Div was introduced in GHC 8.4, I believe. пн, 3 дек. 2018 г. в 05:49, Amy de Buitléir :

Ah, thank you, that makes perfect sense. For anyone else who struggles with that example, you also need :set -XTypeOperators and import GHC.TypeLits.

λ> :set -XDataKinds λ> :set -XTypeOperators λ> import GHC.TypeLits λ> :kind! (1 + 17) * 3 (1 + 17) * 3 :: Nat = 54

Unfortunately, I also get an error on the next line:

λ> :kind! (Div 128 8) ^ 2

<interactive>:1:2: error: Not in scope: type constructor or class ‘Div’

Div is defined in GHC.TypeLits, so I don't understand why that didn't work.

On 2018-12-03 00:12, Brandon Allbery wrote:

That looks like someone had a search-and-replace error.

It used to be that the kind of normal values was *. Type level math made this problematic; by default, in recent ghc that kind is called Type instead. (See the StarIsType LANGUAGE pragma.)

So someone did a search and replace to fix the kinds, and changed what should have been a type level multiplication by accident. Change it to a*.

On Sun, Dec 2, 2018 at 7:09 PM Amy de Buitléir wrote:

...

I'm reading "Thinking with Types" by Sandy Maguire, and there's a bit of code on p. 27 that I don't understand and can't get to work. The "Type 3" seems to have the effect of multiplying by 3.

...

:set -XDataKinds :set -XTypeOperators :kind! (1 + 17) Type 3

(1 + 17) Type 3 :: Nat = 54

But it doesn't work for me. When I try this, I get...

$ ghci --version The Glorious Glasgow Haskell Compilation System, version 8.2.2

$ ghci

λ> :set -XDataKinds λ> :set -XTypeOperators λ> :kind! (1 + 17) Type 3

<interactive>:1:2: error: Not in scope: type constructor or class '+'

<interactive>:1:10: error: Not in scope: type constructor or class 'Type' _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

-- brandon s allbery kf8nh allbery.b@gmail.com

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