diff --git a/effectful/ops/syntax.py b/effectful/ops/syntax.py
index f2cc14b8..904e0ba0 100644
--- a/effectful/ops/syntax.py
+++ b/effectful/ops/syntax.py
@@ -5,7 +5,7 @@
 import random
 import types
 import typing
-from collections.abc import Callable
+from collections.abc import Callable, Iterable, Mapping
 from typing import Annotated, Concatenate, Generic, TypeVar
 
 import tree
@@ -1108,6 +1108,39 @@ def trace(value: Callable[P, T]) -> Callable[P, T]:
     return deffn(body, *bound_sig.args, **bound_sig.kwargs)
 
 
+@defop
+def defstream(
+    body: Annotated[T, Scoped[A | B]],
+    streams: Annotated[Mapping[Operation[[], S], Iterable[S]], Scoped[B]],
+) -> Annotated[Iterable[T], Scoped[A]]:
+    """A higher-order operation that represents a for-expression."""
+    raise NotImplementedError
+
+
+@defdata.register(collections.abc.Iterable)
+class _IterableTerm(Generic[T], _BaseTerm[collections.abc.Iterable[T]]):
+    @defop
+    def __iter__(self: collections.abc.Iterable[T]) -> collections.abc.Iterator[T]:
+        if not isinstance(self, Term):
+            return iter(self)
+        else:
+            raise NotImplementedError
+
+
+@defdata.register(collections.abc.Iterator)
+class _IteratorTerm(Generic[T], _IterableTerm[T]):
+    @defop
+    def __next__(self: collections.abc.Iterator[T]) -> T:
+        if not isinstance(self, Term):
+            return next(self)
+        else:
+            raise NotImplementedError
+
+
+iter_ = _IterableTerm.__iter__
+next_ = _IteratorTerm.__next__
+
+
 def syntactic_eq(x: Expr[T], other: Expr[T]) -> bool:
     """Syntactic equality, ignoring the interpretation of the terms.
 
diff --git a/tests/test_ops_syntax.py b/tests/test_ops_syntax.py
index 93402f87..81d0be54 100644
--- a/tests/test_ops_syntax.py
+++ b/tests/test_ops_syntax.py
@@ -1,18 +1,21 @@
 import functools
 import inspect
-from collections.abc import Callable, Mapping
+from collections.abc import Callable, Iterable, Iterator, Mapping
 from typing import Annotated, ClassVar, TypeVar
 
 import pytest
 
 import effectful.handlers.numbers  # noqa: F401
-from effectful.ops.semantics import call, evaluate, fvsof, handler
+from effectful.ops.semantics import call, evaluate, fvsof, handler, typeof
 from effectful.ops.syntax import (
     Scoped,
     _CustomSingleDispatchCallable,
     deffn,
     defop,
+    defstream,
     defterm,
+    iter_,
+    next_,
 )
 from effectful.ops.types import Operation, Term
 
@@ -484,3 +487,56 @@ def _(self, x: bool) -> bool:
     # Test that the method can be called with a handler
     with handler({MyClass.my_singledispatch: lambda self, x: x + 6}):
         assert instance.my_singledispatch(5) == 11
+
+
+def test_defdata_iterable():
+    @defop
+    def cons_iterable(*args: int) -> Iterable[int]:
+        raise NotImplementedError
+
+    tm = cons_iterable(1, 2, 3)
+    assert isinstance(tm, Term)
+    assert isinstance(tm, Iterable)
+    assert issubclass(typeof(tm), Iterable)
+    assert tm.op is cons_iterable
+    assert tm.args == (1, 2, 3)
+
+    tm_iter = iter(tm)
+    assert isinstance(tm_iter, Term)
+    assert isinstance(tm_iter, Iterator)
+    assert issubclass(typeof(tm_iter), Iterator)
+    assert tm_iter.op is iter_
+
+    tm_iter_next = next(tm_iter)
+    assert isinstance(tm_iter_next, Term)
+    # assert isinstance(tm_iter_next, numbers.Number)  # TODO
+    # assert issubclass(typeof(tm_iter_next), numbers.Number)
+    assert tm_iter_next.op is next_
+
+    assert list(tm.args) == [1, 2, 3]
+
+
+def test_defstream_1():
+    x = defop(int, name="x")
+    y = defop(int, name="y")
+    tm = defstream(x() + y(), {x: [1, 2, 3], y: [x() + 1, x() + 2, x() + 3]})
+
+    assert isinstance(tm, Term)
+    assert isinstance(tm, Iterable)
+    assert issubclass(typeof(tm), Iterable)
+    assert tm.op is defstream
+
+    assert x not in fvsof(tm)
+    assert y not in fvsof(tm)
+
+    tm_iter = iter(tm)
+    assert isinstance(tm_iter, Term)
+    assert isinstance(tm_iter, Iterator)
+    assert issubclass(typeof(tm_iter), Iterator)
+    assert tm_iter.op is iter_
+
+    tm_iter_next = next(tm_iter)
+    assert isinstance(tm_iter_next, Term)
+    # assert isinstance(tm_iter_next, numbers.Number)  # TODO
+    # assert issubclass(typeof(tm_iter_next), numbers.Number)
+    assert tm_iter_next.op is next_