update article -- for @spread

README.md

@@ -133,7 +133,7 @@ append @run $result
 
 #### DiffList
 
-[ [Goto The Playground](https://inet.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) ]
+[ [Goto The Playground](https://inet.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) ]
 
 ```inet
 import List from "https://cdn.inet.run/tests/datatype/List.i"
@@ -187,8 +187,17 @@ back zero cons zero cons front @connect value
 back zero cons zero cons front @connect value
 diff_append
 
-// The code above can be simplified
-// by using less named local variables.
+// By using one less local variable `$value`,
+// we can simplify the above code:
+
+(diff) @spread $front $back
+back zero cons zero cons front @connect
+(diff) @spread $front $back
+back zero cons zero cons front @connect
+diff_append
+
+// By using one less local variable `$back`,
+// we can further simplify the above code:
 
 (diff) @spread $front zero cons zero cons front @connect
 (diff) @spread $front zero cons zero cons front @connect

TODO.md

@@ -1,5 +1,3 @@
-update article -- for `@spread`
-
 [note] about spread vs rearrange
 
 `(cons)` -- unconnected node as value -- redesign syntax of rearrange

docs/articles/programming-with-interaction-nets.md

@@ -951,25 +951,13 @@ while the reverse is not true.
 But in interaction nets,
 the relationship between all nodes is symmetric.
 
-In the following code, in one calling of `cons`,
-we will write `(cons :tail)` instead of `cons`,
-this means before calling this node,
-we need to rearrange it's ports,
-view the input port `:tail` as an output port,
-not connect it to the ports in the stack
-but return it directly to the stack.
+In the following code,
+we use `(diff)` to create a new node and return it to the stack,
+follows `@spread` to put all it's ports to the stack
+in reverse order of the definition,
+then we save the ports to local variables for later use.
 
-In the following code, we also used a phrase:
-
-```
-... $value @connect value ...
-```
-
-Which means firstly save the top value in the stack to `$value`,
-then connect the top two ports in the stack,
-finally return the value saved in `$value` back to the stack.
-
-[Goto the playground of `DiffList` and `(diff_append)`](https://inet.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)
+[Goto the playground of `DiffList` and `(diff_append)`](https://inet.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)
 
 ```
 import List from "https://cdn.inet.run/tests/datatype/List.i"
@@ -1010,13 +998,29 @@ end
 import zero from "https://cdn.inet.run/tests/datatype/Nat.i"
 import cons from "https://cdn.inet.run/tests/datatype/List.i"
 
-zero (cons :tail) zero cons diff $value @connect value
-zero (cons :tail) zero cons diff $value @connect value
+(diff) @spread $front $back $value
+back zero cons zero cons front @connect value
+(diff) @spread $front $back $value
+back zero cons zero cons front @connect value
+diff_append
+
+// By using one less local variable `$value`,
+// we can simplify the above code:
+
+(diff) @spread $front $back
+back zero cons zero cons front @connect
+(diff) @spread $front $back
+back zero cons zero cons front @connect
+diff_append
+
+// By using one less local variable `$back`,
+// we can further simplify the above code:
+
+(diff) @spread $front zero cons zero cons front @connect
+(diff) @spread $front zero cons zero cons front @connect
 diff_append
 
-zero (cons :tail) zero cons diff $value @connect value
-zero (cons :tail) zero cons diff $value @connect value
-diff_append @run $result
+@run $result
 ```
 
 # 13

docs/articles/反应网编程.md

@@ -917,24 +917,11 @@ append @run $result
 从树的父节点可以找到子节点，但是反之不行。
 而在反应网中，所有节点之间的关系是对称的。
 
-在下面的代码中，在一次调用 `cons` 时，
-我们写成了 `(cons :tail)` 而不是直接写 `cons`，
-这代表在调用这个节点之前，重新排列这个节点的接口，
-将原本是输入接口的 `:tail` 看成是输出接口一样，
-不是与栈中的接口相连，而是直接返回到栈中。
+在下面的代码中，我们用 `(diff)` 来构造一个新节点返回到栈中，
+后面跟着的 `@spread` 可以将其所有接口按定义中相反的顺序返回到栈中，
+然后我们把这些接口保存到了一些局部变量中。
 
-在下面的代码中我们还使用了一个短语：
-
-```
-... $value @connect value ...
-```
-
-它的意思是，先把栈顶的值保存在 `$value` 中，
-然后将栈顶的两个接口相连，
-最后再把保存在 `$value` 中的值放回栈中。
-
-
-[去 `DiffList` 与 `(diff_append)` 的演算场](https://inet.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)
+[去 `DiffList` 与 `(diff_append)` 的演算场](https://inet.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-eggeWPr-S7peWwkeeUqOS4gOS4quWxgOmDqOWPmOmHjyBgJHZhbHVlYCDvvIzogIznroDljJblpoLkuIvvvJoKCihkaWZmKSBAc3ByZWFkICRmcm9udCAkYmFjawpiYWNrIHplcm8gY29ucyB6ZXJvIGNvbnMgZnJvbnQgQGNvbm5lY3QKKGRpZmYpIEBzcHJlYWQgJGZyb250ICRiYWNrCmJhY2sgemVybyBjb25zIHplcm8gY29ucyBmcm9udCBAY29ubmVjdApkaWZmX2FwcGVuZAoKLy8g5YaN5bCR55So5LiA5Liq5bGA6YOo5Y-Y6YePIGAkYmFja2DvvIzov5vkuIDmraXnroDljJbvvJoKCihkaWZmKSBAc3ByZWFkICRmcm9udCB6ZXJvIGNvbnMgemVybyBjb25zIGZyb250IEBjb25uZWN0CihkaWZmKSBAc3ByZWFkICRmcm9udCB6ZXJvIGNvbnMgemVybyBjb25zIGZyb250IEBjb25uZWN0CmRpZmZfYXBwZW5kCgpAcnVuICRyZXN1bHQ)
 
 ```
 import List from "https://cdn.inet.run/tests/datatype/List.i"
@@ -975,13 +962,27 @@ end
 import zero from "https://cdn.inet.run/tests/datatype/Nat.i"
 import cons from "https://cdn.inet.run/tests/datatype/List.i"
 
-zero (cons :tail) zero cons diff $value @connect value
-zero (cons :tail) zero cons diff $value @connect value
+(diff) @spread $front $back $value
+back zero cons zero cons front @connect value
+(diff) @spread $front $back $value
+back zero cons zero cons front @connect value
+diff_append
+
+// 上面的代码可以少用一个局部变量 `$value` ，而简化如下：
+
+(diff) @spread $front $back
+back zero cons zero cons front @connect
+(diff) @spread $front $back
+back zero cons zero cons front @connect
+diff_append
+
+// 再少用一个局部变量 `$back`，进一步简化：
+
+(diff) @spread $front zero cons zero cons front @connect
+(diff) @spread $front zero cons zero cons front @connect
 diff_append
 
-zero (cons :tail) zero cons diff $value @connect value
-zero (cons :tail) zero cons diff $value @connect value
-diff_append @run $result
+@run $result
 ```
 
 # 13