refactor: avoid inheritance in src/core/TypePatterns

src/core/TypePatterns.js

@@ -5,7 +5,7 @@ const tpBrand = Symbol()
 
 export class TypePattern {
    constructor() {
-      this[tpBrand] = true
+      throw new Error('Cannot construct an abstract TypePattern')
    }
    match(_typeSequence, _options={}) {
       throw new Error('Specific TypePatterns must implement match')
@@ -13,16 +13,15 @@ export class TypePattern {
    sampleTypes() {
       throw new Error('Specific TypePatterns must implement sampleTypes')
    }
-   equal(other) {return other.constructor === this.constructor}
    toString() {return 'Abstract Pattern (?!)'}
 
    // Returns true if entity is a TypePattern
    static holds(entity) {return entity[tpBrand]}
 }
 
-class MatchTypePattern extends TypePattern {
+class MatchTypePattern {
    constructor(typeToMatch) {
-      super()
+      this[tpBrand] = true
       this.type = typeToMatch
    }
    match(typeSequence, options={}) {
@@ -42,13 +41,15 @@ class MatchTypePattern extends TypePattern {
       return [-1, Undefined]
    }
    sampleTypes() {return [this.type]}
-   equal(other) {return super.equal(other) && this.type === other.type}
+   equal(other) {
+      return this.constructor === other.constructor && this.type === other.type
+   }
    toString() {return `Match(${this.type})`}
 }
 
-class SequencePattern extends TypePattern {
+class SequencePattern {
    constructor(itemsToMatch) {
-      super()
+      this[tpBrand] = true
       this.patterns = itemsToMatch.map(pattern)
    }
    match(typeSequence, options={_internal: true}) {
@@ -70,16 +71,16 @@ class SequencePattern extends TypePattern {
       return this.patterns.map(pat => pat.sampleTypes()).flat()
    }
    equal(other) {
-      return super.equal(other)
+      return this.constructor === other.constructor
          && this.patterns.length === other.patterns.length
          && this.patterns.every((elt, ix) => elt.equal(other.patterns[ix]))
    }
    toString() {return `[${this.patterns}]`}
 }
 
-class PredicatePattern extends TypePattern {
+class PredicatePattern {
    constructor(predicate) {
-      super()
+      this[tpBrand] = true
       this.predicate = predicate
    }
    match(typeSequence, options={}) {
@@ -93,7 +94,8 @@ class PredicatePattern extends TypePattern {
       throw new Error('sampleTypes() not yet implemented for PredicatePattern')
    }
    equal(other) {
-      return super.equal(other) && this.predicate === other.predicate
+      return this.constructor === other.constructor
+         && this.predicate === other.predicate
    }
    toString() {return `Test(${this.predicate})`}
 }
@@ -110,7 +112,8 @@ export const pattern = patternOrSpec => {
    throw new TypeError(`Can't interpret '${patternOrSpec}' as a type pattern`)
 }
 
-class AnyPattern extends TypePattern {
+class AnyPattern {
+   constructor () {this[tpBrand] = true}
    match(typeSequence, options={}) {
       const position = options.position ?? 0
       return position < typeSequence.length
@@ -118,14 +121,15 @@ class AnyPattern extends TypePattern {
          : [-1, Undefined]
    }
    sampleTypes() {return [Undefined]}
+   equal(other) {return this.constructor === other.constructor}
    toString() {return 'Any'}
 }
 
 export const Any = new AnyPattern()
 
-class OptionalPattern extends TypePattern {
+class OptionalPattern {
    constructor(item) {
-      super()
+      this[tpBrand] = true
       this.pattern = pattern(item)
    }
    match(typeSequence, options={_internal: true}) {
@@ -143,16 +147,17 @@ class OptionalPattern extends TypePattern {
    }
    sampleTypes() {return []}
    equal(other) {
-      return super.equal(other) && this.pattern.equal(other.pattern)
+      return this.constructor === other.constructor
+         && this.pattern.equal(other.pattern)
    }
    toString() {return `?${this.pattern}`}
 }
 
 export const Optional = item => new OptionalPattern(item)
 
-class MultiPattern extends TypePattern {
+class MultiPattern {
    constructor(item) {
-      super()
+      this[tpBrand] = true
       this.pattern = pattern(item)
    }
    match(typeSequence, options={_internal: true}) {
@@ -170,7 +175,8 @@ class MultiPattern extends TypePattern {
    }
    sampleTypes() {return []}
    equal(other) {
-      return super.equal(other) && this.pattern.equal(other.pattern)
+      return this.constructor === other.constructor
+         && this.pattern.equal(other.pattern)
    }
    toString() {return `${this.pattern}*`}
 }
@@ -179,13 +185,15 @@ export const Multiple = item => new MultiPattern(item)
 
 // 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 {
+class PassthruPattern {
+   constructor () {this[tpBrand] = true}
    match(typeSequence, options={}) {
       const position = options.position ?? 0
       return [typeSequence.length, typeSequence.slice(position)]
    }
    sampleTypes() {return []}
    toString() {return 'Passthru'}
+   equal(other) {return this.constructor === other.constructor}
 }
 
 export const Passthru = new PassthruPattern()