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Improve documentation for GHC-01239 #576

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10 changes: 6 additions & 4 deletions message-index/messages/GHC-01239/index.md
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Expand Up @@ -8,11 +8,13 @@ introduced: 9.6.1
Unlike in many other languages, in Haskell the If-Then-Else construct is an expression, which means it returns a value that can be processed further.

```haskell
ageMessage :: Int -> String
ageMessage age = if age < 18 then "You are too young to enter" else "Welcome to the club"
greetUser :: Int -> IO ()
greetUser age = putStrLn (if age < 18
then "You are too young to enter"
else "Welcome to the club")

putStrLn (ageMessage 10) -- You are too young to enter
putStrLn (ageMessage 20) -- Welcome to the club
greetUser 10 -- You are too young to enter
greetUser 20 -- Welcome to the club
```

Because If-Then-Else expressions return values, it makes sense to pass them as input to a function.
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