erlang: binary pattern matching <<...>> (+21 tests)

lib/erlang/tests/eval.sx

@@ -937,6 +937,63 @@
   (nm (nth (get (get (ev "[{ok, X} || X <- [a, b]]") :head) :elements) 0))
   "ok")
 
+;; ── binary literals / patterns ────────────────────────────────
+(er-eval-test "binary tag"
+  (get (ev "<<>>") :tag) "binary")
+(er-eval-test "is_binary empty" (nm (ev "is_binary(<<>>)")) "true")
+(er-eval-test "is_binary 3 bytes"
+  (nm (ev "is_binary(<<1, 2, 3>>)")) "true")
+(er-eval-test "is_binary list" (nm (ev "is_binary([1, 2])")) "false")
+(er-eval-test "byte_size 0" (ev "byte_size(<<>>)") 0)
+(er-eval-test "byte_size 3" (ev "byte_size(<<1, 2, 3>>)") 3)
+(er-eval-test "byte_size 16-bit" (ev "byte_size(<<256:16>>)") 2)
+(er-eval-test "byte_size 32-bit" (ev "byte_size(<<999999:32>>)") 4)
+
+;; Match
+(er-eval-test "match single byte"
+  (ev "<<X>> = <<7>>, X") 7)
+(er-eval-test "match X:8"
+  (ev "<<X:8>> = <<200>>, X") 200)
+(er-eval-test "match 16-bit decode"
+  (ev "<<X:16>> = <<1, 0>>, X") 256)
+(er-eval-test "match 16-bit hi byte"
+  (ev "<<X:16>> = <<2, 1>>, X") 513)
+(er-eval-test "match A:8 B:16"
+  (ev "<<A:8, B:16>> = <<1, 0, 2>>, A + B") 3)
+(er-eval-test "match three 8-bit"
+  (ev "<<A, B, C>> = <<1, 2, 3>>, A + B + C") 6)
+
+;; Tail binary
+(er-eval-test "tail rest size"
+  (ev "<<_:8, Rest/binary>> = <<1, 2, 3, 4>>, byte_size(Rest)") 3)
+(er-eval-test "tail rest content"
+  (ev "<<_:8, Rest/binary>> = <<1, 2, 3, 4>>, <<X:8, _/binary>> = Rest, X") 2)
+
+;; Match failure
+(er-eval-test "size mismatch fails"
+  (do
+    (ev "P = spawn(fun () -> <<X:8, Y:8>> = <<1>>, ok end), receive after 0 -> ok end")
+    (let ((reason (er-proc-field (er-mk-pid 1) :exit-reason)))
+      (cond
+        (er-tuple? reason) (nm (nth (get reason :elements) 0))
+        (er-atom? reason) (get reason :name)
+        :else nil)))
+  "badmatch")
+
+;; Equality
+(er-eval-test "binary =:= self"
+  (nm (ev "B = <<1, 2, 3>>, B =:= B")) "true")
+(er-eval-test "binary =:= same"
+  (nm (ev "<<1, 2>> =:= <<1, 2>>")) "true")
+(er-eval-test "binary =/= different"
+  (nm (ev "<<1, 2>> =:= <<1, 3>>")) "false")
+
+;; Construction with computed value
+(er-eval-test "build with var"
+  (ev "X = 42, byte_size(<<X>>)") 1)
+(er-eval-test "build with size var"
+  (ev "X = 7, byte_size(<<X:16>>)") 2)
+
 (define
   er-eval-test-summary
   (str "eval " er-eval-test-pass "/" er-eval-test-count))