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<p>You can use the (-> c) instance in fun ways<br>
<br>
both :: (a -> b) -> (a, a) -> (b, b)<br>
both = join (***)<br>
<br>
dup :: a -> (a, a)<br>
dup = join (,)<br>
<br>
between `join` (char '"')<br>
<br>
</p>
<div class="moz-cite-prefix">On 10/13/19 11:55 PM, Dannyu NDos
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAKM3oZU93A6XBOYJiUe7iMdbsDL4HCiY6kfQEuyvuvj-rRm1MA@mail.gmail.com">
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<div dir="auto">join is surely useful for Maybe and [].
<div dir="auto"><br>
</div>
<div dir="auto">But IO (IO a)? ReadPrec (ReadPrec a)? ST s (ST s
a)? When the heck could I encounter such types?</div>
</div>
<br>
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