[Haskell-cafe] Re: Set Operations In Haskell's Type System

[Bartek Ćwikłowski]

hello,

2010/5/6 John Creighton <johns243a at gmail.com>:

> "a" isa "d" if their exists a "b" and "c" such that the following
> conditions hold:
>
> "a" isa subset of "b",
> "b" isa "c"
> "c" is a subset of "d"

This definition doesn't make sense - it's recursive, but there's no
base case, unless this is some kind of co-recursion.

Are you sure that "subset" isn't what you really want? With subset you
can already ask questions such as "is tabby cat an animal?". If so, my
code (from hpaste) already has this (iirc isDescendentOf ).

regards,
Bartek Ćwikłowski