haskell: Phase 14 — record desugar (con-rec → con-def + accessor fun-clauses)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/haskell/desugar.sx

@@ -182,13 +182,13 @@
             ((= tag "sect-right")
               (list :sect-right (nth node 1) (hk-desugar (nth node 2))))
             ((= tag "program")
-              (list :program (map hk-desugar (nth node 1))))
+              (list :program (map hk-desugar (hk-expand-records (nth node 1)))))
             ((= tag "module")
               (list
                 :module (nth node 1)
                 (nth node 2)
                 (nth node 3)
-                (map hk-desugar (nth node 4))))
+                (map hk-desugar (hk-expand-records (nth node 4)))))
             ((= tag "fun-clause")
               (list
                 :fun-clause (nth node 1)
@@ -207,9 +207,98 @@
 
 ;; Convenience — tokenize + layout + parse + desugar.
 (define
-  hk-core
-  (fn (src) (hk-desugar (hk-parse-top src))))
+  hk-record-accessors
+  (fn
+    (cname rec-fields)
+    (let
+      ((n (len rec-fields)) (i 0) (out (list)))
+      (define
+        hk-ra-loop
+        (fn
+          ()
+          (when
+            (< i n)
+            (let
+              ((field (nth rec-fields i)))
+              (let
+                ((fname (first field)) (j 0) (pats (list)))
+                (define
+                  hk-pat-loop
+                  (fn
+                    ()
+                    (when
+                      (< j n)
+                      (begin
+                        (append!
+                          pats
+                          (if
+                            (= j i)
+                            (list "p-var" "__rec_field")
+                            (list "p-wild")))
+                        (set! j (+ j 1))
+                        (hk-pat-loop)))))
+                (hk-pat-loop)
+                (append!
+                  out
+                  (list
+                    "fun-clause"
+                    fname
+                    (list (list "p-con" cname pats))
+                    (list "var" "__rec_field")))
+                (set! i (+ i 1))
+                (hk-ra-loop))))))
+      (hk-ra-loop)
+      out)))
 
 (define
-  hk-core-expr
-  (fn (src) (hk-desugar (hk-parse src))))
+  hk-expand-records
+  (fn
+    (decls)
+    (let
+      ((out (list)))
+      (for-each
+        (fn
+          (d)
+          (cond
+            ((and (list? d) (= (first d) "data"))
+              (let
+                ((dname (nth d 1))
+                  (tvars (nth d 2))
+                  (cons-list (nth d 3))
+                  (deriving (if (> (len d) 4) (nth d 4) (list)))
+                  (new-cons (list))
+                  (accessors (list)))
+                (begin
+                  (for-each
+                    (fn
+                      (c)
+                      (cond
+                        ((= (first c) "con-rec")
+                          (let
+                            ((cname (nth c 1)) (rec-fields (nth c 2)))
+                            (begin
+                              (append!
+                                new-cons
+                                (list
+                                  "con-def"
+                                  cname
+                                  (map (fn (f) (nth f 1)) rec-fields)))
+                              (for-each
+                                (fn (a) (append! accessors a))
+                                (hk-record-accessors cname rec-fields)))))
+                        (:else (append! new-cons c))))
+                    cons-list)
+                  (append!
+                    out
+                    (if
+                      (empty? deriving)
+                      (list "data" dname tvars new-cons)
+                      (list "data" dname tvars new-cons deriving)))
+                  (for-each (fn (a) (append! out a)) accessors))))
+            (:else (append! out d))))
+        decls)
+      out)))
+
+(define hk-core (fn (src) (hk-desugar (hk-parse-top src))))
+
+(define hk-core-expr (fn (src) (hk-desugar (hk-parse src))))

plans/haskell-completeness.md

@@ -249,7 +249,7 @@ No OCaml changes are needed. The view type is fully representable as an SX dict.
 
 - [x] Parser: extend `hk-parse-data` to recognise `{ field :: Type, … }`
   constructor bodies. AST node: `(:con-rec CNAME [(FNAME TYPE) …])`.
-- [ ] Desugar: `:con-rec` → positional `:con-def` plus generated accessor
+- [x] Desugar: `:con-rec` → positional `:con-def` plus generated accessor
   functions `(\rec -> case rec of …)` for each field name.
 - [ ] Record creation `Foo { bar = 1, baz = "x" }` parsed as
   `(:rec-create CON [(FNAME EXPR) …])`. Eval builds the same tagged list as
@@ -313,6 +313,18 @@ No OCaml changes are needed. The view type is fully representable as an SX dict.
 
 _Newest first._
 
+**2026-05-07** — Phase 14 record desugar (`:con-rec` → positional + accessors):
+- New `hk-record-accessors` helper in `desugar.sx` generates one fun-clause
+  per field, pattern-matching on the constructor with wildcards in all other
+  positions.
+- New `hk-expand-records` walks the decls list pre-desugar; `data` decls with
+  `con-rec` get their constructor rewritten to `con-def` (just the types) and
+  accessor fun-clauses appended after the data decl. Other decls pass through.
+- Wired into the `program` and `module` cases of `hk-desugar`. End-to-end:
+  `data Person = Person { name :: String, age :: Int }` + `name (Person "alice" 30)`
+  returns `"alice"`, `age (Person "bob" 25)` returns `25`. No regressions in
+  parse / desugar / deriving.
+
 **2026-05-07** — Phase 14 record parser: `data Foo = Foo { name :: T, … }`:
 - Extended `hk-parse-con-def` to peek for `{` after the constructor name; if
   found, parse `varid :: type` pairs separated by commas, terminate with `}`,