refactor: change Dispatcher class to a closure

Also starts work on typing that closure. Gets the property names right,
  but currently has the "unfilled" method types, rather than the returned
  "filled-in" function types. Not sure how to fix this.

src/core/Dispatcher.ts

@@ -6,6 +6,7 @@
  */
 
 import {parseReflectedType, ImplementationDef} from './parseReflectedType.js'
+import type {ValueIntersectionByKeyUnion} from '../interfaces/type.js'
 
 // First helper types and functions for the Dispatcher
 
@@ -35,50 +36,103 @@ type TypeSpecification = {
    infer?: (d: DependenciesType) => (z: unknown) => TypeName
 }
 
-type SpecObject = Record<string, Function | TypeSpecification>
+type Callable = (...args: any) => any
+type SpecObject = Record<string, Callable | TypeSpecification>
 type SpecificationsGroup = Record<string, SpecObject>
 
-export class Dispatcher {
-   installSpecification(
-      name: string,
-      defn: ImplementationDef,
-      behavior: Function // possible todo: constrain this type based
-      // on the signature, return type, and dependencies. Not sure if
-      // that's really possible, though.
-   ) {
-      console.log('Pretending to install', name, 'with signatures')
-      for (const signature of defn.fn.signatures) {
-         console.log('   ', signature.args, '=>', signature.returns)
-      }
-      if (defn.fn.aliasOf) {
-         console.log('   As an alias of', defn.fn.aliasOf)
-      }
-      //TODO: implement me
-   }
-   installType(name: TypeName, typespec: TypeSpecification) {
-      console.log('Pretending to install type', name, typespec)
-      //TODO: implement me
-   }
-   constructor(collection: SpecificationsGroup) {
-      const implementations = []
-      for (const key in collection) {
-         console.log('Working on', key)
-         for (const identifier in collection[key]) {
-            const item = collection[key][identifier]
-            if (typeof item === 'function') {
-               implementations.push([key, identifier, item])
-            } else {
-               console.log('Handling type', key, ':', identifier)
-               this.installType(
-                  item.name, collection[key][identifier] as TypeSpecification)
-            }
+// Find all of the keys of an object that are functions but not aliases
+// to another operation
+type BaseOperations<Obj extends SpecObject> =
+   {[K in keyof Obj]:
+    Obj[K] extends Callable
+       ? ReturnType<Obj[K]>['aliasOf'] extends (string | undefined)
+          ? never
+          : K extends string ? K : never
+       : never
+   }[keyof Obj]
+// Gather all of the operations specified in a SpecificationsGroup
+type DispatcherOperations<G extends SpecificationsGroup> =
+   {[K in keyof G]: BaseOperations<G[K]>}[keyof G]
+// Get the type of a given operation in a SpecObject:
+type BaseOperationSignature<
+   Obj extends SpecObject,
+   Name extends BaseOperations<Obj>
+> = ValueIntersectionByKeyUnion<
+   {[K in keyof Obj]:
+    K extends Name
+       ? Obj[K]
+       : Obj[K] extends Callable
+          ? ReturnType<Obj[K]>['aliasOf'] extends (Name | undefined)
+             ? Obj[K] : unknown
+          : unknown
+   },
+   keyof Obj>
+// Get the type of a given operation in a SpecificationsGroup
+type OperationSignature<
+   G extends SpecificationsGroup,
+   Name extends DispatcherOperations<G>
+> = ValueIntersectionByKeyUnion<
+   {[K in keyof G]:
+    Name extends BaseOperations<G[K]>
+       ? BaseOperationSignature<G[K], Name>
+       : unknown},
+   keyof G>
+// Put it all together into the typing of the dispatcher
+type DispatcherInterface<G extends SpecificationsGroup> =
+   {[Op in DispatcherOperations<G>]: OperationSignature<G, Op>}
+
+export function createDispatcher<G extends SpecificationsGroup>(
+   collection: G): DispatcherInterface<G>
+{
+   const implementations = []
+   const types = {} // who knows what the type of this will be
+   const behaviors = {} // ditto
+   for (const key in collection) {
+      console.log('Working on', key)
+      for (const identifier in collection[key]) {
+         const item = collection[key][identifier]
+         if (typeof item === 'function') {
+            implementations.push([key, identifier, item])
+         } else {
+            console.log('Handling type', key, ':', identifier)
+            installType( // In this design, installType would modify
+               // types by side effect; maybe Jos prefers some other
+               // factoring of this?
+               types, item.name,
+               collection[key][identifier] as TypeSpecification)
          }
       }
-      for (const trio of implementations) {
-         const [k, id, imp] = trio
-         console.log('Handling implementation', id, 'from', k)
-         this.installSpecification(
-            id, parseReflectedType(id, imp.reflectedType), imp)
-      }
    }
+   for (const trio of implementations) {
+      const [k, id, imp] = trio
+      console.log('Handling implementation', id, 'from', k)
+      installSpecification(
+         behaviors, id, parseReflectedType(id, imp.reflectedType), imp)
+   }
+   return {} as DispatcherInterface<G>
+}
+
+function installType(
+   types: Object, name: TypeName, typespec: TypeSpecification)
+{
+   console.log('Pretending to install type', name, typespec)
+   //TODO: implement me
+}
+
+function installSpecification(
+   behaviors: Object, // Same issue as mentioned above with side effects...
+   name: string,
+   defn: ImplementationDef,
+   specification: Function // possible todo: constrain this type based
+   // on the signature, return type, and dependencies. Not sure if
+   // that's really possible, though.
+) {
+   console.log('Pretending to install', name, 'with signatures')
+   for (const signature of defn.fn.signatures) {
+      console.log('   ', signature.args, '=>', signature.returns)
+   }
+   if (defn.fn.aliasOf) {
+      console.log('   As an alias of', defn.fn.aliasOf)
+   }
+   //TODO: implement me
 }

src/index.ts

@@ -1,8 +1,12 @@
 import {inspect} from 'node:util'
-import {Dispatcher} from './core/Dispatcher.js'
+import {createDispatcher} from './core/Dispatcher.js'
 import * as Specifications from './all.js'
 
-export default new Dispatcher(Specifications)
+export Specifications
+const math = createDispatcher(Specifications)
+export default math
+
+console.log('Made', math.add}
 
 import {Complex} from './Complex/type.js'
 import {absquare as absquare_complex} from './Complex/arithmetic.js'

src/interfaces/type.ts

@@ -15,7 +15,7 @@ import {$$typeToString} from 'ts-macros'
  * but that's OK, the generic parameter doesn't hurt in those cases.
  ****/
 
-type ValueIntersectionByKeyUnion<T,  TKey extends keyof T> = {
+export type ValueIntersectionByKeyUnion<T,  TKey extends keyof T> = {
   [P in TKey]: (k: T[P])=>void
 } [TKey] extends ((k: infer I)=>void) ? I : never
 

tsconfig.json

@@ -4,6 +4,7 @@
         "rootDir": "./src",
         "outDir": "./build",
         "moduleResolution": "nodenext",
+        "declaration": true,
         "plugins": [ {
             "transform": "ts-macros/dist/type-resolve",
             "transformProgram": true