[refactoring] extract nothing/

src/belief-system/beliefSystemMerge.ts

@@ -1,6 +1,6 @@
 import { Belief } from "../belief/index.js"
-import { isNothing, nothing, type Nothing } from "../cell/index.js"
 import { implies, merge, type MergeConflict } from "../merge/index.js"
+import { isNothing, nothing, type Nothing } from "../nothing/index.js"
 import type { Reasons } from "../reason/index.js"
 import { setIsSubsetOf } from "../utils/set/index.js"
 import { BeliefSystem } from "./BeliefSystem.js"

src/cell/Cell.ts

@@ -1,5 +1,5 @@
+import { nothing, type Nothing } from "../nothing/index.js"
 import type { Propagator } from "../propagator/index.js"
-import { nothing, type Nothing } from "./Nothing.js"
 
 export type Cell<T> = {
   "@type": "Cell"

src/cell/index.ts

@@ -1,4 +1,3 @@
 export * from "./addPropagator.js"
 export * from "./Cell.js"
-export * from "./Nothing.js"
 export * from "./put.js"

src/merge/merge-nothing.ts

@@ -1,5 +1,5 @@
-import { isNothing } from "../cell/index.js"
 import { defineHandler } from "../generic/index.js"
+import { isNothing } from "../nothing/index.js"
 import { merge } from "./merge.js"
 
 function isAnything(x: any): true {

src/merge/merge.ts

@@ -4,26 +4,29 @@ import { defineGeneric } from "../generic/index.js"
 //
 // The contract of the generic function merge is that it takes two
 // arguments the currently known information and the new information
-// being supplied, and returns the new aggregate information.  If the
-// information being supplied is redundant, the merge function should
-// return exactly (by `===`) the original information, so that the
-// cell can know that the news was redundant and not alert its
-// neighbors.  If the new information contradicts the old information,
-// merge should return a distinguished value indicating the
-// contradiction, so that the cell can signal an error. For symmetry
-// and future use, if the new information strictly supersedes the old
-// (i.e., if the old information would be redundant given the new, but
-// the new is not redundant given the old) merge is expected to return
-// exactly (by `===`) the new information.
-
-// # `merge` is not entirely symmetric
+// being supplied, and returns the new aggregate information.
+//
+// - If the information being supplied is redundant, the merge
+//   function should return exactly (by `===`) the original
+//   information, so that (when calling the `put` function) the cell
+//   can know that the news was redundant and not alert its neighbors.
+//
+// - If the new information contradicts the old information, merge
+//   should return a distinguished value indicating the contradiction,
+//   so that the cell can signal an error. For symmetry and future
+//   use.
+//
+// - If the new information strictly supersedes the old (i.e., if the
+//   old information would be redundant given the new, but the new is
+//   not redundant given the old) merge is expected to return exactly
+//   (by `===`) the new information.
 //
-// If the first and second arguments represent equivalent information
-// but are not equal (by `===`), merge must return the first rather
-// than the second. This is a consequence of the asymmetry in the
-// cells’ treatment of their existing content versus incoming
-// content. Having merge return the wrong one could lead to spurious
-// infinite loops.
+// - If the first and second arguments represent equivalent
+//   information but are not equal (by `===`), merge must return the
+//   first rather than the second. This is a consequence of the
+//   asymmetry in the cells’ treatment of their existing content
+//   versus incoming content. Having merge return the wrong one could
+//   lead to spurious infinite loops.
 
 export const merge = defineGeneric()
 

src/monad/belief-monad.ts

@@ -1,6 +1,6 @@
 import { Belief, isBelief } from "../belief/index.js"
-import { isNothing, nothing } from "../cell/Nothing.js"
 import { defineHandler } from "../generic/index.js"
+import { isNothing, nothing } from "../nothing/index.js"
 import { isFunction } from "../utils/isFunction.js"
 import { setUnion } from "../utils/set/index.js"
 import { bind, flatten, fmap } from "./monad.js"

src/monad/nothing-monad.ts

@@ -1,5 +1,5 @@
-import { isNothing, nothing } from "../cell/Nothing.js"
 import { defineHandler } from "../generic/index.js"
+import { isNothing, nothing } from "../nothing/index.js"
 import { isFunction } from "../utils/isFunction.js"
 import { flatten, fmap } from "./monad.js"
 

src/nothing/index.ts

@@ -0,0 +1 @@
+export * from "./Nothing.js"