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type -'a obj
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Date: -- (:)
From: Richard Jones <rich@a...>
Subject: type -'a obj
I'm trying to decode this type definition in lablgtk:

type -'a obj

The manual says:

Each type parameter may be prefixed by a variance constraint +
(resp. -) indicating that the parameter is covariant
(resp. contravariant). These type parameters can appear in the type
expressions of the right-hand side of the definition, restricted
eventually by a variance constraint ; i.e. a covariant parameter may
only appear on the right side of a functional arrow (more precisely,
follow the left branch of an even number of arrows), and a convariant
parameter only the left side (left branch of an odd number of arrows).

but this leaves me none the wiser about the +/- before the polymorphic
'a. Can someone explain what this means in plain english?

Thanks,

Rich.

-- 
Richard Jones. http://www.annexia.org/ http://freshmeat.net/users/rwmj
Merjis Ltd. http://www.merjis.com/ - all your business data are belong to you.
"I wish more software used text based configuration files!"
-- A Windows NT user, quoted on Slashdot.