package.json5

@@ -18,4 +18,7 @@
   devDependencies: {
     mocha: '^11.1.0',
   },
+  dependencies: {
+    'array-keyed-map': '^2.1.3',
+  },
 }

pnpm-lock.yaml

@@ -7,6 +7,10 @@ settings:
 importers:
 
   .:
+    dependencies:
+      array-keyed-map:
+        specifier: ^2.1.3
+        version: 2.1.3
     devDependencies:
       mocha:
         specifier: ^11.1.0
@@ -49,6 +53,9 @@ packages:
   argparse@2.0.1:
     resolution: {integrity: sha512-8+9WqebbFzpX9OR+Wa6O29asIogeRMzcGtAINdpMHHyAg10f05aSFVBbcEqGf/PXw1EjAZ+q2/bEBg3DvurK3Q==}
 
+  array-keyed-map@2.1.3:
+    resolution: {integrity: sha512-JIUwuFakO+jHjxyp4YgSiKXSZeC0U+R1jR94bXWBcVlFRBycqXlb+kH9JHxBGcxnVuSqx5bnn0Qz9xtSeKOjiA==}
+
   balanced-match@1.0.2:
     resolution: {integrity: sha512-3oSeUO0TMV67hN1AmbXsK4yaqU7tjiHlbxRDZOpH0KW9+CeX4bRAaX0Anxt0tx2MrpRpWwQaPwIlISEJhYU5Pw==}
 
@@ -398,6 +405,8 @@ snapshots:
 
   argparse@2.0.1: {}
 
+  array-keyed-map@2.1.3: {}
+
   balanced-match@1.0.2: {}
 
   binary-extensions@2.3.0: {}

src/core/Type.js

@@ -1,3 +1,5 @@
+import {onType} from './helpers.js'
+
 const typeObject = {} // have to make sure there is only one
 
 export const types = () => typeObject
@@ -5,7 +7,8 @@ export const types = () => typeObject
 export class Type {
    constructor(f, options = {}) {
       this.test = f
-      this.from = new Map(options.from ?? [])
+      this.from = options.from ?? onType() // empty Implementations if no ...
+      // ... conversions specified
    }
    toString() {
       return this.name || `[Type ${this.test}]`

src/core/TypeDispatcher.js

@@ -1,11 +1,10 @@
-import {typeOf, Type, bootstrapTypes} from './Type.js'
+import ArrayKeyedMap from 'array-keyed-map'
 
 import {
    Implementations, isPlainFunction, isPlainObject, onType
 } from './helpers.js'
-import {
-   alwaysMatches, matched, needsCollection, Any, Multiple
-} from './TypePatterns.js'
+import {bootstrapTypes, Returns, typeOf, Type} from './Type.js'
+import {matched, needsCollection, Passthru} from './TypePatterns.js'
 
 export class TypeDispatcher {
    constructor(...specs) {
@@ -37,25 +36,39 @@ export class TypeDispatcher {
             continue
          }
          if (typeof val === 'function') {
-            val = onType(Multiple(Any), val)
+            val = onType(Passthru, val)
          }
          if (val instanceof Implementations) {
             if (!(key in this)) {
-               // need to set up the item
+               // Need to "bootstrap" the item:
+               // We initially define it with a temporary getter, only
+               // because we don't know whether ultimately it will produce
+               // a function or a non-callable value, and the "permanent"
+               // getter we want depends on which it turns out to be. This
+               // situation means it's not supported to replace a key
+               // corresponding to a method, after it's been fetched once,
+               // with a definition that produces a non-callable value;
+               // the TypeDispatcher will go on returning a function, and
+               // even if you call that function, it will throw an error
+               // when it tries to call the non-callable value.
+               // Conversely, if you try to replace a key corresponding
+               // to a non-callable value, after it's been fetched once,
+               // with a function, it will work, but it will not be able to
+               // perform type dispatch on that function.
                Object.defineProperty(this, key, {
                   enumerable: true,
                   configurable: true,
                   get: () => {
                      let tryValue
-                     let tryTypes = []
                      try {
                         tryValue = this.resolve(key, [])
                      } catch {
-                        // Has no value for the empty type list, so
-                        // find a type list it will have a value for
-                        tryTypes =
-                           this._implementations[key][0][0].sampleTypes()
-                        tryValue = this.resolve(key, tryTypes)
+                        // Has no value for the empty type list, so therefore
+                        // it must be a method, as there is no way to supply
+                        // any types for a non-function value. Hence, we can
+                        // just make tryValue any plain function, since it is
+                        // never actually used, just its type analyzed.
+                        tryValue = () => undefined
                      }
                      // Redefine the property according to what sort of
                      // entity it is:
@@ -74,7 +87,7 @@ export class TypeDispatcher {
                         })
                         return standard
                      }
-                     if (tryTypes.length) tryValue = undefined
+
                      if (typeof tryValue === 'object') {
                         if (!('resolve' in tryValue)) {
                            tryValue.resolve = types => this.resolve(key, types)
@@ -92,6 +105,7 @@ export class TypeDispatcher {
                         })
                         return get()
                      }
+
                      Object.defineProperty(this, key, {
                         enumerable: true,
                         configurable: true,
@@ -100,13 +114,16 @@ export class TypeDispatcher {
                      return tryValue
                   }
                })
+
+               // Finally, initialize the other data for this key:
                this._implementations[key] = []
-               this._behaviors[key] = new Map()
-               this._dependencies[key] = new Map()
+               this._behaviors[key] = new ArrayKeyedMap()
+               this._dependencies[key] = new ArrayKeyedMap()
             }
+
             // Now add all of the patterns of this implementation:
             for (const [pattern, result] of val.patterns) {
-               if (alwaysMatches(pattern)) {
+               if (pattern === Passthru) {
                   if (key in this._fallbacks) this._disengageFallback(key)
                   this._fallbacks[key] = result
                } else {
@@ -128,7 +145,7 @@ export class TypeDispatcher {
          }
 
          // install value as a catchall value
-         this.merge({[key]: onType(Multiple(Any), val)})
+         this.merge({[key]: onType(Passthru, val)})
       }
    }
 
@@ -151,7 +168,10 @@ export class TypeDispatcher {
          } else {
             const from = state.pos++
             if ('actual' in elt) { // incorporate conversion
-               const convert = elt.matched.from.get(elt.actual)(this)
+               let convert = elt.convertor
+               if (!convert.returns) { // it's a factory that produces convert
+                  convert = convert(this, elt.actual)
+               }
                extractors.push(args => convert(args[from]))
             } else extractors.push(args => args[from])
          }
@@ -167,14 +187,17 @@ export class TypeDispatcher {
       if (this.resolve._genDepsOf?.length) this._addToDeps(key, types)
 
       const behave = this._behaviors[key]
+      // Return the cached resolution if it's there
       if (behave.has(types)) return behave.get(types)
+
+      // Otherwise, perform the resolution and cache the result
       const imps = this._implementations[key]
       let needItem = true
       let item
-      let pattern
       let template
       if (imps.length) {
          for (const options of [{}, {convert: true}]) {
+            let pattern
             for ([pattern, item] of imps) {
                let finalIndex
                ;[finalIndex, template] = pattern.match(types, options)
@@ -189,50 +212,59 @@ export class TypeDispatcher {
       if (needItem && key in this._fallbacks) {
          needItem = false
          item = this._fallbacks[key]
-         template = [types]
+         template = types
       }
       if (needItem) {
          throw new TypeError(`no matching definition of '${key}' on '${types}'`)
       }
-      if (!isPlainFunction(item) || 'returns' in item) {
+      // If this key is producing a non-function value, we're done
+      if (!isPlainFunction(item)) {
          behave.set(types, item)
          return item
       }
-      // item is a Factory. We have to use it to build the behavior
+
+      // item is a function, either a direct behavior or
+      // a factory. We have to use it to build the final behavior
       // First set up to record dependencies
       if (!('_genDepsOf' in this.resolve)) {
          this.resolve._genDepsOf = []
       }
-      this.resolve._genDepsOf.push([key, types])
+
       let theBehavior = () => undefined
+      this.resolve._genDepsOf.push([key, types]) // Important: make sure
+      // not to return without popping _genDepsOf
+      if (!('returns' in item)) {
+         // looks like a factory
          try {
             theBehavior = item(
                DependencyRecorder(this, [], this), matched(template))
          } catch {
             // Oops, didn't work as a factory, so guess we were wrong.
             // Just make it the direct value for this key on these types:
-         behave.set(types, item)
-         return item
-      } finally {
-         this.resolve._genDepsOf.pop()
+            theBehavior = item
          }
-      if (typeof theBehavior === 'function'
-          && theBehavior.length
-          && needsCollection(template)
-      ) {
+      } else theBehavior = item
+
+      let finalBehavior = theBehavior
+      if (typeof theBehavior === 'function') {
+         const returning = theBehavior.returns
+         if (!returning) {
+            throw new TypeError(
+               `No return type specified for ${key} on ${types}`)
+         }
+         if (theBehavior.length && needsCollection(template)) {
             // have to wrap the behavior to collect the actual arguments
-         // in the way corresponding to the template. That may generate
-         // more dependencies:
-         this.resolve._genDepsOf.push([key, types])
-         try {
-            const collectFunction = this._generateCollectFunction(template)
-            theBehavior = (...args) => theBehavior(...collectFunction(args))
-         } finally {
-            this.resolve._genDepsOf.pop()
+            // in the way corresponding to the template. Generating that
+            // argument transformer may generate more dependencies.
+            const morph = this._generateCollectFunction(template)
+            finalBehavior =
+               Returns(returning, (...args) => theBehavior(...morph(args)))
          }
       }
-      behave.set(types, theBehavior)
-      return theBehavior
+
+      this.resolve._genDepsOf.pop()  // OK, now it's safe to return
+      behave.set(types, finalBehavior)
+      return finalBehavior
    }
 
    // Method called to invalidate a set of behaviors

src/core/TypePatterns.js

@@ -20,8 +20,13 @@ class MatchTypePattern extends TypePattern {
       const actual = typeSequence[position]
       if (position < typeSequence.length) {
          if (actual === this.type) return [position + 1, actual]
-         if (options.convert && this.type.from.has(actual)) {
-            return [position + 1, {actual, matched: this.type}]
+         if (options.convert) {
+            for (const [pattern, convertor] of this.type.from.patterns) {
+               const [pos] = pattern.match([actual])
+               if (pos === 1) {
+                  return [position + 1, {actual, convertor, matched: this.type}]
+               }
+            }
          }
       }
       return [-1, Undefined]
@@ -131,8 +136,18 @@ class MultiPattern extends TypePattern {
 }
 
 export const Multiple = item => new MultiPattern(item)
-export const alwaysMatches =
-   pat => pat instanceof MultiPattern && pat.pattern instanceof AnyPattern
+
+// Like Multiple(Any) except leaves the argument list alone; it doesn't
+// chunk it into a single Array of all arguments
+class PassthruPattern extends TypePattern {
+   match(typeSequence, options={}) {
+      const position = options.position ?? 0
+      return [typeSequence.length, typeSequence.slice(position)]
+   }
+   sampleTypes() {return []}
+}
+
+export const Passthru = new PassthruPattern()
 
 // returns the template just of matched types, dropping any actual types
 export const matched = (template) => {

src/core/__test__/TypeDispatcher.spec.js

@@ -1,7 +1,8 @@
 import assert from 'assert'
 import {TypeDispatcher} from '../TypeDispatcher.js'
-import * as numbers from '#number/all.js'
+import * as booleans from '#boolean/all.js'
 import * as generics from '#generic/all.js'
+import * as numbers from '#number/all.js'
 import {onType} from "#core/helpers.js"
 import {Any} from "#core/TypePatterns.js"
 import {Returns} from "#core/Type.js"
@@ -47,4 +48,15 @@ describe('TypeDispatcher', () => {
       gnmath.merge({multiply: plain((a,b) => Math.floor(a) * b)})
       assert.strictEqual(gnmath.square(-2.5), 7.5)
    })
+   it('detects dependencies on conversion operations', () => {
+      const bgn = new TypeDispatcher(booleans, generics, numbers)
+      const {BooleanT, NumberT} = bgn.types
+      assert(!bgn._behaviors.negate.has([BooleanT]))
+      assert.strictEqual(bgn.negate(true), -1)
+      assert(bgn._behaviors.negate.has([BooleanT]))
+      const deps = bgn._dependencies.negate
+      bgn.merge({number: onType([BooleanT], Returns(NumberT, b => b ? 2 : 0))})
+      assert(!bgn._behaviors.negate.has([BooleanT]))
+      assert.strictEqual(bgn.negate(true), -2)
+   })
 })

src/core/__test__/TypePatterns.spec.js

@@ -1,5 +1,7 @@
 import assert from 'assert'
-import {pattern, Any, Multiple, Optional} from '../TypePatterns.js'
+import {
+   pattern, Any, Multiple, Optional, needsCollection
+} from '../TypePatterns.js'
 import {Undefined, TypeOfTypes} from '../Type.js'
 
 describe('Type patterns', () => {
@@ -93,4 +95,10 @@ describe('Type patterns', () => {
          whyNot.sampleTypes(), [Undefined, TypeOfTypes])
       assert(whyNot.equal(whyNot))
    })
+   it('determines whether a template needs a collection function', () => {
+      assert(!needsCollection([Undefined]))
+      assert(needsCollection([Undefined, [Undefined, Undefined]]))
+      assert(needsCollection(
+         [Undefined, {actual: Undefined, matched: TypeOfTypes}]))
+   })
 })

src/core/__test__/helpers.spec.js

@@ -9,8 +9,8 @@ describe('Core helpers', () => {
    it('defines what Implementations are', () => {
       const imps = onType(Undefined, 7, [TypeOfTypes, Undefined], -3)
       assert(imps instanceof Implementations)
-      assert(imps.patterns instanceof Map)
-      assert(imps.patterns.keys().every(k => k instanceof TypePattern))
+      assert(imps.patterns instanceof Array)
+      assert(imps.patterns.every(([k]) => k instanceof TypePattern))
    })
 
    it('detects plain objects', () => {

src/core/helpers.js

@@ -2,12 +2,12 @@ import {pattern} from './TypePatterns.js'
 
 export class Implementations {
    constructor(imps) {
-      this.patterns = new Map()
+      this.patterns = []
       this._add(imps)
    }
    _add(imps) {
       for (let i = 0; i < imps.length; ++i) {
-         this.patterns.set(pattern(imps[i]), imps[++i])
+         this.patterns.push([pattern(imps[i]), imps[++i]])
       }
    }
    also(...imps) {

src/number/NumberT.js

@@ -1,6 +1,7 @@
 import {Type} from '#core/Type.js'
+import {onType} from '#core/helpers.js'
 import {BooleanT} from '#boolean/BooleanT.js'
 
 export const NumberT = new Type(n => typeof n === 'number', {
-    from: [[BooleanT, math => math.number.resolve([BooleanT])]],
+    from: onType(BooleanT, math => math.number.resolve([BooleanT])),
 })

src/number/__test__/NumberT.spec.js

@@ -12,7 +12,14 @@ describe('NumberT Type', () => {
    })
 
    it('can convert from BooleanT to NumberT', () => {
-      const cnvBtoN = NumberT.from.get(BooleanT)(math)
+      const convertImps = NumberT.from
+      let cnvBtoN
+      for (const [pattern, convFactory] of convertImps.patterns) {
+         if (pattern.match([BooleanT])) {
+            cnvBtoN = convFactory(math)
+            break
+         }
+      }
       assert.strictEqual(cnvBtoN(true), 1)
       assert.strictEqual(cnvBtoN(false), 0)
    })