core: move binding macro to overlay

Phase 3 batch 6 (jolt-1j0). binding installs an array-map var->value thread
frame and restores it on exit via try/finally. Dynamic rebinding is seen by
called fns. This completes the cleanly-portable safe macros (19 total).

conformance 228/228 x3, full suite green.

jolt-core/clojure/core/30-macros.clj

@@ -107,6 +107,15 @@
                       [] fnspecs)]
     `(let* [~@binds] ~@body)))
 
+;; Dynamic binding: install a thread-binding frame of var->value (array-map keeps
+;; var-get happy, unlike a phm), restore on exit.
+(defmacro binding [bindings & body]
+  (let [pairs (reduce (fn [acc p] (conj (conj acc `(var ~(first p))) (second p)))
+                      [] (partition 2 bindings))]
+    `(let* [frame# (array-map ~@pairs)]
+       (push-thread-bindings frame#)
+       (try (do ~@body) (finally (pop-thread-bindings))))))
+
 ;; condp: clauses are test-expr result-expr, or test-expr :>> result-fn (calls
 ;; result-fn on the truthy (pred test-expr value)); a lone trailing expr is the
 ;; default. The recursive emit builds a nested if chain.

src/jolt/core.janet

@@ -2264,31 +2264,6 @@
 
 (defn core-intern [ns-name sym-name val] val)
 
-(defn core-binding
-  "Macro: (binding [var val ...] body...)
-  Uses array-map (plain struct) to store binding frame
-  to avoid PHM get() incompatibility with var-get."
-  [bindings & body]
-  (def frame-pairs @[])
-  (var i 0)
-  (let [n (length bindings)]
-    (while (< i n)
-      (array/push frame-pairs
-        @[{:jolt/type :symbol :ns nil :name "var"} (in bindings i)])
-      (array/push frame-pairs (in bindings (+ i 1)))
-      (+= i 2)))
-  (def hm-form (array/insert frame-pairs 0
-    {:jolt/type :symbol :ns nil :name "array-map"}))
-  @[{:jolt/type :symbol :ns nil :name "let*"}
-    [{:jolt/type :symbol :ns nil :name "frame"} hm-form]
-    @[{:jolt/type :symbol :ns nil :name "push-thread-bindings"}
-      {:jolt/type :symbol :ns nil :name "frame"}]
-    @[{:jolt/type :symbol :ns nil :name "try"}
-      @[{:jolt/type :symbol :ns nil :name "do"} ;body]
-      @[{:jolt/type :symbol :ns nil :name "finally"}
-        @[{:jolt/type :symbol :ns nil :name "pop-thread-bindings"}]]]])
-
-
 (defn- defn->def
   "Shared expansion for defn/defn-: (name doc-string? attr-map? params body...)
   or (name doc-string? attr-map? ([params] body)... attr-map?) -> (def name (fn* ...))."
@@ -3695,7 +3670,6 @@
     "alter-meta!" core-alter-meta!
     "reset-meta!" core-reset-meta!
     "intern" core-intern
-    "binding" core-binding
     "push-thread-bindings" core-push-thread-bindings
     "pop-thread-bindings" core-pop-thread-bindings
     # Dynamic vars — stubs for SCI bootstrap
@@ -3710,7 +3684,7 @@
 (defn core-macro-names
   "Set of core binding names that are macros."
   []
-  @{"and" true "or" true "cond" true "case" true "for" true "when" true "when-not" true "when-let" true "defn" true "defn-" true "declare" true "fn" true "let" true "loop" true "defrecord" true "defprotocol" true "extend-type" true "extend-protocol" true "extend" true "reify" true "proxy" true "definterface" true "binding" true "lazy-seq" true "lazy-cat" true "cond->" true "->" true "->>" true "doseq" true})
+  @{"and" true "or" true "cond" true "case" true "for" true "when" true "when-not" true "when-let" true "defn" true "defn-" true "declare" true "fn" true "let" true "loop" true "defrecord" true "defprotocol" true "extend-type" true "extend-protocol" true "extend" true "reify" true "proxy" true "definterface" true "lazy-seq" true "lazy-cat" true "cond->" true "->" true "->>" true "doseq" true})
 
 (def init-core!
   (fn [& args]

test/spec/macros-spec.janet

@@ -68,4 +68,7 @@
   ["condp match"         ":two"   "(condp = 2 1 :one 2 :two 3 :three)"]
   ["condp default"       ":else"  "(condp = 9 1 :one 2 :two :else)"]
   ["condp :>> form"      "\"got 2\"" "(condp some [1 2 3] #{0 9} :>> (fn [x] (str \"got \" x)) #{2 6} :>> (fn [x] (str \"got \" x)))"]
-  ["condp no match"      ":threw" "(try (condp = 9 1 :one) (catch :default e :threw))"])
+  ["condp no match"      ":threw" "(try (condp = 9 1 :one) (catch :default e :threw))"]
+  ["binding rebinds"     "99"     "(do (def ^:dynamic *bx* 10) (binding [*bx* 99] *bx*))"]
+  ["binding restores"    "10"     "(do (def ^:dynamic *by* 10) (binding [*by* 99] *by*) *by*)"]
+  ["binding seen by fn"  "7"      "(do (def ^:dynamic *bz* 0) (defn rdz [] *bz*) (binding [*bz* 7] (rdz)))"])