const scopes = [];
    let currentScope = {
      overloads: new Map(),
      parent: undefined,
      typeParameters: undefined
    };

    function createScope(parent, typeParameters = undefined) {
      scopes.push(currentScope);
      currentScope = {
        overloads: new Map(),
        parent,
        typeParameters
      };
    }

    function checkScope() {
      const failures = checkOverloads(
        Array.from(currentScope.overloads.values()),
        currentScope.typeParameters
      );
      addFailures(failures);
      currentScope = scopes.pop();
    }

    function addOverload(signature, key = null) {
      key = key || getOverloadKey(signature);
      if (signature.parent === currentScope.parent && key) {
        const overloads = currentScope.overloads.get(key);
        if (overloads !== undefined) {
          overloads.push(signature);
        } else {
          currentScope.overloads.set(key, [signature]);
        }
      }
    }

    return {
      Program(node) {
        createScope(node);
      },
      TSModuleBlock(node) {
        createScope(node);
      },
      TSInterfaceDeclaration(node) {
        createScope(node.body, node.typeParameters);
      },
      ClassDeclaration(node) {
        createScope(node.body, node.typeParameters);
      },
      TSTypeLiteral(node) {
        createScope(node);
      },
      // collect overloads
      TSDeclareFunction(node) {
        if (node.id && !node.body) {
          addOverload(node, node.id.name);
        }
      },
      TSCallSignatureDeclaration: addOverload,
      TSConstructSignatureDeclaration: addOverload,
      TSMethodSignature: addOverload,
      TSAbstractMethodDefinition(node) {
        if (!node.value.body) {
          addOverload(node);
        }
      },
      MethodDefinition(node) {
        if (!node.value.body) {
          addOverload(node);
        }
      },
      // validate scopes
      'Program:exit': checkScope,
      'TSModuleBlock:exit': checkScope,
      'TSInterfaceDeclaration:exit': checkScope,
      'ClassDeclaration:exit': checkScope,
      'TSTypeLiteral:exit': checkScope
    };