planning

node_modules/@mapbox/mapbox-gl-style-spec/expression/scope.js

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+// @flow
+
+import type {Expression} from './expression.js';
+
+/**
+ * Tracks `let` bindings during expression parsing.
+ * @private
+ */
+class Scope {
+    parent: ?Scope;
+    bindings: {[_: string]: Expression};
+    constructor(parent?: Scope, bindings: Array<[string, Expression]> = []) {
+        this.parent = parent;
+        this.bindings = {};
+        for (const [name, expression] of bindings) {
+            this.bindings[name] = expression;
+        }
+    }
+
+    concat(bindings: Array<[string, Expression]>): Scope {
+        return new Scope(this, bindings);
+    }
+
+    get(name: string): Expression {
+        if (this.bindings[name]) { return this.bindings[name]; }
+        if (this.parent) { return this.parent.get(name); }
+        throw new Error(`${name} not found in scope.`);
+    }
+
+    has(name: string): boolean {
+        if (this.bindings[name]) return true;
+        return this.parent ? this.parent.has(name) : false;
+    }
+}
+
+export default Scope;