René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Conditional types - Extract works incorrect ","articleBody":"**TypeScript Version:**  2.8.0-rc, 2.9.0-dev.20180327\r\n\r\n\r\n```ts\r\ndeclare function isFunction\u003cT\u003e(value: T): value is Extract\u003cT, Function\u003e;\r\n\r\ndeclare function toString1(value: object | Function): string ;\r\ndeclare function toString2(value: Function): string ;\r\n\r\nfunction foo\u003cT\u003e(value: T) {\r\n    if (isFunction(value)) {\r\n        toString1(value); // ok\r\n\r\n        toString2(value); // error TS2345: Argument of type 'Extract\u003cT, Function\u003e' is not assignable to parameter of type 'Function'.\r\n                          // Type 'T' is not assignable to type 'Function'.\r\n    }\r\n}\r\n```\r\n\r\n","author":{"url":"https://github.com/sirian","@type":"Person","name":"sirian"},"datePublished":"2018-03-27T10:29:01.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":8},"url":"https://github.com/22899/TypeScript/issues/22899"}