Type Systems: Sample Polymorphic Type Reconstruction, cont.

Tree7: Tree6, length:?? .? -list?int | length: ?8-list?int [?8 = bool ]

length:?? .? -list?int | (length (cons true null)):int

Tree8: Tree5, Tree7, length:?? .? -list?int | +: int ?int?int

length:?? .? -list?int | (+ (length (cons 1 null)) (length (cons true null))): int

Tree9: Tree3, Tree8

? | (let length := (?x. (if (null? x) then 0 else (+ 1 (length (rest x))))) in (+ (length (cons 1 null)) (length (cons true null)))):int

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