[Haskell-cafe] Can't get Type 3" to work

Amy de Buitléir amy at nualeargais.ie
Sun Dec 2 19:20:33 UTC 2018


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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