Effective Haskell: Example doesn’t work (page 8)

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Title: Effective Haskell - Example doesn’t work (page 8)

Middle of page 8 says: "Create a new Main.hs and copy the example below to get started.

module Main where

makeGreeting salutation person =
salutation <> " " <> person

Now load up ghci and test out…"

If I load this file into ghci (or try to compile it), I get errors: "The IO action ‘main’ is not defined in the module ‘Main’.

The text shown is not complete as it doesn’t include a main module. The reader is left to figure out why it doesn’t work.

2

Thanks for pointing out that bug! It will be fixed as soon as the next beta update is released.
Until then, the correct example should be:

module Main where

makeGreeting salutation person =
  salutation <> " " <> person

main = print "no salutation to show yet"
3

I am seeing a different error.

Prelude> :load Main
[1 of 1] Compiling Main             ( Main.hs, interpreted )

Main.hs:4:16: error:
    • Variable not in scope: (<>) :: t2 -> [Char] -> t0
    • Perhaps you meant one of these:
        ‘<*>’ (imported from Prelude), ‘*>’ (imported from Prelude),
        ‘>>’ (imported from Prelude)

Main.hs:4:23: error:
    • Variable not in scope: (<>) :: t0 -> t1 -> t
    • Perhaps you meant one of these:
        ‘<*>’ (imported from Prelude), ‘*>’ (imported from Prelude),
        ‘>>’ (imported from Prelude)
Failed, modules loaded: none.

It works if I add import Data.Monoid after the module declaration