Allow chained assignment in setv

Author: Kodiologist

NEWS.rst

@@ -1,5 +1,14 @@
 .. default-role:: code
 
+Unreleased
+======================================================================
+
+Supports Python 3.x – Python 3.y
+
+New Features
+------------------------------
+* `setv` now supports chained assignment with `:chain`.
+
 1.1.0 ("Business Hugs", released 2025-05-08)
 ======================================================================
 

docs/api.rst

@@ -270,6 +270,12 @@ Assignment, mutation, and annotation
        (print letter1 letter2 (hy.repr others))
          ; => a b ["c" "d" "e" "f" "g"]
 
+   Finally, as of Hy 1.2.0, you can precede an assignment pair with the keyword ``:chain`` to assign the same value multiple times to each of several targets. This construct compiles to a chained assignment in Python. ::
+
+       (setv :chain [x y z] 0)
+       (print x y z)
+         ; => 0 0 0
+
    See :hy:func:`let` to simulate more traditionally Lispy block-level scoping.
 
 .. hy:macro:: (setx [target value])

hy/core/result_macros.py

@@ -481,23 +481,27 @@ def compile_augassign_expression(compiler, expr, root, target, values):
 # ------------------------------------------------
 
 
-@pattern_macro("setv", [many(maybe_annotated(FORM) + FORM)])
-@pattern_macro("setx", [times(1, 1, SYM + FORM)])
+@pattern_macro("setv", [many(
+    (tag("chained", sym(":chain") + brackets(oneplus(FORM))) |
+        tag("maybe_annotated", maybe_annotated(FORM))) +
+    FORM)])
+@pattern_macro("setx", [times(1, 1, tag("setx", SYM) + FORM)])
 def compile_def_expression(compiler, expr, root, decls):
     if not decls:
         return asty.Constant(expr, value=None)
 
     result = Result()
-    is_assignment_expr = root == "setx"
-    for decl in decls:
-        if is_assignment_expr:
-            ann = None
-            target, value = decl
-        else:
-            (target, ann), value = decl
 
+    for (ttag, target), value in decls:
+        ann = None
+        if ttag == "chained":
+            [target] = target
+        if ttag == "maybe_annotated":
+            target, ann = target
         result += compile_assign(
-            compiler, ann, target, value, is_assignment_expr=is_assignment_expr
+            compiler, ann, target, value,
+            is_assignment_expr = ttag == "setx",
+            chained = ttag == "chained"
         )
     return result
 
@@ -521,7 +525,7 @@ def compile_basic_annotation(compiler, expr, root, target, ann):
 
 
 def compile_assign(
-    compiler, ann, target, value, *, is_assignment_expr=False, let_scope=None
+    compiler, ann, target, value, *, is_assignment_expr=False, chained=False, let_scope=None
 ):
     # Ensure that assignment expressions have a result and no annotation.
     assert not is_assignment_expr or (value is not None and ann is None)
@@ -541,13 +545,15 @@ def compile_assign(
             # Throw away .expr to ensure that (setv ...) returns None.
             result.expr = None
     else:
-        st_target = compiler._storeize(target, compiler.compile(target))
+        st_targets = [
+           compiler._storeize(t, compiler.compile(t))
+           for t in (target if chained else [target])]
 
         if ann is not None:
             ann_result = compiler.compile(ann)
             result = ann_result + result
 
-        target_kwarg = dict(target = st_target)
+        target_kwarg = dict(target = st_targets[0])
         if is_assignment_expr:
             node = asty.NamedExpr
         elif ann is not None:
@@ -559,7 +565,7 @@ def compile_assign(
             )
         else:
             node = asty.Assign
-            target_kwarg = dict(targets = [st_target])
+            target_kwarg = dict(targets = st_targets)
 
         result += node(
             target if hasattr(target, "start_line") else result,

tests/native_tests/setv.hy

@@ -105,3 +105,35 @@
   (an (setv x.eggs "ham"))
   (assert (not (hasattr x "eggs")))
   (assert (= l [["eggs" "ham"]])))
+
+
+(defn test-setv-chain []
+
+  (setv :chain [a b c] 3)
+  (assert (= a b c 3))
+
+  (setv  v1 1  :chain [v2 v3] 2  v4 4)
+  (assert (= v1 1))
+  (assert (= v2 2))
+  (assert (= v3 2))
+  (assert (= v4 4))
+
+  (setv :chain [[y #* z w] x [a b c d]] "abcd")
+  (assert (= [y z w] ["a" ["b" "c"] "d"]))
+  (assert (= x "abcd"))
+  (assert (= [a b c d] ["a" "b" "c" "d"]))
+
+  (setv l (* [0] 5))
+  (setv calls [])
+  (defn f [i]
+    (.append calls [i (list l)])
+    i)
+  (setv :chain
+    [(get l (f 1)) (get l (f 2)) (get l (f 3))]
+    (f 9))
+  (assert (= calls [
+    [9 [0 0 0 0 0]]
+    [1 [0 0 0 0 0]]
+    [2 [0 9 0 0 0]]
+    [3 [0 9 9 0 0]]]))
+  (assert (= l [0 9 9 9 0])))

tests/resources/pydemo.hy

@@ -43,6 +43,9 @@ Call me Ishmael. Some years ago—never mind how long precisely—having little
 (import itertools [cycle])
 (setv mygenexpr (gfor x (cycle [1 2 3]) :if (!= x 2) x))
 
+(setv [unpacked1 #* repacked unpacked2] "WXYZ")
+(setv :chain [chained1 chained2 chained3] 77)
+
 (setv attr-ref str.upper)
 (setv subscript (get "hello" 2))
 (setv myslice (cut "hello" 1 None 2))

tests/test_hy2py.py

@@ -89,6 +89,9 @@ def assert_stuff(m):
     assert type(m.mygenexpr) is type(x for x in [1, 2, 3])
     assert list(itertools.islice(m.mygenexpr, 5)) == [1, 3, 1, 3, 1]
 
+    assert (m.unpacked1, m.repacked, m.unpacked2) == ("W", ["X", "Y"], "Z")
+    assert m.chained1 == m.chained2 == m.chained3 == 77
+
     assert m.attr_ref is str.upper
     assert m.subscript == "l"
     assert m.myslice == "el"