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

lib/erlang/parser-expr.sx

@@ -237,6 +237,8 @@
         (er-parse-fun-expr st)
         (er-is? st "keyword" "try")
         (er-parse-try st)
+        (er-is? st "punct" "<<")
+        (er-parse-binary st)
         :else (error
           (str
             "Erlang parse: unexpected "
@@ -576,3 +578,63 @@
           ((guards (if (er-is? st "keyword" "when") (do (er-advance! st) (er-parse-guards st)) (list))))
           (er-expect! st "punct" "->")
           (let ((body (er-parse-body st))) {:pattern pat :body body :class klass :guards guards}))))))
+
+;; ── binary literals / patterns ────────────────────────────────
+;; `<< [Seg {, Seg}] >>` where Seg = Value [: Size] [/ Spec]. Size is
+;; a literal integer (multiple of 8 supported); Spec is `integer`
+;; (default) or `binary` (rest-of-binary tail). Sufficient for the
+;; common `<<A:8, B:16, Rest/binary>>` patterns.
+(define
+  er-parse-binary
+  (fn
+    (st)
+    (er-expect! st "punct" "<<")
+    (cond
+      (er-is? st "punct" ">>")
+      (do (er-advance! st) {:segments (list) :type "binary"})
+      :else (let
+        ((segs (list (er-parse-binary-segment st))))
+        (er-parse-binary-tail st segs)))))
+
+(define
+  er-parse-binary-tail
+  (fn
+    (st segs)
+    (cond
+      (er-is? st "punct" ",")
+      (do
+        (er-advance! st)
+        (append! segs (er-parse-binary-segment st))
+        (er-parse-binary-tail st segs))
+      (er-is? st "punct" ">>")
+      (do (er-advance! st) {:segments segs :type "binary"})
+      :else (error
+        (str
+          "Erlang parse: expected ',' or '>>' in binary, got '"
+          (er-cur-value st)
+          "'")))))
+
+(define
+  er-parse-binary-segment
+  (fn
+    (st)
+    ;; Use `er-parse-primary` for the value so a leading `:` falls
+    ;; through to the segment's size suffix instead of being eaten
+    ;; by `er-parse-postfix-loop` as a `Mod:Fun` remote call.
+    (let
+      ((v (er-parse-primary st)))
+      (let
+        ((size (cond
+                 (er-is? st "punct" ":")
+                 (do (er-advance! st) (er-parse-primary st))
+                 :else nil))
+          (spec (cond
+                  (er-is? st "op" "/")
+                  (do
+                    (er-advance! st)
+                    (let
+                      ((tok (er-cur st)))
+                      (er-advance! st)
+                      (get tok :value)))
+                  :else "integer")))
+        {:size size :spec spec :value v}))))