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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Losing generics (composition/currying)","articleBody":"I'm trying to work on [TS typings](https://github.com/donnut/typescript-ramda/) for FP lib [Ramda](http://ramdajs.com/).\r\n[Several](https://github.com/donnut/typescript-ramda/issues/29) [users](https://github.com/donnut/typescript-ramda/issues/78) [have](https://github.com/donnut/typescript-ramda/issues/86) [reported](https://github.com/donnut/typescript-ramda/issues/92) [issues](https://github.com/donnut/typescript-ramda/issues/101) that came down to similar inference issues triggered in the presence of composition/currying involving functions containing generics.\r\nSince FP encourages composing point-free functions (the majority of which use generics for type inference), what breaks here aren't so much edge cases, but idiomatic usage.\r\n\r\n**TypeScript Version:**  nightly (`2.2.0-dev.20161211`)\r\n\r\n**Code** (can paste into the [TS playground](https://www.typescriptlang.org/play/)):\r\n\r\n```ts\r\ndeclare function inc(n: number): number; // +1\r\ndeclare function identity\u003cT\u003e(a: T): T;\r\ndeclare function compose\u003cV0, T1\u003e(fn0: (x0: V0) =\u003e T1): (x0: V0) =\u003e T1;\r\ndeclare function compose\u003cV0, T1, T2\u003e(fn1: (x: T1) =\u003e T2, fn0: (x: V0) =\u003e T1): (x: V0) =\u003e T2;\r\ndeclare function pipe   \u003cV0, T1\u003e(fn0: (x0: V0) =\u003e T1): (x0: V0) =\u003e T1;                           // arity 1: same as compose\r\ndeclare function pipe   \u003cV0, T1, T2\u003e(fn0: (x: V0) =\u003e T1, fn1: (x: T1) =\u003e T2): (x: V0) =\u003e T2;     // arity 2: params swapped\r\n\r\n// don't use generics if it can't resolve them right away:\r\ncompose(identity) // generics lost, now {} =\u003e {}\r\npipe   (identity) // ditto\r\n// argument order apparently matters too:\r\npipe   (inc, identity); // ok, number -\u003e number\r\ncompose(identity, inc); // nope, number =\u003e {}\r\n// also no reasoning backward:\r\ncompose(inc, identity); // {} =\u003e number\r\npipe   (identity, inc); // {} =\u003e number\r\n```\r\n\r\n**Expected behavior:**\r\n- `identity` survives composition\r\n- `identity` not killing the type signature when composing with `inc`\r\n\r\n**Actual behavior:**\r\n- Things break as soon as TS gets a generic it can't immediately resolve (as opposed to keeping them intact).\r\n- Even the same thing using different param order breaks for some reason.\r\n","author":{"url":"https://github.com/KiaraGrouwstra","@type":"Person","name":"KiaraGrouwstra"},"datePublished":"2016-12-11T16:37:43.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/12838/TypeScript/issues/12838"}