From 6bb99b45c3291767ceb9d683f37a22f7e5696f9c Mon Sep 17 00:00:00 2001
From: Tony Garnock-Jones <tonyg@leastfixedpoint.com>
Date: Wed, 18 Aug 2021 14:04:00 -0400
Subject: [PATCH] fold.py

---
 implementations/python/preserves/__init__.py |  2 ++
 implementations/python/preserves/fold.py     | 17 +++++++++++++++++
 2 files changed, 19 insertions(+)
 create mode 100644 implementations/python/preserves/fold.py

diff --git a/implementations/python/preserves/__init__.py b/implementations/python/preserves/__init__.py
index 9a1f59b..393e2b9 100644
--- a/implementations/python/preserves/__init__.py
+++ b/implementations/python/preserves/__init__.py
@@ -6,5 +6,7 @@ from .error import DecodeError, EncodeError, ShortPacket
 from .binary import Decoder, Encoder, decode, decode_with_annotations, encode
 from .text import Parser, Formatter, parse, parse_with_annotations, stringify
 
+from . import fold
+
 loads = parse
 dumps = stringify
diff --git a/implementations/python/preserves/fold.py b/implementations/python/preserves/fold.py
new file mode 100644
index 0000000..90b1e43
--- /dev/null
+++ b/implementations/python/preserves/fold.py
@@ -0,0 +1,17 @@
+from .values import ImmutableDict, dict_kvs, Embedded, Record
+
+def map_embeddeds(f, v):
+    def walk(v):
+        if isinstance(v, Embedded):
+            return f(v.embeddedValue)
+        elif isinstance(v, (list, tuple)):
+            return tuple(walk(w) for w in v)
+        elif isinstance(v, (set, frozenset)):
+            return frozenset(walk(w) for w in v)
+        elif isinstance(v, dict):
+            return ImmutableDict.from_kvs(walk(w) for w in dict_kvs(v))
+        elif isinstance(v, Record):
+            return Record(walk(v.key), walk(v.fields))
+        else:
+            return v
+    return walk(v)