1 files changed, 150 insertions, 0 deletions
diff --git a/third_party/bazel/rules_haskell/haskell/private/set.bzl b/third_party/bazel/rules_haskell/haskell/private/set.bzl
new file mode 100644
index 000000000000..f5c6220f79d6
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+++ b/third_party/bazel/rules_haskell/haskell/private/set.bzl
@@ -0,0 +1,150 @@
+"""Immutable sets that support efficient merging, traversal, and membership
+check.
+"""
+
+def _empty():
+    """Create an empty set.
+
+    Returns:
+      set, new empty set.
+    """
+    return struct(_set_items = dict())
+
+def _singleton(e):
+    """Create a set with single element `e` inside.
+
+    Args:
+      e: The element to put in the set.
+
+    Returns:
+      set, new set.
+    """
+    r = dict()
+    r[e] = None
+    return struct(_set_items = r)
+
+def _is_member(s, e):
+    """Return true if `e` is in the set `s`.
+
+    Args:
+      s: The set to inspect.
+      e: The element to search for.
+
+    Result:
+      Bool, true if `e` is in `s`, false otherwise.
+    """
+    return e in s._set_items
+
+def _insert(s, e):
+    """Insert an element into the set.
+
+    Args:
+      s: Set to insert new element into.
+      e: The element to insert.
+
+    Result:
+      A copy of set `s` with `s` element added.
+    """
+    r = dict(s._set_items)
+    r[e] = None
+    return struct(_set_items = r)
+
+def _mutable_insert(s, e):
+    """The same as `set.insert`, but modifies the first argument in place.
+
+    Args:
+      s: Set to insert new element into.
+      e: The element to insert.
+
+    Result:
+      set `s` with `s` element added.
+    """
+    s._set_items[e] = None
+    return s
+
+def _union(s0, s1):
+    """Return union of two sets.
+
+    Args:
+      s0: One set.
+      s1: Another set.
+
+    Result:
+      set, union of the two sets.
+    """
+    r = dict(s0._set_items)
+    r.update(s1._set_items)
+    return struct(_set_items = r)
+
+def _mutable_union(s0, s1):
+    """Modify set `s0` adding elements from `s1` to it.
+
+    Args:
+      s0: One set.
+      s1: Another set.
+
+    Result:
+      set, union of the two sets.
+    """
+    s0._set_items.update(s1._set_items)
+    return s0
+
+def _map(s, f):
+    """Map elements of given set using a function.
+
+    Args:
+      s: Original set.
+      f: Function to apply to elements of the set.
+
+    Result:
+      set with elements obtained by application of function `f` to the
+      elements of `s`.
+    """
+    return struct(_set_items = {f(x): None for x in s._set_items.keys()})
+
+def _from_list(l):
+    """Create a set containing elements from given list.
+
+    Args:
+      l: List, source of the elements for the new set.
+
+    Result:
+      set containing elements from given list.
+    """
+    return (struct(_set_items = {x: None for x in l}))
+
+def _to_list(s):
+    """Convert set into a list of its elements.
+
+    Args:
+      s: Set to convert.
+
+    Returns:
+      List of elements of the set.
+    """
+    return s._set_items.keys()
+
+def _to_depset(s):
+    """Similar to `set.to_list`, but produces a depset.
+
+    Args:
+      s: Set to convert.
+
+    Returns:
+      Depset of elements from the set.
+    """
+    return depset(_to_list(s))
+
+set = struct(
+    empty = _empty,
+    singleton = _singleton,
+    is_member = _is_member,
+    insert = _insert,
+    mutable_insert = _mutable_insert,
+    union = _union,
+    mutable_union = _mutable_union,
+    map = _map,
+    from_list = _from_list,
+    to_list = _to_list,
+    to_depset = _to_depset,
+)