1 files changed, 25 insertions, 0 deletions
diff --git a/tests/concepts/tmonoid.nim b/tests/concepts/tmonoid.nim
new file mode 100644
index 000000000..e0e19adbc
--- /dev/null
+++ b/tests/concepts/tmonoid.nim
@@ -0,0 +1,25 @@
+discard """
+  output: '''true'''
+"""
+
+# bug #3686
+
+type Monoid = concept x, y
+  x + y is type(x)
+  type(z(type(x))) is type(x)
+
+proc z(x: typedesc[int]): int = 0
+
+echo(int is Monoid)
+
+# https://github.com/nim-lang/Nim/issues/8126
+type AdditiveMonoid* = concept x, y, type T
+  x + y is T
+
+  # some redundant checks to test an alternative approaches:
+  type TT = type(x)
+  x + y is type(x)
+  x + y is TT
+
+doAssert(1 is AdditiveMonoid)
+