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
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