尝试构造 divergence 的 dup

Author: xieyuheng

docs/std/datatype/Pair.i

@@ -0,0 +1,41 @@
+type Trivial
+
+node sole(-- value!: Trivial)
+node trivialDrop(value!: Trivial --)
+
+rule trivialDrop(value!) sole(value!) {}
+
+type Pair
+
+node pair(
+  left: 'L,
+  right: 'R,
+  ------
+  handle: Trivial,
+  value!: Pair,
+)
+
+node pairDup(
+  target!: Pair,
+  ----------
+  first: Pair,
+  second: Pair,
+)
+
+rule pairDup(target!, first, second) pair(left, right, handle, value!) {
+  let leftFirst, leftSecond = pairDup(left)
+  let rightFirst, rightSecond = pairDup(right)
+  @connect(pair(leftFirst, rightFirst, trivialDrop()), first)
+  @connect(pair(leftSecond, rightSecond, trivialDrop()), second)
+  sole(handle)
+}
+
+function divergence(): Trivial {
+  let left, right, handle, value = pair()
+  let first, second = pairDup(value)
+  @connect(first, left)
+  @connect(second, right)
+  return handle
+}
+
+eval @inspect(divergence())