
+  (hk-deep-force (hk-run-typed "main :: Int\nmain = 1 + 2"))
   3)
 
 {:fails hk-test-fails :pass hk-test-pass :fail hk-test-fail}

plans/haskell-completeness.md

@@ -316,11 +316,11 @@ No OCaml changes are needed. The view type is fully representable as an SX dict.
 Real Haskell programs use these on every page; closing the gaps unblocks
 larger conformance programs and removes one-line workarounds in test sources.
 
-- [ ] Type annotations in expressions: `(x :: Int)`, `f (1 :: Int)`,
+- [x] Type annotations in expressions: `(x :: Int)`, `f (1 :: Int)`,
   `return (42 :: Int)`. Parser currently rejects `::` in `aexp` position;
   desugar should drop the annotation (we have no inference at this layer
   yet, so it's a parse-only pass-through).
-- [ ] `import` declarations anywhere at the start of a module — currently
+- [x] `import` declarations anywhere at the start of a module — currently
   only the very-top-of-file form is recognised. Real test programs that
   mix prelude code with `import qualified Data.IORef` need this.
 - [ ] Multi-line top-level `where` blocks (`where { ... }` with explicit
@@ -359,10 +359,100 @@ that to single-digit minutes.
 - [ ] Verify the scoreboard output is byte-identical to the old per-process
   driver, then keep the per-process path as `--isolated` for debugging.
 
+### Phase 20 — Close Algorithm W gaps
+
+`lib/haskell/infer.sx` already implements core HM (TVar/TCon/TArr/TApp/TTuple/
+TScheme, substitution, occurs-check unification, instantiate/generalize, let-
+polymorphism). 75 inference unit tests + 15 typecheck integration tests pass.
+The remaining gaps that block typing real programs:
+
+- [ ] `case` expressions in `hk-w`. Needs to infer scrutinee type, then for
+  each `(:alt pat body)` infer the pattern's binding env (extending
+  `hk-w-pat`) and unify body types across alts.
+- [ ] `do` notation: extend `hk-type-env0` with `return :: a -> IO a`,
+  `(>>=) :: IO a -> (a -> IO b) -> IO b`, `(>>) :: IO a -> IO b -> IO b`,
+  and primitive IO actions (`putStrLn :: String -> IO ()`,
+  `getLine :: IO String`, etc.). May need a `TApp (TCon "IO") a` shape.
+- [ ] Record-accessor desugaring leaves `__rec_field` placeholder visible to
+  inference. Either skip generated accessor clauses during `hk-infer-prog`
+  or rewrite the desugar to produce a typed shape.
+- [ ] Type annotations in expressions `(x :: Int)` (parser also needed; see
+  Phase 17). Infer should unify the inferred type with the annotation.
+- [ ] Tests in `lib/haskell/tests/infer-extras.sx` (≥ 10) covering the
+  above shapes.
+
+### Phase 21 — Type classes (Eq, Ord, Num, Show)
+
+The evaluator already implements typeclass dispatch via dict-passing
+(`__default__ClassName_method` + per-instance dicts). The type system
+ignores `class` and `instance` decls. Closing this means HM with
+constraints (qualified types `[ClassName var] => type`).
+
+- [ ] Extend the type representation: `(TQual CONSTRAINTS TYPE)` where
+  `CONSTRAINTS = [(class-name . type-arg), …]`.
+- [ ] Generalize → `forall vars. preds => type`; instantiate → fresh-rename
+  vars in both preds and type.
+- [ ] During inference, when a primitive operator that needs a class is
+  used (e.g. `+`), emit a constraint `(Num t)`; collect constraints in
+  the substitution-threading.
+- [ ] At let-generalization, simplify constraints (defaulting for `Num`
+  literals → `Int`; entailment via known instances).
+- [ ] `class` declarations register members with their qualified type;
+  `instance` declarations register a witness.
+- [ ] At top-level, if any unsolvable constraint remains → type error
+  ("No instance for X").
+- [ ] Tests in `lib/haskell/tests/typeclasses.sx` (≥ 12 covering Eq, Ord,
+  Num overloading, show on instances, instance ambiguity rejection).
+
+### Phase 22 — Typecheck-then-run as the default
+
+- [ ] Replace `hk-run` with a typecheck-first variant in the conformance
+  driver, or run conformance twice (once typed, once untyped) and report
+  both pass-rates in `scoreboard.md`.
+- [ ] Investigate which existing 36 programs are untypeable due to gaps
+  closed in Phase 20-21 vs genuinely dynamically-typed; aim for ≥ 30/36
+  programs typechecking before committing to the swap.
+- [ ] If swap is committed, retire `hk-run` callsites in tests in favour
+  of `hk-run-typed`; keep the untyped path available for parser/eval
+  development against in-progress features.
+
 ## Progress log
 
 _Newest first._
 
+**2026-05-10** — Phase 17 second box: `import` declarations anywhere among
+top-level decls. `hk-collect-module-body` previously ran a fixed
+import-loop at the start, then a separate decl-loop; merged into a single
+`hk-body-step` dispatcher that routes `import` to the imports list and
+everything else to `hk-parse-decl`. Each call site (initial step + post-
+semicolon loop) now uses the dispatcher. Imports collected mid-stream
+still feed into `hk-bind-decls!` correctly because the eval side reads
+them via the imports list, not by AST position. tests/parse-extras.sx
+12 → 17 covering very-top, mid-stream, post-main, two-imports-different-
+positions, and unqualified mid-file. Regression: eval 66/0, exceptions
+14/0, typecheck 15/0, records 14/0, ioref 13/0, map 26/0, set 17/0.
+
+**2026-05-08** — Phase 17 first box: expression type annotations `(x :: Int)`,
+`f (1 :: Int)`, `(\x -> x+1) :: Int -> Int`. Parser's `hk-parse-parens`
+gains a `::` arm after the first inner expression: consume `::`, parse a
+type via the existing `hk-parse-type`, expect `)`, emit `(:type-ann EXPR
+TYPE)`. Desugar drops the annotation — `:type-ann E _ → (hk-desugar E)` —
+since the existing eval path has no type-directed dispatch; Phase 20 will
+let inference consume the annotation. tests/parse-extras.sx 12/12; eval,
+exceptions, typecheck, records, ioref still clean.
+
+**2026-05-08** — Plan extends with Phases 20-22 (HM type system). Discovered
+during planning that `lib/haskell/infer.sx` already lands core Algorithm W
+(75 inference unit tests pass; let-polymorphism, sig checking, error
+reporting via `hk-expr->brief`). Fixed five regressing tests in
+`lib/haskell/tests/typecheck.sx` that compared an unforced thunk against
+the expected value — added `hk-deep-force` around `hk-run-typed` to match
+the existing untyped-path convention. typecheck.sx now 15/15.
+Phase 20 captures the remaining Algorithm W gaps (case, do, record
+accessors, expression annotations); Phase 21 captures type classes with
+qualified types; Phase 22 captures the integration step (typecheck-then-run
+across conformance).
+
 **2026-05-08** — Phase 16 Exception handling complete (6 ops + module wiring +
 14 unit tests + 2 conformance programs). `hk-bind-exceptions!` in `eval.sx`
 registers `throwIO`, `throw`, `evaluate`, `catch`, `try`, `handle`, and