scheme: Phase 9 — define-record-type + 9 tests

eval.sx adds the define-record-type syntactic operator:

  (define-record-type NAME
    (CONSTRUCTOR ARG...)
    PREDICATE
    (FIELD ACCESSOR [MUTATOR])...)

Records are tagged dicts:
  {:scm-record TYPE-NAME :fields {FIELD VALUE ...}}

For each record type, the operator binds:
- Constructor: takes the listed ARGs, populates :fields, returns
  the record. Fields not in CONSTRUCTOR ARGs default to nil.
- Predicate: returns true iff its arg is a record of THIS type
  (tag-match via :scm-record).
- Accessor per field: extracts the field value; errors if not
  a record of the right type.
- Mutator per field (optional): sets the field via dict-set!;
  same type-check.

Distinct types are isolated via their tag — point? returns false
on a circle, even if both have the same shape.

9 tests cover: constructor + predicate + accessors, mutator,
distinct-types-via-tag, records as first-class values (in lists,
passed to map/filter), constructor arity errors.

289 total Scheme tests (62+23+49+78+25+20+13+10+9).

lib/scheme/tests/records.sx

@@ -0,0 +1,96 @@
+;; lib/scheme/tests/records.sx — define-record-type.
+
+(define scm-rec-pass 0)
+(define scm-rec-fail 0)
+(define scm-rec-fails (list))
+
+(define
+  scm-rec-test
+  (fn
+    (name actual expected)
+    (if
+      (= actual expected)
+      (set! scm-rec-pass (+ scm-rec-pass 1))
+      (begin
+        (set! scm-rec-fail (+ scm-rec-fail 1))
+        (append! scm-rec-fails {:name name :actual actual :expected expected})))))
+
+(define
+  scm-rec
+  (fn (src) (scheme-eval (scheme-parse src) (scheme-standard-env))))
+
+(define
+  scm-rec-all
+  (fn
+    (src)
+    (scheme-eval-program (scheme-parse-all src) (scheme-standard-env))))
+
+;; ── Basic record: point ─────────────────────────────────────────
+
+(scm-rec-test
+  "point: constructor + predicate"
+  (scm-rec-all
+    "(define-record-type point\n       (make-point x y) point?\n       (x point-x) (y point-y))\n     (point? (make-point 3 4))")
+  true)
+(scm-rec-test
+  "point: accessor x"
+  (scm-rec-all
+    "(define-record-type point\n       (make-point x y) point?\n       (x point-x) (y point-y))\n     (point-x (make-point 3 4))")
+  3)
+(scm-rec-test
+  "point: accessor y"
+  (scm-rec-all
+    "(define-record-type point\n       (make-point x y) point?\n       (x point-x) (y point-y))\n     (point-y (make-point 3 4))")
+  4)
+(scm-rec-test
+  "point: predicate false on number"
+  (scm-rec-all
+    "(define-record-type point\n       (make-point x y) point?\n       (x point-x) (y point-y))\n     (point? 42)")
+  false)
+
+;; ── Mutator ─────────────────────────────────────────────────────
+
+(scm-rec-test
+  "point: mutator"
+  (scm-rec-all
+    "(define-record-type point\n       (make-point x y) point?\n       (x point-x) (y point-y set-point-y!))\n     (define p (make-point 3 4))\n     (set-point-y! p 99)\n     (point-y p)")
+  99)
+
+;; ── Multiple record types are distinct ──────────────────────────
+
+(scm-rec-test
+  "distinct types: point? false on circle"
+  (scm-rec-all
+    "(define-record-type point\n       (make-point x y) point? (x point-x) (y point-y))\n     (define-record-type circle\n       (make-circle r) circle? (r circle-r))\n     (point? (make-circle 5))")
+  false)
+(scm-rec-test
+  "distinct types: circle? true on circle"
+  (scm-rec-all
+    "(define-record-type point\n       (make-point x y) point? (x point-x) (y point-y))\n     (define-record-type circle\n       (make-circle r) circle? (r circle-r))\n     (circle? (make-circle 5))")
+  true)
+
+;; ── Records as first-class values ───────────────────────────────
+
+(scm-rec-test
+  "record in a list"
+  (scm-rec-all
+    "(define-record-type box\n       (make-box v) box? (v box-v))\n     (map box-v (list (make-box 1) (make-box 2) (make-box 3)))")
+  (list 1 2 3))
+
+;; ── Records via map/filter ──────────────────────────────────────
+
+(scm-rec-test
+  "filter records by predicate"
+  (scm-rec-all
+    "(define-record-type box\n       (make-box v) box? (v box-v))\n     (length\n       (filter (lambda (b) (> (box-v b) 5))\n               (list (make-box 1) (make-box 7) (make-box 3) (make-box 10)))))")
+  2)
+
+;; ── Constructor arity errors ────────────────────────────────────
+
+(scm-rec-test
+  "ctor: wrong arity errors"
+  (scm-rec-all
+    "(define-record-type point (make-point x y) point? (x point-x) (y point-y))\n     (guard (e (else 'arity-err)) (make-point 1))")
+  "arity-err")
+
+(define scm-rec-tests-run! (fn () {:total (+ scm-rec-pass scm-rec-fail) :passed scm-rec-pass :failed scm-rec-fail :fails scm-rec-fails}))