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| // original | |
| const Y = f => (x => f(v => x(x)(v)))(x => f(v => x(x)(v))) | |
| // expanded as | |
| const Y = f => { | |
| // return the result of this IIFE | |
| // f produces the fixed point function | |
| return (x => { | |
| // outer: | |
| f(v => { | |
| // invoke inner x with x as arg, | |
| // returns fixed point which takes v | |
| // f is invoked only once on this side | |
| return x(x)(v) | |
| }) | |
| })(x => { | |
| // inner: | |
| f(v => { | |
| // invoke inner x with x as arg, | |
| // returns fixed point which takes v | |
| // this f is invoked every subsequent time | |
| return x(x)(v) | |
| }) | |
| }) | |
| } |
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Refer to The Mysterious Y-combinator