[the-art] definePropagator -- handles currying

TODO.md

@@ -1,8 +1,7 @@
 # the-art
 
-[the-art] `definePropagator` -- handles currying
 [the-art] `heron.test.ts` -- use currying
-
+[the-art] fix `definePrimitive`
 [the-art] `examples/celsius/`
 
 [the-art] 实现能够处理 interval 的 propagator

src/the-art/propagator/definePrimitive.ts

@@ -1,21 +1,23 @@
 import { repeatApply } from "../../utils/repeatApply.js"
-import {
-  addContent,
-  addPropagator,
-  broadcast,
-  content,
-  createCell,
-  type Cell,
-} from "../cell/index.js"
-import type { Propagator } from "./Propagator.js"
+import { addContent, content, createCell, type Cell } from "../cell/index.js"
 import { type PropagatorDefinitionWithFixedArity } from "./PropagatorDefinition.js"
+import { watch } from "./watch.js"
 
 // 我们知道所有的 primitive 都是函数，
-// 因此如此构建的 propagator，
-// 多个输入和一个输出。
+// 因此所构建的 propagator 有多个输入和一个输出。
 // 注意，这里的 arity 代表 propagator 的参数个数，
 // 而不是函数的输入参数的个数。
 
+// 作为浅嵌入，这里 `definePrimitive` 其实做的是：
+//   "create propagator constructor from native function"
+// 因为真正的 propagator 类似 subscriber，
+// 是可以不带参数就调用的 closure。
+// 但是这个名字太长了，并且为了与深嵌入的 API 一致，
+// 我们用了 define 这个前缀，因为深嵌入的 API 可能是：
+//   definePrimitive(mod, name, arity, fn)
+// 另外 propagator definition 其实是 propagator constructor，
+// 但是叫 definition 也没问题，并且能和深嵌入一致。
+
 export function definePrimitive<A extends number>(
   arity: A,
   fn: (...args: Array<any>) => any,
@@ -66,14 +68,6 @@ export function definePrimitive<A extends number>(
   return definition as unknown as PropagatorDefinitionWithFixedArity<A>
 }
 
-function watch(cells: Array<Cell<unknown>>, propagator: Propagator): void {
-  for (const cell of cells) {
-    addPropagator(cell, propagator)
-  }
-
-  broadcast([propagator])
-}
-
 function liftToCellContents(
   fn: (...args: Array<any>) => any,
 ): (...args: Array<any>) => any {

src/the-art/propagator/definePropagator.ts

@@ -1,15 +1,30 @@
-import type { Cell } from "../cell/index.js"
-import type { PropagatorDefinition } from "./PropagatorDefinition.js"
+import { repeatApply } from "../../utils/repeatApply.js"
+import { createCell, type Cell } from "../cell/index.js"
+import type { PropagatorDefinitionWithFixedArity } from "./PropagatorDefinition.js"
 
-export function definePropagator(
-  arity: number,
+export function definePropagator<A extends number>(
+  arity: A,
   fn: (...args: Array<Cell<unknown>>) => void,
-): PropagatorDefinition {
-  const definiton = (...args: Array<Cell<unknown>>) => {
-    fn(...args)
+): PropagatorDefinitionWithFixedArity<A> {
+  const definition = (...args: Array<Cell<unknown>>) => {
+    if (args.length === arity) {
+      fn(...args)
+    } else if (args.length === arity - 1) {
+      const output = createCell()
+      fn(...args, output)
+      return output
+    } else if (args.length < arity - 1) {
+      const outputs = repeatApply(arity - args.length, () => createCell(), [])
+      fn(...args, ...outputs)
+      return outputs
+    } else {
+      throw new Error(
+        `[definePropagator] number of arguments ${args.length} exceed arity plus one: ${arity + 1}`,
+      )
+    }
   }
 
-  definiton.arity = arity
+  definition.arity = arity
 
-  return definiton
+  return definition as unknown as PropagatorDefinitionWithFixedArity<A>
 }

src/the-art/propagator/watch.ts

@@ -0,0 +1,13 @@
+import { addPropagator, broadcast, type Cell } from "../cell/index.js"
+import type { Propagator } from "./Propagator.js"
+
+export function watch(
+  cells: Array<Cell<unknown>>,
+  propagator: Propagator,
+): void {
+  for (const cell of cells) {
+    addPropagator(cell, propagator)
+  }
+
+  broadcast([propagator])
+}