[Haskell-cafe] Word rigid in "`a' is a rigid type variable..."

Brandon Allbery allbery.b at gmail.com
Wed Nov 13 17:42:31 UTC 2013

On Wed, Nov 13, 2013 at 12:24 PM, Vlatko Basic <vlatko.basic at gmail.com>wrote:

>  Thanks for explanation. If I understood correctly, 'rigid' refers  the
> requirement, not the type itself.

I think that more intuitive/understandable would be something like
>     'b' has too rigid type for 'a' ...

Not really, unless you're talking about some notion of "types of types"
(which exists, but not in this way). You're still trying to hold onto some
notion that `a` is flexible; but the compiler does not care about the kind
of flexibility you want. You will need to let go of that "flexible" for
Haskell's type system to make sense.

(This will make more sense when you start using typeclasses. Or, at least
once you've tried to use your notion of "flexible" with them, because it
will lead you straight into a brick wall that is not flexible at all.)

brandon s allbery kf8nh                               sine nomine associates
allbery.b at gmail.com                                  ballbery at sinenomine.net
unix, openafs, kerberos, infrastructure, xmonad        http://sinenomine.net
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