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Effective Haskell: Chapter 9 - Monad instance error (page 357)

billboswell

billboswell

Effective Haskell: Chapter 9 - Monad instance error (page 357)

Creating the instance of Monad Outlaw described in the text results in error:

• No instance for (Applicative Outlaw)
arising from the superclasses of an instance declaration
• In the instance declaration for ‘Monad Outlaw’

Resolved by adding Applicative instance:

Instance Applicative Outlaw where
pure = return

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First Post!

RebeccaSkinner

RebeccaSkinner

Author of Effective Haskell

Good catch, thanks. I’ll add an errata item about this.

Post #2

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