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Author: jhrcek

message-index/messages/GHC-01239/example1/after/IfInFunAppExpr.hs

@@ -3,12 +3,12 @@ module IfInFunAppExpr where
 
 -- Requires BlockArguments language extension to work
 example :: Int
-example = length if True then [1] else
+example = length if True then [1] else []
 
 -- Works without BlockArguments
-example :: Int
-example = length (if True then [1] else [])
+example2 :: Int
+example2 = length (if True then [1] else [])
 
 -- Works without BlockArguments
-example2 :: Int
-example2 = length $ if True then [1] else []
+example3 :: Int
+example3 = length $ if True then [1] else []

message-index/messages/GHC-01239/example1/index.md

@@ -2,7 +2,7 @@
 title: Unexpected if expression in function application
 ---
 
-To pass If-Then-Else expressions as function argument we either have to surround it in parentheses,
+To pass If-Then-Else expressions as function arguments we either have to surround them in parentheses,
 use function application operator `($)` or enable [`BlockArguments`](https://ghc.gitlab.haskell.org/ghc/doc/users_guide/exts/block_arguments.html#extension-BlockArguments) extension.
 
 ## Error Message

message-index/messages/GHC-01239/index.md

@@ -2,7 +2,7 @@
 title: Unexpected if expression in function application
 summary: If expression used as function argument
 severity: error
-introduced: TODO
+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.
@@ -15,5 +15,5 @@ putStrLn (ageMessage 10) -- You are too young to enter
 putStrLn (ageMessage 20) -- Welcome to the club
 ```
 
-Thinking of If-Then-Else expression as a value, we might want to pass it as an input to a function.
-If you do that you can run into the following error.
+Because If-Then-Else expressions return values, it makes sense to pass them as input to a function.
+However, without language extensions, Haskell's grammar requires parentheses around them in function argument positions.