haskell: deriving (Eq, Show) for ADTs (+11 tests, 565/565)

Parser parses optional deriving clause; only appended to AST when non-empty.
hk-bind-decls! data arm generates dictShow_Con / dictEq_Con per constructor.
hk-binop == and /= now deep-force both sides (SX dict equality is by
reference — two thunks wrapping the same value compared as not-equal without
this). Three token-type fixes in the deriving parser (lparen/rparen/comma,
not "special").

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

lib/haskell/eval.sx

@@ -459,8 +459,9 @@
       ((= op "-") (- lv rv))
       ((= op "*") (* lv rv))
       ((= op "/") (/ lv rv))
-      ((= op "==") (hk-of-bool (= lv rv)))
+      ((= op "==") (hk-of-bool (= (hk-deep-force lv) (hk-deep-force rv))))
-      ((= op "/=") (hk-of-bool (not (= lv rv))))
+      ((= op "/=")
+        (hk-of-bool (not (= (hk-deep-force lv) (hk-deep-force rv)))))
       ((= op "<") (hk-of-bool (< lv rv)))
       ((= op "<=") (hk-of-bool (<= lv rv)))
       ((= op ">") (hk-of-bool (> lv rv)))
@@ -778,6 +779,67 @@
                     env
                     (str "dict" cls "_" (hk-type-to-runtime-key type-str))
                     inst-dict))))
+            ((= (first d) "data")
+              (let
+                ((deriving-list (if (> (len d) 4) (nth d 4) (list))))
+                (when
+                  (not (empty? deriving-list))
+                  (let
+                    ((cons-list (nth d 3)))
+                    (for-each
+                      (fn
+                        (cls)
+                        (for-each
+                          (fn
+                            (cdef)
+                            (let
+                              ((con-name (nth cdef 1)))
+                              (cond
+                                ((= cls "Show")
+                                  (let
+                                    ((inst-dict (dict)))
+                                    (dict-set!
+                                      inst-dict
+                                      "show"
+                                      (hk-mk-lazy-builtin "show" hk-show-val 1))
+                                    (dict-set!
+                                      env
+                                      (str "dictShow_" con-name)
+                                      inst-dict)))
+                                ((= cls "Eq")
+                                  (let
+                                    ((inst-dict (dict)))
+                                    (dict-set!
+                                      inst-dict
+                                      "=="
+                                      (hk-mk-builtin
+                                        "=="
+                                        (fn
+                                          (x y)
+                                          (hk-of-bool
+                                            (=
+                                              (hk-deep-force x)
+                                              (hk-deep-force y))))
+                                        2))
+                                    (dict-set!
+                                      inst-dict
+                                      "/="
+                                      (hk-mk-builtin
+                                        "/="
+                                        (fn
+                                          (x y)
+                                          (hk-of-bool
+                                            (not
+                                              (=
+                                                (hk-deep-force x)
+                                                (hk-deep-force y)))))
+                                        2))
+                                    (dict-set!
+                                      env
+                                      (str "dictEq_" con-name)
+                                      inst-dict))))))
+                          cons-list))
+                      deriving-list)))))
             (:else nil)))
         decls)
       (let

lib/haskell/parser.sx

@@ -1250,7 +1250,8 @@
           (let
             ((name (get (hk-advance!) "value"))
               (tvars (hk-parse-tvars))
-              (cons-list (list)))
+              (cons-list (list))
+              (deriving-list (list)))
             (when
               (hk-match? "reservedop" "=")
               (do
@@ -1267,7 +1268,34 @@
                         (append! cons-list (hk-parse-con-def))
                         (hk-dc-loop)))))
                 (hk-dc-loop)))
-            (list :data name tvars cons-list))))
+            (when
+              (hk-match? "reserved" "deriving")
+              (do
+                (hk-advance!)
+                (cond
+                  ((hk-match? "lparen" nil)
+                    (do
+                      (hk-advance!)
+                      (define
+                        hk-der-loop
+                        (fn
+                          ()
+                          (when
+                            (hk-match? "conid" nil)
+                            (do
+                              (append!
+                                deriving-list
+                                (get (hk-advance!) "value"))
+                              (when (hk-match? "comma" nil) (hk-advance!))
+                              (hk-der-loop)))))
+                      (hk-der-loop)
+                      (hk-expect! "rparen" nil)))
+                  ((hk-match? "conid" nil)
+                    (append! deriving-list (get (hk-advance!) "value"))))))
+            (if
+              (empty? deriving-list)
+              (list :data name tvars cons-list)
+              (list :data name tvars cons-list deriving-list)))))
       (define
         hk-parse-class
         (fn

lib/haskell/tests/deriving.sx

@@ -0,0 +1,84 @@
+;; deriving.sx — tests for deriving (Eq, Show) on ADTs.
+
+;; ─── Show ────────────────────────────────────────────────────────────────────
+
+(hk-test
+  "deriving Show: nullary constructor"
+  (hk-deep-force
+    (hk-run "data Color = Red | Green | Blue deriving (Show)\nmain = show Red"))
+  "Red")
+
+(hk-test
+  "deriving Show: constructor with arg"
+  (hk-deep-force
+    (hk-run "data Wrapper = Wrap Int deriving (Show)\nmain = show (Wrap 42)"))
+  "(Wrap 42)")
+
+(hk-test
+  "deriving Show: nested constructors"
+  (hk-deep-force
+    (hk-run
+      "data Tree = Leaf | Node Int Tree Tree deriving (Show)\nmain = show (Node 1 Leaf Leaf)"))
+  "(Node 1 Leaf Leaf)")
+
+(hk-test
+  "deriving Show: second constructor"
+  (hk-deep-force
+    (hk-run
+      "data Color = Red | Green | Blue deriving (Show)\nmain = show Green"))
+  "Green")
+
+;; ─── Eq ──────────────────────────────────────────────────────────────────────
+
+(hk-test
+  "deriving Eq: same constructor"
+  (hk-deep-force
+    (hk-run
+      "data Color = Red | Green | Blue deriving (Eq)\nmain = show (Red == Red)"))
+  "True")
+
+(hk-test
+  "deriving Eq: different constructors"
+  (hk-deep-force
+    (hk-run
+      "data Color = Red | Green | Blue deriving (Eq)\nmain = show (Red == Blue)"))
+  "False")
+
+(hk-test
+  "deriving Eq: /= same"
+  (hk-deep-force
+    (hk-run
+      "data Color = Red | Green | Blue deriving (Eq)\nmain = show (Red /= Red)"))
+  "False")
+
+(hk-test
+  "deriving Eq: /= different"
+  (hk-deep-force
+    (hk-run
+      "data Color = Red | Green | Blue deriving (Eq)\nmain = show (Red /= Blue)"))
+  "True")
+
+;; ─── combined Eq + Show ───────────────────────────────────────────────────────
+
+(hk-test
+  "deriving Eq Show: combined in parens"
+  (hk-deep-force
+    (hk-run
+      "data Shape = Circle Int | Square Int deriving (Eq, Show)\nmain = show (Circle 5)"))
+  "(Circle 5)")
+
+(hk-test
+  "deriving Eq Show: eq on constructor with arg"
+  (hk-deep-force
+    (hk-run
+      "data Shape = Circle Int | Square Int deriving (Eq, Show)\nmain = show (Circle 3 == Circle 3)"))
+  "True")
+
+(hk-test
+  "deriving Eq Show: different constructors with args"
+  (hk-deep-force
+    (hk-run
+      "data Shape = Circle Int | Square Int deriving (Eq, Show)\nmain = show (Circle 3 == Square 3)"))
+  "False")
+
+{:fails hk-test-fails :pass hk-test-pass :fail hk-test-fail}

plans/haskell-on-sx.md

@@ -102,7 +102,7 @@ Key mappings:
 - [x] `class` / `instance` declarations
 - [x] Dictionary-passing elaborator: inserts dict args at call sites
 - [x] Standard classes: `Eq`, `Ord`, `Show`, `Num`, `Functor`, `Monad`, `Applicative`
-- [ ] `deriving (Eq, Show)` for ADTs
+- [x] `deriving (Eq, Show)` for ADTs
 
 ### Phase 6 — real IO + Prelude completion
 - [ ] Real `IO` monad backed by `perform`/`resume`
@@ -114,6 +114,22 @@ Key mappings:
 
 _Newest first._
 
+- **2026-05-06** — Phase 5 `deriving (Eq, Show)`. Parser: `hk-parse-data` now
+  optionally parses a `deriving (Class1, Class2)` or `deriving Class` clause
+  after constructor definitions; result appended as 5th element only when
+  non-empty (no AST churn for existing decls). Three token-type fixes: the
+  deriving clause used `"special"` for `(`, `)`, `,` but the tokenizer
+  produces `"lparen"`, `"rparen"`, `"comma"`. Eval: `hk-bind-decls!` `data`
+  arm generates `dictShow_{Con}` and `dictEq_{Con}` dicts for each constructor
+  that appears in a `deriving` list. `Show` delegates to `hk-show-val` (lazy).
+  `Eq` needed structural equality — `hk-binop "=="` and `/=` now call
+  `hk-deep-force` on both sides before `=` (SX dict equality is by reference,
+  so two thunks wrapping the same number compared as not-equal without this).
+  11 new tests in `lib/haskell/tests/deriving.sx`: nullary Show, constructor
+  with arg, nested, second constructor, Eq same/different constructor, `/=`
+  same/different, combined `(Eq, Show)`, Eq with args, different constructors
+  with args. 565/565 green.
+
 - **2026-05-06** — Phase 5 standard classes. Prelude extended: `foldr`, `foldl`,
   `foldl1`, `foldr1`, `zip`, `reverse`, `elem`, `notElem`, `any`, `all`, `and`,
   `or`, `sum`, `product`, `maximum`, `minimum`, `compare`, `min`, `max`,