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| module type Set = sig | |
| type 'a t | |
| val empty : 'a t | |
| val isEmpty : 'a t -> bool | |
| end | |
| module ListSet : Set = struct | |
| type 'a t = 'a list | |
| let empty = [] | |
| let isEmpty l = l == [] | |
| end | |
| module ListSetExt = struct | |
| include ListSet | |
| (* `len` should not type check if ListSet.t is still abstract *) | |
| let len l = if isEmpty l then 0 else List.length l | |
| let elts = function | |
| | [] -> [] | |
| | h::t -> h::t | |
| end | |
| (* this should not type check as well *) | |
| let _ = ListSetExt.elts (ListSetExt.empty) |
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