Refactor, added forField, subsetOf, and is

Select.js

@@ -1,49 +1,75 @@
 'use strict';
 
+/**
+ * SelectValue - Wraps and pairs an arbitrary value with a reducer.
+ * @class SelectValue
+ * @param {any} value                An arbitrary value to store within.
+ * @param {(Function|null)} resolve  The reducer.
+ */
 class SelectValue {
-	constructor(value, resolve) {
+	constructor(value, resolve = null) {
 		this.value = value;
-		if (resolve) this.resolve = resolve;
+		if (resolve !== null) this.resolve = resolve;
 	}
 }
 
 SelectValue.prototype.resolve = () => null;
 
 class SelectIterable {
-	constructor(values, tests) {
-		this.values = values
-			.map(x => x instanceof SelectValue
-				? x
-				: new SelectValue(x)
-			);
-		this.tests = tests;
+	constructor(values, conditionals) {
+		this.values = values.map(value => value instanceof SelectValue ? value : new SelectValue(value));
+		this.conditionals = conditionals;
 	}
-
-	for(test, consequent) {
-		const self = this;
-		return new SelectIterable(
-			self.values,
-			[ ...self.tests, { test, consequent } ]
-		);
+	for(predicate, consequent) {
+		return new SelectIterable(this.values, [...this.conditionals, { predicate, consequent }]);
+	}
+	forField(...pairs) {
+		var pair;
+		var callback;
+		var even;
+		for (
+			// beforeBegin:
+			var loc = 0;
+			// beforeEvery:
+			even = loc % 2 === 0,
+			// breakPredicate:
+			loc < pairs.length;
+			// afterEvery:
+			loc++
+		) {
+			pair = this.conditionals[this.conditionals.length];
+			if (pair.length === 2) {
+				this.conditionals.push({});
+			};
+			callback = conditionals[loc];
+			if (typeof callback === "object") {
+				if (Array.isArray(callback)) {
+					pair.predicate = callback[0];
+					pair.consequent = callback[0];
+				} else {
+					Object.assign(pair, {
+						predicate: callback.predicate,
+						consequent: callback.consequent
+					});
+				}
+				continue;
+			}
+			if (even) pair.predicate = callback;
+			if (!even) pair.consequent = callback;
+		}
+		return new SelectIterable(this.values, [...this.conditionals, ...conditionals]);
+	}
+	subsetOf(value, consequent) {
+		return this.for(this.value.every(element => element in this.value))
 	}
 }
 
 /* eslint-disable-next-line func-names */
 SelectIterable.prototype.resolve = function (...args) {
-	const self = this;
-	return self.values.map(item => {
-		const resolve = self
-			.tests
-			/* eslint-disable-next-line */
-			.find(x => {
-				return x.test(item.value)
-					? x.consequent
-					: null;
-			});
-		return resolve
-			? resolve.consequent(...args, self.value)
-			: () => null;
-	});
+	return this.values.map(item => {
+		const resolve = this.conditionals.find(tuple => tuple.predicate(item.value) ? tuple.consequent : null);
+		return resolve ? resolve.consequent(...args, this.value) : () => null;
+	}, this);
 };
 
 class Select extends SelectValue {
@@ -51,17 +77,16 @@ class Select extends SelectValue {
 		super(value, resolve);
 		this.iterable = typeof value === "object" && Symbol.iterator in value;
 	}
-
-	for(test, consequent) {
+	for(predicate, consequent) {
 		if (this.iterable) {
-			return new SelectIterable(
-				Array.from(this.value),
-				[ { test, consequent } ],
-			);
+			return new SelectIterable(Array.from(this.value), [{ predicate, consequent }]);
 		}
-		if (test(this.value)) return new Select(this.value, consequent);
+		if (predicate(this.value)) return new Select(this.value, consequent);
 		return this;
 	}
+	is(value, consequent) {
+		return this.for(value === this.value, consequent);
+	}
 }
 
 module.exports = Select;