generic types can be used like type classes. distinct can be applied to type classes.

tests/run/utypeclasses.nim

@@ -0,0 +1,13 @@
+import unittest
+
+proc concat(a, b): string =
+  result = $a & $b
+
+test "if proc param types are not supplied, the params are assumed to be generic":
+  check concat(1, "test") == "1test"
+  check concat(1, 20) == "120"
+  check concat("foo", "bar") == "foobar"
+
+test "explicit param types can still be specified":
+  check concat[cstring, cstring]("x", "y") == "xy"
+