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 <amy@nualeargais.ie> 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’

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